JPS6232998B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aeration device installed in an aeration tank and used for purifying sewage. Conventionally, such aeration devices include those that diffuse compressed air into the water, those that mechanically stir the water surface, and those that create a flow of water in the water using mechanical means and supply compressed air. The format is known. Recently, in order to save energy, aeration devices that use large-capacity, low-head axial flow pumps are often used as a means of creating a flow in water. This type of aeration device is shown in FIG. An impeller 2 is rotatably attached to the rotating shaft of the underwater motor 1, and a casing 3 fixed to the underwater motor 1
The motor is equipped with a suction port 4 below the impeller and a discharge port 5 that opens over the entire circumference in a direction substantially perpendicular to the motor axis above the impeller. Aeration ports 6, 7 are provided on the upstream side or the downstream side of the impeller and are connected to a gas source (not shown) via a gas conduit 8 to supply oxygen-containing gas. Such an aeration device is installed in the aeration tank. Therefore, the rotation of the impeller 2 driven by the underwater motor 1 sucks the treated flow in the aeration tank through the suction port 4, and mixes it with the oxygen-containing gas supplied from the aeration port 6 or 7. They are mixed and stirred to become a gas-liquid multiphase flow and are discharged from the discharge port 5 in the horizontal direction over the entire circumference. However, in such an aeration device, the gas-liquid multiphase flow discharged from the discharge port changes into an upward flow due to the buoyancy of the bubbles, and then gathers above the aeration device to form a flow that reaches the water surface. As a result,
A large difference in apparent density occurs between the upper part of the aerator and its surroundings, and a simple, large-scale density flow is formed that rises above the aerator and descends around it.
For this reason, the bubbles quickly reach the water surface because the rising speed due to the density flow is added to the rising speed due to their own buoyancy, and the residence time of the bubbles is significantly reduced.
Furthermore, since the bubbles are concentrated in a narrow area, the bubbles often coalesce, increasing the bubble diameter, which also reduces the bubble residence time. Due to these causes, the oxygen utilization efficiency (the ratio of dissolved oxygen to the oxygen contained in the supplied gas) has been reduced. In addition, since the discharge flow is uniformly discharged radially in all directions from the discharge port of the aeration device, the flow velocity after discharge decreases approximately in inverse proportion to the square of the distance from the discharge port. The drawback was that the stirring and oxygen dissolving abilities were reduced. For example, JP-A No. 125967-125967 and JP-A-Sho 50
Japanese Patent No. 126574 discloses an aeration device that has an impeller in the center and discharges a multiphase flow of gas and liquid over the entire circumference in a substantially horizontal direction. However, in this known technique, a plurality of plate-shaped guide vanes are provided radially outward of the impeller, so the flow exiting the impeller collides with the plate-shaped guide vanes, causing solid matter and The air bubbles are separated and discharged in a uniform flow over the entire radial outer circumference of the impeller. For this purpose, the flow pattern is essentially the same as that of the prior art described with reference to FIG. 1, and therefore has similar disadvantages. Therefore, an object of the present invention is to provide an aeration device that can lengthen the residence time of bubbles and improve stirring and oxygen dissolution capabilities. According to the present invention, in an aeration device having an impeller and discharging a multiphase flow of gas and liquid over the entire circumference in a substantially horizontal direction after mixing gas and liquid in a casing, the discharge portion of the aeration device has an impeller. A barrier is provided to partially block the multiphase flow and divide the multiphase flow into a plurality of discharge flows. The multiphase flow from the impeller is therefore partially blocked by the barrier, so that the discharge flow is partially blocked. For this reason, the multiphase flow pressurized by the impeller is discharged from a place without a barrier in the form of a jet at a relatively high speed, accompanied by the liquid in the dead zone between each jet, so that it can be discharged horizontally. Reach far in a direction. As a result, the horizontal mixing action is performed well, and the range in which the bubbles spread can be expanded.
Furthermore, since the bubbles are not concentrated, the rising speed of the bubbles is slowed, the residence time is increased, and the oxygen utilization efficiency is improved. In the practice of the present invention, the barrier may be provided integrally with the discharge portion, may be provided on the cover, or may be provided on the bottom surface of the aeration tank. This barrier is preferably 10-50% of the total horizontal circumference. Embodiments of the present invention will be described below with reference to FIGS. 2 to 11. 2 and 3 show a first embodiment of the present invention, which has the same structure as the aeration device shown in FIG. 1 except for the points described later, and has legs 9 on the bottom of the aeration tank.
It is installed by. A barrier 10 is integrally provided at the discharge port 5 of the aerator casing 3,
This barrier 10 prevents the discharge of the discharge flow. The number of barriers 10 can be selected as appropriate, and providing them in the center is effective in uniformly mixing the inside of the aeration tank. Further, it is desirable that the total visual angle θ of the barrier 10 viewed from the center of the aeration device is 10 to 50% of the entire circumference. FIG. 9 shows the change in oxygen utilization efficiency when the ratio of the barrier 10 is changed, and it can be seen that a high oxygen utilization efficiency is maintained when the barrier 10 is in the range of 10 to 50%. In this way, by providing the barrier 10 at the discharge port 5 and forming an area where there is no discharge flow, the deceleration of the discharged flow is much smaller than in the conventional case where no barrier is provided, and the discharge flow is spread far away in the horizontal direction. reach up to
As a result, horizontal mixing is improved and the range in which the bubbles spread is expanded. For this reason, the air bubbles are not concentrated in a small area of the aeration tank, and the formation of a simple, large-scale density flow is prevented, and the rising speed of the air bubbles is not accelerated by the density flow, so the air bubbles remain. This increases the time and reduces the coalescence of bubbles, improving oxygen utilization efficiency. 4 to 6 show a second embodiment of the present invention, in which the barrier was provided integrally with the discharge part in the previous embodiment, but in this embodiment, it is detachably attached to the aeration device. The cover is provided with a barrier that divides the gas-liquid multiphase flow discharged from the discharge portion into a plurality of discharge flows. That is, in Figure 4, 1
1 is a cover that is removably attached to the aeration device,
It consists of a flat plate 12 and a barrier 10a depending from the flat plate 12. By mounting this cover 11 on the aeration device as shown in FIG.
a divides the gas-liquid mixed flow discharged from the discharge port 5 into a plurality of discharge flows. Further, as shown in FIG. 6, the barrier 10b is curved toward the center.
By doing so, it acts as a guide plate and can smoothly divide the discharge flow. Curving the barrier in this way is of course also effective in the first embodiment described above. FIG. 7 shows a third embodiment of the present invention, in which a barrier 10c is provided at the bottom of an aeration tank in which an aeration device is installed. The barrier 10c serves as a guide for installing the aeration device. In addition, in the case of a bottom discharge type aeration device where the water flow flows from top to bottom, the eighth
A barrier 10d may be provided at the bottom of the aeration tank as shown in the figure as a fourth embodiment. Experiments were conducted in an aquarium with a circumference of 8 m x 8 m and a water depth of 5 m under the conditions shown in the following table, and the results shown in the following table were obtained.

[Table] From the results of this experiment, it was revealed that in the case of the present invention, the overall mass transfer capacity coefficient Kca was larger and the oxygen utilization efficiency was higher than in the case of the conventional case in which no barrier was provided in the discharge section. As explained above, although the present invention has a simple structure, it has the following excellent effects. Oxygen utilization efficiency is greatly improved. Energy consumption is significantly reduced. Air bubbles can be spread over a large area of the aeration tank. The entire aeration tank can be stirred with average mixing intensity. Det space is reduced. Although the above description has mainly been given to a top discharge type aeration device in which a water flow flows from the bottom to the top, the present invention can of course also be implemented in a bottom discharge type aeration device in which a water flow flows from the top to the bottom. An example is Figure 10 and Figure 1.
This is shown in Figure 1. The fifth embodiment shown in FIGS. 10 and 11 is
This is a specific example of the bottom discharge type as shown in FIG. That is, a streamlined barrier 10c facing the flow is provided integrally with the casing 3 near the discharge port 5, and the flow can be smoothly divided by this barrier 10c. Furthermore, the pump is not limited to an axial flow pump, but may also be a mixed flow pump or a centrifugal pump, and the motor that drives the pump is not limited to a submersible motor; for example, the motor may be installed outside the tank,
A pump may also be driven. Furthermore, in addition to the barrier, providing a planar guide plate in the discharge section that roughly matches the width of the discharge flow to allow the discharge flow to reach as far as possible without slowing down will improve oxygen utilization efficiency. Effective for measurement.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an example of an aeration device in which the present invention is implemented. FIGS. 2 and 3 show a first embodiment of the present invention, with FIG. 2 being a perspective view of the aeration device and FIG. 3 being a cross-sectional view. Figures 4 to 6
The figures show a second embodiment of the invention, FIG. 4 is a perspective view of a cover with a barrier, FIG. 5 is a perspective view of an aeration device with the cover attached, and FIG. 6 is a modification of the cover with a barrier. FIG. 3 is a perspective view of an example. FIGS. 7 and 8 are perspective views of aeration devices showing third and fourth embodiments of the present invention, respectively. FIG. 9 is a graph showing the relationship between barrier ratio and oxygen utilization efficiency. 1st
0 is a plan view of a casing according to a fifth embodiment of the present invention, and FIG. 11 is a sectional view of FIG. 10. DESCRIPTION OF SYMBOLS 1... Underwater motor, 2... Impeller, 3... Casing, 4... Suction port, 5... Discharge port, 6, 7... Diffusion port, 8... Gas conduit, 9... Leg, 10, 10a, 10
b, 10c, 10d...Barrier, 11...Cover, 12
...flat plate.

Claims (1)

[Claims] 1. In an aeration device having an impeller and discharging a multiphase flow of gas and liquid over the entire circumference in a substantially horizontal direction after mixing gas and liquid within a casing, the discharge portion thereof An aeration device comprising a barrier that blocks a portion of the multiphase flow and divides the multiphase flow into a plurality of discharge flows. 2. The device according to claim 1, characterized in that the discharge section is provided with a barrier that divides the gas-liquid multiphase flow discharged from the discharge section into a plurality of discharge flows. Aeration equipment. 3 A cover that is removably attached to the aeration device,
2. The aeration device according to claim 1, further comprising a barrier that divides the gas-liquid multiphase flow discharged from the discharge portion into a plurality of discharge flows. 4. Claim 1, characterized in that a barrier is provided on the bottom of the aeration tank in which the aeration device is installed, which divides the gas-liquid multiphase flow discharged from the discharge section into a plurality of discharge flows. Aeration equipment as described in section.