JP2010158631A - Diffusion plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffusion plate capable of maintaining the initial performance even in severe use conditions likely to cause the clogging of an aerobic biological reaction tank or the like of sewage and industrial wastewater. <P>SOLUTION: The diffusion plate 1 comprises a thin plate which has a first surface in contact with liquid and a second surface in contact with air, and is provided with a plurality of aeration holes 5, and disperses air bubbles into the liquid through the aeration holes. An opening of each aeration hole has a first width in the first surface, and has a second width in the second surface, which is smaller than the first width. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a diffuser plate.

  A diffuser plate is used in transferring oxygen from a gas phase to a liquid phase by gas-liquid contact, particularly in transferring oxygen to a water treatment tank using an aerobic biological reaction. Various diffusers and diffusers have been proposed to increase the efficiency of oxygen transfer.

  For example, an air diffuser that foams from a metal plate having fine slit-like holes has been proposed (see, for example, Patent Document 1). In this, since the pressure loss is small and fine bubbles can be generated, high oxygen transfer efficiency can be obtained.

However, when the diffuser plate is used by being immersed in an aerobic biological reaction tank for sewage or factory wastewater, the microorganisms contained in the water to be treated enter and adhere to the inside of the hole, thereby clogging the hole. Occurs. As a result, there are problems such as uneven foaming and reduced oxygen transfer efficiency, and increased pressure loss, making it impossible to supply the necessary amount of air to the diffuser plate.
JP 2006-61817 A

  The present invention solves the above-mentioned problems, and a diffuser plate capable of maintaining the initial performance even under severe use conditions such as sewage and aerobic biological reaction tanks for industrial wastewater that are likely to be clogged. The purpose is to provide.

The air diffuser plate according to the present invention comprises a thin plate having a first surface in contact with a liquid and a second surface in contact with air, and provided with a plurality of air diffuser holes. Air bubbles are introduced into the liquid through the air diffuser holes. A diffuser plate to disperse,
The opening of the air diffusion hole has a first width on the first surface and a second width on the second surface, and the second width is smaller than the first width. Features.

  ADVANTAGE OF THE INVENTION According to this invention, the diffuser board which can maintain an initial stage performance also in the severe use conditions which a clogging of aerobic biological reaction tanks, such as a sewage and a factory wastewater, tends to produce is provided.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a plan view of a diffuser plate according to an embodiment of the present invention. As shown in the figure, the diffuser plate 1 is composed of a thin plate having a plurality of diffuser holes (slits) 5. The material of the thin plate is usually stainless steel, titanium, aluminum, copper, silver or an alloy containing them as a main component. In particular, when stainless steel or titanium is used, it is easy to form a uniform oxide film on the surface and to obtain a uniform foamed state. When silver is contained, the effect of suppressing the growth of microorganisms in the thin plate is high, and the effect can be maintained for a long time. The shape of the diffuser plate 1 is not particularly limited and can be arbitrarily determined. What is necessary is just to determine suitably the shape and dimension of the diffuser hole 5, and the pitch arrange | positioned.

  When applied to water to be treated containing a large amount of microorganisms, such as an aerobic biological reaction tank for treating sewage and industrial wastewater, microorganisms enter and adhere to the inside of the diffuser holes 5 of the diffuser plate 1. Clogging is likely to occur. In the present invention, the opening width of the air diffusion hole is set to a different value between the surface in contact with the liquid and the surface in contact with the air. Specifically, the problem of adhesion of microorganisms can be avoided by making the opening width on the surface in contact with air smaller than the opening width on the surface in contact with the liquid. The opening width of the diffuser holes refers to the maximum width and the maximum length of the opening when the opening shape on each surface has a longitudinal direction. Moreover, when the opening shape in each surface is circular, it refers to the diameter of the opening.

  Here, the cross-sectional shape of the air diffusion hole 5 in the air diffusion hole 1 in the air diffusion plate shown in FIG. 1 is shown in FIG. The cross section shown in the figure can be, for example, a cross section in the longitudinal direction of an opening-shaped diffused hole having a longitudinal direction.

  As shown in FIGS. 2A to 2D, the opening of the air diffusion hole 5 has different widths on the first surface 1a in contact with the liquid and the second surface 1b in contact with the air. Specifically, the second opening width in the second surface 1b is smaller than the first opening width in the first surface 1a. As shown in FIG. 2A, the cross section of the air diffusion hole 5 does not necessarily need to be a tapered shape having a symmetrically continuous slope.

  It may be a left-right asymmetric shape as shown in FIG. 2B or a curved shape as shown in FIG. Depending on the case, it may be changed stepwise as shown in FIG.

  The diffused holes can be processed by, for example, a punching method, an etching method, a drilling method, or the like, and the processing method is selected according to the cross-sectional shape of the diffused holes. The tapered shape shown in FIGS. 2A and 2B can be formed by a punching method, and the tapered shape shown in FIG. 2C can be formed by an etching method. Further, the tapered shape shown in FIG. 2 (d) is a shape that can be easily processed by a drilling method.

  Since the opening width of the diffuser holes on the lower surface side (second surface) in contact with air is smaller than the opening width on the upper surface side (first surface) in contact with the liquid, the diffuser plate according to the embodiment of the present invention is sewage It has become possible to suppress the intrusion of water. Such knowledge has been found by the present inventors.

In the case of a shape having a length, the opening shape of the air diffusion holes 5 on the first surface 1a is not particularly limited. As shown in FIG. 3, the opening shape of the air diffusion holes 5 can be various shapes. Specific examples include a quadrangle, an ellipse, a crescent shape, and a trapezoid. The second surface 1b may have an opening shape similar to that of the first surface 1a. The maximum width and the maximum length of the opening shape of the diffuser hole 5 having such a length can be expressed by using W _max and L _max , respectively, as shown in FIG.

Here, the maximum width and maximum length of the diffuser holes 5 on the first surface 1a are W1 _max and L1 _max , respectively, and the maximum width and maximum length of the diffuser holes 5 on the second surface 1b are W2 _max and L2 respectively. _Let it be _max . In each of the first surface 1a and the second surface 1b, the maximum length (W _max ) is larger than the maximum width (L _max ).

In the diffuser plate according to the embodiment of the present invention, the second maximum width W2 _max on the lower surface side is defined to be smaller than the first maximum width W1 _max on the upper surface side. In particular, the second maximum width W2 _max is the case of 0.8 times or less of W1 _max of the first maximum width, is advantageous in that entry into sewage diffusing pores inside is difficult. When the second maximum width W2 _max is excessively reduced with respect to the first maximum width W1 _max , the effect is not significantly enhanced. Rather, since the opening resistance on the lower surface side with respect to air is significantly reduced, there is a possibility that the ventilation resistance may increase drastically. Therefore, the second maximum width W2 _max is 0.5 times or more of the first maximum width W1 _max. Is desired.

Although the generated bubbles tend to be finer as the first maximum width W1 _max is smaller, if it is too small, the pressure loss of the diffuser plate becomes very large, which is disadvantageous in terms of energy. On the other hand, if the first maximum width W1 _max is too large, air bubbles generated becomes coarse, oxygen transfer efficiency as a result may be lowered. In order to secure a sufficiently large oxygen transfer efficiency while keeping the pressure loss within an allowable range, it is desirable that the first maximum width W1 _max is in the range of 0.02 mm to 0.3 mm.

Similarly to the first maximum width W1 _max described above, the first maximum length L1 _max is disadvantageous in terms of energy when it is too small, and there is a possibility that the oxygen transfer efficiency is lowered when it is too large. Considering these, it is preferable to define the first maximum length L1 _max within a range of 0.1 mm to 2 mm.

  The opening shape of the air diffusion holes in the first surface 1a and the second surface 1b may be circular. As in the case of the shape having the longitudinal direction, the second diameter R2 of the second surface 1b on the lower surface side is defined to be smaller than the first diameter R1 of the first surface 1a on the upper surface side. In particular, when the second diameter R2 is 0.8 times or less than the first diameter R1, it is advantageous in that it is difficult to enter the sewage into the air diffusion holes. When the second diameter R2 is made excessively smaller than the first diameter R1, the effect is not significantly enhanced. Rather, since the opening resistance on the lower surface side in contact with the air may be significantly reduced, the ventilation resistance may be drastically increased. Therefore, the second diameter R2 may be 0.5 times or more the first diameter R1. desired.

  Although the generated bubbles tend to be finer as the first diameter R1 on the first surface is smaller, if it is too small, the pressure loss of the diffuser plate becomes very large, which is disadvantageous in terms of energy. On the other hand, when the first diameter R1 is too large, the generated bubbles become coarse, and as a result, the oxygen transfer efficiency may be reduced. In order to secure a sufficiently large oxygen transfer efficiency while keeping the pressure loss within an allowable range, it is desirable that the first diameter R1 be in the range of 0.02 mm to 0.3 mm.

  FIG. 5 shows a cross-sectional view of an example of the air diffuser using the air diffuser plate 1 as described above. In the diffuser 10 shown in the figure, the diffuser plate 1 is mounted on the upper part of the casing 4 by the diffuser plate fixing frame 2, and the casing 4 communicates with the air supply pipe 3. A check valve 11 is provided between the casing 4 and the air supply pipe 3. In FIG. 5, reference numeral 13 indicates a gap between the diffuser plate 1 and the casing 4.

  Since the air diffuser plate 1 is provided with the air diffuser holes having a specific shape, the intrusion of sewage is suppressed, and problems due to clogging can be avoided. That is, since uniform foaming is maintained, the oxygen transfer efficiency does not decrease, and the pressure loss does not increase and the amount of air necessary for air diffusion does not become difficult. Therefore, the diffuser using the diffuser plate of the present invention can be operated continuously over a long period of time.

A SUS316L plate having a thickness of 0.3 mm was prepared, and a diffuser plate was prepared by providing a diffuser hole. The shapes and dimensions of the openings of the provided air diffusion holes are summarized in Tables 1 and 2 below.

  In the table, the correspondence with the plot in FIG. 6 described later is also shown.

  Since the opening width in the first surface is larger than the opening width in the second surface, the diffuser plates of Examples 1 and 2 both have a tapered shape. The diffuser plates of Comparative Examples 1 and 2 have the same opening widths on the first surface and the second surface, and have no taper.

Each diffuser plate was installed in the activated sludge treatment reaction tank, and the actual drainage was diffused. The installed water depth of the diffuser plate was 1 m, the diffused amount per diffuser plate area was 35 Nm ³ / hr / m ² , and the pressure loss was examined. The pressure loss of the diffuser plate was determined by the following method. Specifically, a pressure sensor was installed in the casing holding the diffuser plate, and the total pressure loss in the casing was measured. The pressure loss of the diffuser plate was determined by subtracting the pressure loss of 1000 mm-aq for the water depth from this measured value.

  The operating status of the activated sludge treatment reactor during data measurement is as follows. In addition, a numerical value is an average value.

Processing time (residence time): 24 hr
Solid matter concentration (MLSS concentration): 3050 mg / L
The graph of FIG. 6 shows the change over time of the pressure loss for the diffuser plates of Examples 1 and 2 and Comparative Examples 1 and 2.

  When the opening shape is rectangular, that is, when Example 1 and Comparative Example 1 are compared, the initial pressure loss at the start of continuous aeration is comparable. When there is no taper (Comparative Example 1), it is 92 mm-aq, and when there is a taper (Example 1), it is 94 mm-aq.

  The pressure loss of the diffuser plate of Comparative Example 1 was confirmed to increase immediately after the start of the aeration. It reaches 400 mm-aq after about 20 days, and reaches 560 mm-aq after 80 days. When the pressure loss exceeds 600 mm-aq, it is difficult to continue the continuous aeration unless a recovery operation such as chemical cleaning is performed.

  On the other hand, although the pressure loss of the diffuser plate of Example 1 showed a gradual increase immediately after the start of the aeration, it has stabilized after about 20 days and has changed between 200 and 300 mm-aq. If the pressure loss is about 400 mm-aq or less, the pressure loss is not substantially affected, and thus is within an allowable range. Therefore, the diffuser plate of Example 1 was capable of continuous aeration operation even after 80 days.

  When the opening shape is circular, that is, when Example 2 and Comparative Example 2 are compared, the initial pressure loss at the start of continuous aeration is substantially the same. When there is no taper (Comparative Example 2), it is 259 mm-aq, and when there is a taper (Example 2), it is 260 mm-aq.

  The pressure loss of the diffuser plate of Comparative Example 2 rapidly increased immediately after the start of the aeration, and reached 600 mm-aq after about 41 days. For this reason, it was difficult for the air diffusing plate of Comparative Example 2 to continue the continuous air diffusing unless a recovery operation such as chemical cleaning was performed.

  On the other hand, although the pressure loss of the diffuser plate of Example 2 showed a moderate increase immediately after the start of the aeration, it has stably changed between 300 and 400 mm-aq after about 30 to 40 days. . As described above, if the pressure loss is about 400 mm-aq or less, the pressure loss is not substantially affected, and thus is within an allowable range. Therefore, the diffuser plate of Example 2 was capable of continuous aeration operation even after 40 days had elapsed.

  From the above results, it was confirmed that the diffuser plate of the example has a small change in pressure loss with time and can maintain the initial performance even under severe use conditions.

  In addition, regarding the opening shape, the bubble diameter is affected by the contact length with the air diffuser, and if this is small, the bubble diameter is also small. When the hole is circular, the bubble contacts the entire circumference of the hole, grows and desorbs, and the entire circumference of the hole becomes the contact length. On the other hand, when the hole is rectangular, the bubble grows and desorbs by contacting only part of two long sides among the four sides forming the hole. When the peripheral lengths of the holes are about the same, bubbles having a smaller diameter can be generated in the rectangular shape. Therefore, like a circular hole, since the diameter of the bubble can be reduced without increasing the pressure loss and the oxygen dissolution efficiency can be increased without increasing the pressure loss, the rectangular hole is preferable.

The enlarged view of the surface of the diffuser plate concerning one Example of this invention. The figure which shows an example of the cross-sectional shape of an air diffusion hole. The figure which shows an example of the planar shape of an air diffusion hole. The figure which shows an example of the planar shape of an air diffusion hole. Sectional drawing which shows an example of an air diffuser. The graph which shows the daily change of a diffuser plate pressure loss.

DESCRIPTION OF SYMBOLS 1 ... Air diffuser plate; 1a ... 1st (liquid side) surface; 1b ... 2nd (air side) surface 2 ... Air diffuser plate fixed frame; 3 ... Air supply pipe; 4 ... Casing; 5 ... Air diffuser hole 10 ... Air diffuser; 11 ... Check valve; 13 ... Gap.

Claims (5)

A diffuser plate having a first surface in contact with a liquid and a second surface in contact with air, comprising a thin plate provided with a plurality of air diffusion holes, and disperses bubbles in the liquid through the air diffusion holes;
The opening of the air diffusion hole has a first width on the first surface and a second width on the second surface, and the second width is smaller than the first width. A diffuser plate featuring. The opening shape of the air diffusion hole is a shape having a length having a first maximum width W1 _max and a first maximum length L1 _max on the first surface, and a second maximum width on the second surface. W2 _max and the second maximum length L2 _max have a longitudinal shape, and are characterized by W1 _max ≦ L1 _max, W2 _max ≦ L2 _max , 0.5W1 _max ≦ W2 _max ≦ 0.8 W1 _max The diffuser plate according to claim 1. The first maximum width W1 _max of the air diffuser is 0.02 to 0.3 mm, and the first maximum length L1 _max is 0.1 to 2 mm. Diffuser.   The opening shape of the air diffuser has a circular shape with a first diameter R1 on the first surface, a circular shape with a second diameter R2 on the second surface, and 0.5R1 ≦ R2 ≦. The diffuser plate according to claim 1, wherein the diffuser plate is 0.8R1.   The diffuser plate according to claim 4, wherein the first diameter R1 of the diffuser hole is 0.02 to 0.3 mm.

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