JPH03202200A - Deep shaft and its operation - Google Patents

Abstract

PURPOSE:To prevent accumulation of sand, etc., and save energy by periodically driving a deep shaft having an area ratio of SD/SR satisfying the relation, 1/20<=SD/SR<=1/4, where SD is a down commer cross section and SR is a riser cross section in waste water treatment of raw water having BOD at most 200mg/l. CONSTITUTION:A deep shaft is applied to raw water having low BOD at most 200mg/l and having an area ratio of SD/SR satisfying the relation, 1/20<=SD/SR<=1/4, where SD is a down commer cross section and SR is a riser cross section. At the time of reverse driving, air supply to a riser gas spraying tube 4 is stopped. Owing to inertia of a liquid, regular circulation (a) continues for a moment but soon it turns to a reverse circulation (b) by blowing air from the down air spraying tube 5. This reverse operation period is carried out during night when load is low and normal operation is carried out during day time when load is high. In this way, necessary air supply amount is decreased and energy saving is achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a deep shaft applied to the treatment of low-concentration sewage and a method of operating a debenyaft relating to intermittent reverse circulation operation.

[Prior Art] FIG. 3 shows a schematic configuration of a conventional deep shaft. In the figure, 1 is the outer cylinder of the deep shaft, 2 is the inner cylinder, and 3
is a head tank, 4 is a riser diffuser pipe for generating a circulation flow, 5 is a down diffuser pipe for blowing aeration air, 6 is a passage between the outer cylinder 1 and the inner cylinder 2, that is, a riser, and 7 is a riser pipe. This is a passage within the inner cylinder 2, that is, a downcomer.

In the deep shaft described above, when raw water is supplied and air is first blown into the riser 6 from the riser diffuser 4 several tens of meters below the ground, a circulating flow is formed as shown by the arrows due to the air lift effect.

After the circulating flow is stabilized, air is then blown into the downcomer 7 through the down diffuser 5. At this time, since the descending velocity of the bubbles is greater than the ascending velocity of the bubbles, the bubbles are drawn to the bottom of the deep shaft, reverse, and rise inside the riser 6.

The difference in porosity (ratio of gas portion in the liquid) between the downcomer 7 and the riser 6 causes an apparent difference in specific gravity, and the circulating flow is maintained, resulting in steady circulation.

In deep shaft operation, the downward flow velocity VD is (1> (2) VD≧1.2m/see, and the upward flow velocity VR is VR≧0.7.
Standards are set to maintain m/see. These reference values are for the need to entrain air bubbles in the case of a downward flow velocity, and to prevent sand, stones, etc. from accumulating at the bottom of the deep shaft in the case of an upward flow velocity. In this case, the area ratio of the downcomer cross-sectional area S to the riser cross-sectional area SR is usually designed to be 1:1.5-3.

[Problems to be Solved by the Invention] However, in treating sewage such as low-concentration sewage, an operating method in which the amount of air required for circulation exceeds the amount of air required for oxygen supply wastes energy.

Therefore, one possible solution in such a case is to reduce the cross-sectional area of the inner cylinder 2. For example, S:S
−1:9 design.

R According to this method, since the circulation flow rate of the downcomer 7 is reduced, the amount of air required for circulation can be reduced.

However, as the downward flow velocity V, the minimum VD-1,2
m/see, then the rising flow velocity vR-0,13
m/see, which no longer satisfies the above standard value, and it becomes impossible to prevent the accumulation of sand, etc.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a deep shaft that can be applied to the treatment of low-concentration sewage and that can be operated in an energy-saving manner while preventing the accumulation of sand and the like, and its operating method.

[Means for Solving the Problems] In order to achieve the above object, the deep shaft according to the present invention has a low concentration of raw water with a BOD (biochemical oxygen demand) of 200 mg/ρ or less. Moreover, the area ratio of the downcomer cross-sectional area SD to the riser cross-sectional area SR is set as follows: 1/20≦SD/5R51/4.

Further, the deep shaft operating method according to the present invention is such that the deep shaft having the above configuration is operated in normal operation with normal circulation during periods of high load, and intermittently operated with reverse circulation during periods with low load. (3) (4).

[Function] As mentioned above, reducing the downcomer cross-sectional area SD reduces the descending flow rate, so the amount of air required for circulation can be reduced. At this time, if an attempt is made to suppress the required downward flow velocity VD to the minimum VD-1 or 2 m/sec, the upward flow velocity VR no longer satisfies the reference value as the riser cross-sectional area SR increases.

Therefore, during periods of high load, for example during the day, normal operation is performed, that is, normal circulation operation in which the flow direction of the liquid is downward in the downcomer and upward in the riser. As a result, the upward flow velocity (1) becomes low as described above, and it is inevitable that sand and the like will accumulate at the bottom of the deep shaft. In order to remove such deposits, it is convenient to perform a reverse circulation operation in which the flow direction of the liquid is opposite to the upward direction, since the amount of air blown in can be reduced. Therefore, reverse circulation operation is performed during low load periods, for example at night. However, since the reverse circulation operation is performed only for the purpose of removing sediment, the upward flow velocity in this case is vR-0.7 m/sec.
An amount of air sufficient to satisfy e is sufficient, but if this reverse circulation operation is continued, the inside of the deep shaft will become anaerobic, so it may be performed intermittently for about 2 to 3 hours at night.

Therefore, since the deep shaft to which the present invention is applied is intended to reduce the amount of air supplied,
Regarding raw water with an OD of 200■/ρ or less, the area ratio of the downcomer cross-sectional area SD to the riser cross-sectional area Sp is in the range of 1/20≦S o / S R ≦1/4. Appropriate.

When the SD/SR ratio exceeds 1/4, the amount of air required for circulation increases, while when it is less than 1/20, even if the downward flow velocity V satisfies the standard value, there will be an overall lack of oxygen, so eventually This is because the amount of air for aeration increases, and in either case, the energy saving effect of the present invention is lost.

[Embodiment] Fig. 1 is a block diagram of a deep shaft according to the present invention, and Fig. 2 is a cross-sectional view thereof. The components (5) and (6) are the same as in Figure 3 showing the conventional example, so they are designated by the same reference numerals.

The flow of liquid during normal operation is shown by a solid arrow a, and that during reverse operation is shown by a broken line. Also, during reverse operation, the air supply to the riser diffuser pipe 4 is stopped. Then, the normal circulation a continues for a while due to the inertia of the liquid, but soon the air is blown from the down diffuser pipe 5, causing the liquid to reverse and circulate in the opposite direction. This reverse drying period lasts for 2 to 3 hours during the night when the load is low, and normal operation is performed during the day when the load is high.

Next, in the case of raw water concentration BOD-100■/jll, the cross-sectional area ratio of downcomer 7 and riser 6 is S /S
And DI of descending flow velocity vD-1,2m/see? Table 1 shows the relationship between the rising flow velocity V R and the air amount reduction rate (during normal operation).

Table 1 Also, during reverse operation, the air supply amount can be further reduced, so the air amount reduction rate shown in Table 1 is further reduced.

By performing reverse circulation, the upward flow velocity in the downcomer 7 satisfies the standard value (0.7 m/see), so that sand, stones, etc. accumulated at the bottom of the deep shaft can be discharged.

[Effects of the Invention] As described above, according to the present invention, the deep shaft is configured to be applied to low-concentration sewage treatment and the area ratio of the downcomer area SD to the riser cross-sectional area SR is within a predetermined range. , it becomes possible to reduce the amount of air supply required for circulation, resulting in energy savings.

(7> (8) In addition, by operating such a deep shaft normally during periods of high load and intermittently performing reverse circulation operation during periods of low load, it is possible to achieve energy-saving operation and reduce the amount of deposits at the bottom of the deep shaft. can be eliminated.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of a deep shaft according to the present invention, FIG. 2 is a cross-sectional view of FIG. 1, and FIG. 3 is a configuration diagram of a conventional deep shaft. 1... Outer cylinder 2... Inner cylinder 3... Head tank 4... Riser diffuser pipe 5... Down diffuser pipe 6... Riser 7... Downcomer

Claims (2)

[Claims] (1) Applicable to low-concentration wastewater treatment with a raw water concentration of 200 mg/l or less in BOD, the area ratio of downcomer cross-sectional area S_D to riser cross-sectional area S_R is 1/20≦S_D/S_R≦ 1/4 deep shaft. (2) A method for operating a deep shaft according to claim 1, wherein the deep shaft is operated in normal operation with regular circulation during periods of high load, and intermittently operated with reverse circulation during periods of low load.