JP4489638B2 - Air diffuser - Google Patents

Description

  The present invention relates to an air diffuser for supplying oxygen into an aeration tank when an organic sludge such as sewage or industrial wastewater is treated with activated sludge.

  When an organic sludge such as sewage or industrial wastewater is treated with activated sludge, an air diffuser is used to supply oxygen into the aeration tank. In a diffuser, a porous body in which ceramic or plastic fine particles are sintered at a high temperature into a plate shape or a cylindrical shape is widely used.

  In the air diffuser, reducing the power of the aeration blower is an important issue. In particular, it is required to improve the oxygen dissolution efficiency by increasing the contact area of gas and liquid by reducing the generated bubbles under conditions that do not increase pressure loss so much. For this purpose, it is necessary to make the opening of the diffuser surface smaller.

  In a porous sintered body of ceramic or plastic fine particles, in order to reduce the opening of the diffuser surface, sintering is performed using a smaller particle diameter. However, in that case, since the pore diameter of the sintered body is also reduced, the pores are blocked by dust in the aerated air or organic sludge that flows backward when aeration is stopped, and pressure loss increases. Therefore, there is a limit to reducing the pore diameter.

  In addition, since the ceramic sintered body has a low bending strength, the thickness needs to be about 10 to 40 mm in order to prevent cracking due to external force or air pressure. As dust and sludge accumulate in the pores in the ceramic sintered body, the clogging proceeds and the pressure loss gradually increases. Here, since there is an upper limit to the discharge pressure of the blower, in order to reduce the pressure loss, the diffuser element must be washed appropriately. However, since it is heavy, it is difficult to lift it, and maintenance cannot be performed unless the aeration tank is emptied. Furthermore, since the ceramic sintered body is easily cracked, the diffusion area per sheet must be reduced, which increases the number of installations and increases the cost.

  In addition, the problem that the organic waste water flows backward when the aeration is stopped to block the diffuser element is fatal. In general, continuous aeration has to be performed. Therefore, the diffuser using the ceramic sintered body also has a problem in operation management.

  In recent years, in order to solve the above problems, an air diffuser using a rubber membrane has been developed and put into practical use. This is a device that uses a rubber thin film with slits. When aeration occurs, the rubber expands to open the slits and generate bubbles, and when aeration stops, the slits close to prevent backflow of sewage. . In this way, the problem that the diffuser element is blocked is solved by using the rubber membrane. In addition, as a material of rubber, there are those using EMDM rubber and those using stronger urethane rubber.

  However, in the case of a rubber membrane, the shrinkage of the rubber is lowered by long-term use. In that case, the slit opening / closing function becomes insufficient, and the slit is in a half-open state even when aeration is stopped, so dust and sludge may adhere to the opening and increase pressure loss. On the other hand, when the crack progresses in the slit due to the deterioration of the rubber due to aging, the generated bubbles become large and the oxygen dissolution efficiency decreases. Therefore, it is necessary to replace the rubber thin film every five years.

  If the slit is made small in order to reduce the bubble diameter, the air supply pressure for opening the slit must be increased, and even if the oxygen dissolution efficiency is improved and the supply air amount is reduced, the supply pressure is reduced. Since it becomes higher, the aeration power is offset.

  Japanese Patent Laid-Open No. 2001-334288 discloses an air diffuser using a filter cloth. According to the publication, the rubber membrane as described above is expensive and easily deteriorates after long-term use. Instead, it is a relatively inexpensive and strong filter cloth used in a dehydrator. It has been proposed to use Even if the filter cloth is used for a long time, there are few problems of breakage and blockage, and the operating cost of the air diffuser can be reduced.

However, when using a filter cloth, the development of a structure to generate small bubbles, measures to prevent the backflow of sewage, and measures to prevent deterioration associated with the stretching of the filter cloth fibers due to pressure during aeration should be solved. Many challenges remain.
JP 2001-334288 A

  The present invention has been made in view of the problems of the conventional air diffuser as described above, and an object of the present invention is to increase the pressure loss of the air diffuser element so as to ensure the oxygen dissolution efficiency. It is an object of the present invention to provide an air diffuser capable of causing fine bubbles and preventing backflow of sewage during aeration stop, which is the main cause of blockage of the air diffuser element.

The air diffuser of the present invention comprises:
A diffuser using a mesh cloth in which fibers are woven in plain weave, twill weave, oblique weave, or sousse weave,
The mesh cloth is composed of a monofilament yarn made of polyarylate having a wire diameter of 10 to 100 μm, woven with a mesh of 100 to 1000 mesh (number of yarns between inches), and an opening size of 5 to 200 μm. It is characterized by being.

  According to the air diffuser of the present invention, air bubbles having a diameter of about 1 mm can be generated by using a mesh cloth manufactured under the above conditions on the air diffuser surface. Thereby, oxygen dissolution efficiency can be improved. Furthermore, when aeration is stopped, the backflow of sewage can be prevented by the surface tension of the water film formed between the meshes.

Preferably, the mesh cloth includes a first layer disposed on the back side, and a second layer laminated thereon,
The first layer is composed of a cloth having a wire diameter of 10 to 100 μm, woven with 100 to 1000 mesh, and having an opening size of 5 to 200 μm,
The second layer is made of fibers having the same strength per unit cross-sectional area as the fibers of the first layer, and is woven with 10 to 200 mesh using a thread having a wire diameter of 30 to 200 μm, and the opening size is set to 50 to 800 μm. Consists of crosses.

  Here, the first layer is a mesh cloth for generating fine bubbles and preventing backflow. Since this first layer is woven with a relatively thin thread, it is easy to break, and the distance between adjacent openings is small, and bubbles tend to be polymerized into large bubbles. Therefore, by covering the first layer with a second layer woven with a thread having the same strength per unit cross-sectional area and having a relatively large opening size, the bubble size and density are maintained while maintaining the size. Stretching can be prevented. Such a second layer also serves to prevent bubble polymerization.

  In that case, preferably, the first layer and the second layer are integrated by pressure bonding.

Preferably, the mesh cloth is attached to the frame with a tension of 0.1 N / cm or more. In this way, by attaching the mesh cloth to the frame in a state where a tension much larger than the pressure at the time of aeration is applied, elongation of the mesh cloth during aeration can be suppressed. Thereby, the internal force of the fiber is kept almost constant regardless of the presence or absence of aeration, and deterioration due to repeated stress is prevented.
The upper limit of the tension is about 30 N / cm.

  Preferably, the mesh cloth attached to the frame is disposed on the upper surface of the box-shaped holder.

  Preferably, a filter having a dust trapping particle size of 1 to 300 μm is inserted in the holder or in a joint portion of the air supply pipe to the holder. Thus, by inserting the filter, dust in the supply air can be captured to prevent clogging of the mesh cloth, and continuous use for a long time can be ensured.

  According to the aeration apparatus of the present invention, by generating bubbles having a diameter of about 1 mm, it is possible to improve the oxygen dissolution efficiency and reduce the power required for aeration. Furthermore, when aeration is stopped, the backflow of sewage can be prevented by the surface tension of the water film formed between the meshes.

  The present invention has been made with the aim of increasing the oxygen dissolution efficiency by reducing the generated bubbles, not increasing the pressure loss of the diffuser element, preventing the backflow of sewage and enabling intermittent aeration. is there. In order to realize such a state, in the air diffusing device of the present invention, fibers having a wire diameter of 10 to 100 μm are formed on the air diffusing surface in a plain weave or twill weave with 100 to 1000 mesh (number of yarns between inches). Woven mesh cloth is used. This mesh cloth has a fine opening of 5 to 200 μm. The fibers may be monofilaments (single fibers) or multifilaments (multiple fibers). As fibers capable of realizing small openings with high strength and a large number of meshes by weaving, for example, polyarylate monofilaments are available.

  The most suitable for generating small bubbles is 400 mesh, in which case the wire diameter that can be woven is about 30 μm and the opening is about 30 μm. Since such mesh cloth has a small opening, sewage does not flow backward due to surface tension, and thus has a backflow prevention function when aeration is stopped. If the mesh is larger than this, the pressure loss increases and the power of the blower increases, so the overall power efficiency decreases, which is not a good idea.

  However, when such a mesh cloth is used alone for the diffuser element, when the pressure of the aerated air is high, the fibers of the mesh cloth 1 are stretched as shown in FIGS. Therefore, the generation of bubbles may be intermittent in a pulsating state rather than continuous foaming. In addition, since thin fibers are used, the distance between adjacent openings is small, and depending on the conditions used, the generated bubbles 2 are superposed and large bubbles are generated as shown in FIG. There is.

  Therefore, in order to prevent expansion of the mesh cloth 11 (first layer) for air diffusion (which also functions to generate bubbles and prevent sewage backflow) and to prevent polymerization of bubbles, as shown in FIG. Further, a mesh cloth (second layer) having a coarse mesh using fibers having equivalent strength is overlapped to form a multilayer structure of two layers or more. The mesh mesh 12 of the upper layer is woven from 10 to 200 mesh having a wire diameter of 30 to 200 μm. In this case, the opening is 50 to 800 μm. Examples of the fiber material include polyarylate monofilaments having high strength and low elongation.

  In addition, since the mesh cloth having a multilayer structure integrated by pressure bonding is as thin as 1,000 μm or less, dust and sludge are not easily accumulated in the opening of the mesh cloth. Even if the sludge 3 and dust block the opening of the mesh cloth 11 when aeration is stopped, as shown in FIGS. 4A and 4B, flushing is easily performed by aerated air. Therefore, there is no increase in pressure loss due to sludge blockage.

  FIG. 5 shows an example of the air diffusion element 14 configured by attaching the mesh cloths 11 and 12 to the frame 13. In this example, a two-layer mesh cloth is used, and this mesh cloth is attached to the frame under tension so that the fibers are not stretched by the pressure of aerated air. Thus, by applying tension in advance, the extension of the fiber during aeration is suppressed, and the deterioration of the fiber due to repeated expansion and contraction is prevented.

  Further, if necessary, in order to prevent the mesh cloth opening from being blocked by dust contained in the supply air, as shown in FIG. 6, a dust capturing filter 15 is provided upstream of the mesh cloth of the air diffusion element. Can also be installed.

  As shown in FIG. 7A, in the state where there is no filter, dust in the air may adhere to the lower layer 11 of the mesh cloth and cause clogging. As shown in FIG. 7B, by installing the filter 15, dust 5 in the air is captured by the filter 15, so that the mesh cloth can be prevented from being blocked and an increase in pressure loss can be prevented. In addition, Preferably, the filter 15 uses a nonwoven fabric with a large porosity, etc., and makes the dust collection particle diameter about 1-300 micrometers.

  The filter 15 only needs to be replaced during maintenance, and does not require chemical cleaning or the like, which is a problem in the case of a ceramic air diffusion element, and is relatively easy to manage.

  FIG. 8 shows another example of the filter arrangement. In this example, the air diffusion element 14 (mesh cloth 11 and 12 attached to the frame 13) is attached to the upper surface of the box-shaped holder 16. A supply air pipe 17 is connected near the end of the holder 16. The dust capturing filter 18 is accommodated in a pocket provided at a connection portion between the supply air pipe 17 and the holder 16.

Table 1 shows the results of measuring the oxygen dissolution efficiency and pressure loss of an air diffuser using a two-layer type mesh cloth according to the present invention. For comparison, this table also shows the test results for a diffuser using a conventional sintered body.

Table 2 shows the results of observing the degree of increase in ventilation resistance by actually using a diffuser using a two-layer mesh cloth according to the present invention in a sewage treatment plant. For comparison, this table also shows the test results for a diffuser using a conventional sintered body.

  As can be seen from Table 1, the oxygen dissolution efficiency of the air diffuser according to the present invention is about 1.3 times higher than that of the conventional air diffuser. Further, the initial pressure loss is 4.50 MPa, which is slightly higher than that of the conventional device, but the addition rate of the pressure loss due to long-term use is very small as compared with the conventional device. Therefore, it can be said that the average pressure loss when used in the field is comparable to the conventional apparatus.

The schematic diagram which shows the mode of a deformation | transformation of a mesh cloth when the pressure of the air for aeration acts on a mesh cloth, (a) at the time of aeration stop, (b) represents the state at the time of aeration. The schematic diagram which shows a mode that the bubble which passed the mesh cloth merges. The schematic diagram which shows the structure of a two-layer type mesh cloth. The schematic diagram which shows the state which sludge adhered to the mesh cloth, and a mode that they are removed by flanking, (a) represents the former, (b) represents the latter. The schematic diagram which shows the structure of the aeration element comprised by attaching a mesh cloth to a flame | frame. The schematic diagram which shows the state which has arrange | positioned the filter to the upstream of the mesh cloth. (A) is a schematic diagram which shows the state which the mesh cloth obstruct | occluded with the dust in supply air, (b) is a schematic diagram which shows the state which caught the dust in supply air with the filter. The schematic diagram which shows the outline | summary of the diffuser by which the filter was accommodated in the connection part of the supply air pipe.

Explanation of symbols

1 ... Mesh cloth,
2 ... Bubbles
3 ... sludge,
5 ... Dust,
11 ... Mesh cloth (first layer),
12 ... Mesh cloth (second layer),
13 ... Frame,
14 ... Aeration element,
15 ... Filter,
16 ... Holder,
17 ... Supply air piping,
18: Filter.

Claims (5)

A diffuser using a mesh cloth in which fibers are woven in plain weave, twill weave, oblique weave, or sousse weave,
The mesh cloth includes a first layer disposed on the back side, and a second layer laminated thereon,
The first layer is made of a polyarylate monofilament, and is composed of a cloth having a wire diameter of 10 to 100 μm, woven with 100 to 1000 mesh, and having an opening size of 5 to 200 μm.
The second layer is made of polyarylate monofilament and is made of cloth having a wire diameter of 30 to 200 μm, woven with 10 to 200 mesh, and having an opening size of 50 to 800 μm.
A diffuser characterized by. The air diffuser according to claim 1 , wherein the first layer and the second layer are integrated by pressure bonding. The air diffuser according to claim 2 , wherein the mesh cloth is attached to the frame by applying a tension of 0.1 N / cm or more. The air diffuser according to claim 3 , wherein the mesh cloth attached to the frame is disposed on an upper surface of a box-shaped holder. The air diffuser according to claim 4 , wherein a filter having a dust trapping particle diameter of 1 to 300 μm is inserted in the holder or in a joint portion between the holder and a pipe for supplying air to the holder. .

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