JP3239172B2 - Axial impeller in stirring aerator and method of operating stirring aerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stirring aeration apparatus used for treating sewage and sludge such as sewage and human waste, and more particularly, to an improvement of an axial impeller in the apparatus, and further to the operation of the stirring aeration apparatus. It is about the method.

[0002]

2. Description of the Related Art As one method for aerobically treating sewage or the like with activated sludge, as shown in FIG. 1, a draft tube (5) vertically arranged in a treatment tank (4) and a draft tube (5) and is driven by the motor (1)
An axial impeller (6) rotated through (2); an air diffuser (3) arranged below the axial impeller (6) and connected to a blower (8); and an air diffuser (3). Rectifying member arranged under
(7) Using an agitating aeration device equipped with
(6) forms a downward flow in the draft tube (5),
There is a stirring and aerating method in which air is blown into this to agitate the liquid to be treated while agitating the liquid.

The axial impeller of the stirring aeration apparatus used in this method has been studied. In order to prevent the fibers from being entangled in the sewage due to stirring, each blade (9) is required to rotate in a half-turn direction from the centrifugal direction. Angularly inclined (i.e., retracted) axial impeller (Japanese Patent Laid-Open No. 60-227821).
Boss ratio is increased to prevent vibration or backflow (flooding) of large bubbles to the suction side, and a small disc-shaped centrifugal impeller is installed under the axial impeller to disperse bubbles. Stirring device (Japanese Unexamined Patent Publication No.
No. 253592) is known.

[0004]

The impeller (16) of such a conventional stirring aeration apparatus is a two-dimensional impeller (impeller having a constant angle of attack) as shown in FIG. Therefore, it is desirable that the strength of the water flow in the axial direction at the time of stirring is uniform at an arbitrary position in the radial direction of the impeller, but the water flow is strong on the outer peripheral side of the impeller and extremely weak on the side near the boss. Imbalance occurs sideways. As a result, bubbles accumulate around the boss below the propeller, causing backflow of the bubbles (flooding), vibration, noise, and the like. Excessive discharge of the generated bubbles from the inside of the draft tube is excessive. It is necessary to use power to further increase the rotation speed and increase the amount of downward water, and because the effective working area of the impeller is small, a large-diameter (for large-capacity) impeller is required compared to the amount of water. Yes, it is difficult to operate the equipment efficiently and stably.

SUMMARY OF THE INVENTION In view of the foregoing, an object of the present invention is to set the thickness of the trailing edge of the blade to a very low range and adjust the frequency of the vortex generated at the trailing edge, thereby effectively miniaturizing the bubbles and reducing the bubbles. It is an object of the present invention to provide an axial impeller of a stirring and aerator and an operation method of the stirring and aerator capable of solving the problems of backflow flooding, vibration, noise and the like.

[0006]

An axial impeller according to the present invention comprises a draft tube (5) vertically arranged in a processing tank (4), a draft tube (5), and a motor (1). ) Through the drive shaft (2), and an air diffuser (3) arranged below the axial impeller (6) and connected to the blower (8). In a stirring and aerating apparatus provided with a rectifying member (7) disposed below the trachea (3), the trailing edge thickness (t) of the plurality of wings (9) constituting the axial impeller (6) is determined by the diameter of the impeller. of 0.0265 to 0.6
563 %.

Further, the present invention uses the axial-flow impeller having the above-described configuration, and operates at an impeller outer peripheral speed of 5 to 15 m / sec.
A method for operating a stirring / aeration apparatus, wherein the vortex frequency at R is adjusted to a range of 4000 to 6000 Hz.

Preferably, the blades (9) of the axial impeller (6) are airfoil cross-section blades or circular cross-section blades.

[0009]

In the axial impeller according to the present invention, since the trailing edge thickness (t) of the plurality of blades (9) constituting the axial flow impeller (6) is within the above range, the high frequency vortex is generated at the trailing edge of the blade (9). Occurs.
Therefore, bubbles can be miniaturized by the high frequency vortex. Further, since the frequency of the vortex exceeds the forced vibration range generated in the drive system, the problem of noise and vibration can be solved, and a noise reduction effect can be exhibited.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is an overall view showing an example of a stirring and aerator. The stirring and aeration device is a draft tube (5) vertically arranged in the treatment tank (4), and is positioned in the draft tube (5) and rotated by a motor (1) via a drive shaft (2). An axial impeller (6), and an air diffuser (3) disposed below the axial impeller (6) and connected to the blower (8);
A rectifying member (7) arranged below the air diffuser (3). Using this apparatus, a downward flow is formed in the draft tube (5) by the axial flow impeller (6), and air is blown into the downward flow to diffuse the liquid to be treated while treating the liquid with the treatment tank (4). The mixture is circulated and stirred in). Air blower (8)
As a result, the air which is sent into the diffuser (3) and flows out of the diffuser is sheared by the downward flow caused by the rotation of the axial impeller (6) to become fine bubbles.

The microbubbles are guided to the bottom of the tank together with the downward flow in the draft tube (5). When the fine bubbles rise outside the draft tube (5) from the bottom of the tank, an upward flow is generated in the liquid around the bubbles. Tightening and facilitating the circulation of liquid in the treatment tank (4).

The axial impeller (6) has three blades (9),
It is a low-lift, large-capacity, small-power machine that can obtain a large stirring force.

The air diffuser (3) is provided below the axial impeller (6) and blows air at right angles to the downward water flow.

The draft tube (5) has an inside diameter substantially equal to the diameter of the axial impeller, guides the liquid to be treated and bubbles to the bottom of the tank, increases the stirring power at the bottom, and increases the efficiency of dissolving air.

The rectifying member (7) is for efficiently converting the spiral flow formed by the axial impeller (6) in the draft tube (5) into a downward flow.

Since the stirring mechanism and the aeration mechanism are independent of each other in the stirring aeration apparatus having this structure, the stirring intensity and the oxygen supply amount can be controlled independently.

FIGS. 2 and 3 show an example of the trailing edge structure of the axial impeller according to the present invention. Axial impeller
The wing (9) of (6) has a washback (11) below the leading edge. In this example, the conventional wing (the impeller radius and wing width are the same as those in FIG. 2; trailing edge thickness = 4.5 mm) (16) is cut off to form the inclined surface (12) shown in FIG. And
The trailing edge thickness was set to 0.5 mm by forming this inclined surface.

FIG. 4 shows another example of the trailing edge structure of the axial impeller according to the present invention. In this example, the upper surface of the conventional wing (having the same dimensions as above) (16) shown in FIG. 0.5 mm.

FIG. 5 is a graph showing the relationship between the rotational speed and the AHC (maximum supply air amount) efficiency for the conventional impeller shown in FIG. 7 and the axial impeller according to the present invention shown in FIGS. .

FIG. 5 shows that the impeller according to the present invention has a higher AHC efficiency, that is, a higher air dissolution amount in water than the conventional impeller (the flow rate hardly changes, but the AHC is improved by 10% or more). are doing).

FIG. 6 is a graph showing the relationship between the rotational speed and the noise for the conventional impeller shown in FIG. 7 and the axial impeller according to the present invention shown in FIGS. 2 and 3.

FIG. 6 shows that the impeller according to the present invention has lower noise than the conventional product.

The relationship between the blade radius ratio (r / R), trailing edge thickness (t), and vortex frequency (Hz) is as shown in the table below.

[0025]

[Table 1] The frequency of the forced vibration due to rotation is as follows.

・ Shaft rotation 179/60 = 2.98 Hz ・ Three blades 3 × 179/60 = 8.94 Hz ・ Lower rectifying plate 4 × 3 × 179/60 = 35.7
6Hz-Reducer input shaft 20 sheets x 1750/60 = 583.3
Hz (20 teeth)

The frequency of the vortex generated at the trailing edge (Karman vortex)
Is given by the following equation:

[0028]

(Equation 1) In the operation method of the present invention, the impeller outer peripheral speed is 5 to 15 m /
In seconds, the vortex frequency at 0.7R is 500-6000H
Adjust to the range of z.

In order to adjust the frequency of the vortex with an impeller used at an outer peripheral speed of 5 to 15 m / s, there are two methods of changing the rotation speed (N) and changing the trailing edge thickness (t). There is. When the rotational speed is changed, the power efficiency of the impeller fluctuates remarkably, so that it is limited to the range of the outer peripheral speed (corresponding to the variable speed motor).

In order to generate high-frequency vortices without causing fluctuations in power efficiency and to make bubbles finer and improve oxygen dissolving efficiency, it is necessary to reduce the thickness of the trailing edge blade. In this case, it is preferable to evaluate the vortex frequency at the position of 0.6 to 0.7R.

If the vortex frequency at 0.7R is 500 Hz or less, a resonance phenomenon with the driving portion occurs, which is not preferable. The eddy frequency that can be used more safely to avoid resonance is 1000 Hz or more (at the 0.7R position), and the eddy frequency that can be used more safely is 4000 Hz or more (at the 0.7R position).

Relationship between the impeller rotation speed and the impeller diameter,
Table 2 shows the relationship between the impeller t / D and the vortex frequency of the four impeller diameters.

[0033]

[Table 2] The effective trailing edge thickness for generating a high frequency vortex at D = 1000 mm is as follows.

Under the condition of using the impeller at an outer peripheral speed of 5 to 15 m / s, the peripheral speed at 0.7 R and the trailing edge thickness at each frequency 1) The trailing edge thickness at each radial position (mm)

[0035]

(Equation 2)

[0036]

(Equation 3)

[Table 3] The trailing edge thickness (t) of the wing (9) of the axial impeller (6) is 0.0265 to 5.25% of the impeller diameter, more preferably 0.0265 to 2.625 %, even more preferably 0.025 to 2.625 %.
It is in the range of 265-0.6563 %.

[0037]

According to the present invention, a high-frequency vortex is generated at the trailing edge of the wing (9). Therefore, bubbles can be miniaturized by the high frequency vortex. Further, since the frequency of the vortex exceeds the forced vibration range generated in the drive system, the problem of noise and vibration can be solved, and a noise reduction effect can be exhibited.

As a result, problems such as backflow of air bubbles (flooding), vibration, and noise are solved, and as a result, efficiency and stabilization of processing and power consumption are achieved.

Further, the efficiency of dissolving oxygen in the liquid to be treated can be improved and the power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall view showing an example of a stirring and aerator.

FIG. 2 is a cross-sectional view of a blade showing a structure of an axial impeller.

FIG. 3 is an enlarged view of a main part of FIG. 2;

4 is an enlarged view of a main part corresponding to FIG. 3, showing a structure of an axial impeller.

FIG. 5 is a graph showing a relationship between a rotation speed and AHC efficiency.

FIG. 6 is a graph showing a relationship between a rotation speed and noise.

FIG. 7 is a cross-sectional view of a conventional axial impeller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Motor 2 ... Drive shaft 3 ... Air diffuser 4 ... Processing tank 5 ... Draft tube 6 ... Axial impeller 7 ... Rectifying member 8 ... Blower 9 ... Blade 10 ... Boss noise reduction processing 12 ... Slope 13 ... Slope

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C02F 3/14-3/26 B01F 3 / 04,7 / 16

Claims (2)

(57) [Claims] Claims: 1. A draft tube (5) vertically arranged in a treatment tank (4), and a draft tube (5)
And an axial impeller (6) rotated by a motor (1) via a drive shaft (2); and an air diffuser (3) disposed below the axial impeller (6) and connected to a blower (8). ) And the diffuser
(3) a rectifying member (7) disposed below the agitating and aerating device, and a plurality of blades constituting an axial impeller (6).
(9) The trailing edge thickness (t) is 0.0265 of the impeller diameter.
An axial impeller in a stirred aeration apparatus characterized by being in the range of 0.6563 %. 2. A stirring and aerator according to claim 1, wherein the vortex frequency at 0.7R is adjusted to a range of 4000 to 6000 Hz at an impeller outer peripheral speed of 5 to 15 m / sec. how to drive.