JPH06200877A - Draining method for settling pond - Google Patents

Abstract

PURPOSE:To make change in water level slow as well as to lower the frequency of operation suspension by obtaining the hourly variation of water level continuously measured, and thereby selecting the combination of respective pumps in such a way that the absolute value of water level shall be the smallest one other than zero when water level is raised. CONSTITUTION:The water level 3 of a scale settling pond 4 to which roll cooling water and the like 3 and rain water and the like 2 flow in, is measured by a level gauge 12. Measured water level signals are inputted to a differential circuit 14 via a signal conversion circuit 13, they are then inputted to a command circuit 15 which selects the combination of a plurality of drain pumps 5 through 11 so as to direct commands, thereafter, so that the respective pumps 5 through 11 are thereby controlled In this case, the hourly variation of water level continuously measured is obtained. As a result, the combination of the respective pumps 5 through 11 is so selected that the absolute value of the hourly variation of water level shall be the smallest one other than zero. By this constitution, the basin can be drained in such a way that the water level of the scale settling pond 4 is kept at a point between the highest water level and the lowest one.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for draining a sedimentation basin using a plurality of drainage pumps in combination.

[0002]

2. Description of the Related Art Generally, the following method is used as a drainage method for a sedimentation basin such as a scale pit in a continuous casting factory or a hot rolling factory in the steel industry. The first method is to divide it into multiple zones according to the depth of the scale sedimentation basin, and allocate one to multiple drainage pumps to each zone to indicate that the water level reached a certain zone. This is a method of discharging water by operating and operating the allocated drainage pump when it is detected by a meter, and maintaining the water level at an appropriate level. (Less than,
Abbreviated as zone division method. ) For example, one with and divided into 3 zones A, B and C in order from the top the level of scale sedimentation, as shown in FIG. 7, P _A in each zone, P _B, the drainage capacity of the P _C ~ Assign multiple drainage pumps.

The wastewater flows into the scale sedimentation basin and the water level becomes C
Drainage pump P while in zone_CTo drive. Inflow volume
Is the drainage pump P_CThe water level gradually rises above the ability of
The water level that the water level reached from the C zone to the B zone
Drain pump P when the meter detects _CIn addition to P_BIs driven
Then, the water level continued to rise and the water level went from Zone B to Zone A.
When the water level gauge detects that the
Drainage pump P _B, P_CIn addition to P_AIs driven
Be done. As a result, the amount of drainage (P_A+ P_B+
P_C) Is larger, the water level starts to fall, whether it is in the A zone.
To the B zone, and then to the C zone.
Water pump P_ATo stop. At this time, the inflow water is constant
If there is, drainage (P_B+ P_C) More water again
The ranks will start to rise and will repeat the above pattern.
It

As a second method, the actual method is disclosed in Shokai 55-1504.
There is a method using a flow rate adjusting device for pump equipment disclosed in Japanese Patent No. This method involves opening and closing control of a plurality of on-off valves arranged in parallel with the discharge pipe of the pump and on-off valves provided on a bypass pipe that connects the discharge pipe on the pump side of these on-off valves to the liquid storage tank. This is performed by a liquid level detector that detects the liquid level in the tank, and even if the amount of liquid stored in the liquid storage tank is large or small, or if there is fluctuation in the amount of liquid sent to the liquid storage tank, the pump Can be operated continuously without repeating start-up and stop, preventing obstacles such as impeller damage and opening / closing the on-off valve so that even if the amount of liquid sent to the liquid storage tank fluctuates, it always reaches equilibrium with a certain amount of liquid. Since it can be controlled, it is said that the liquid level does not change suddenly and the load fluctuation of the pump due to the fluctuation of the head can be minimized.

As a third method, Japanese Patent Laid-Open No. 04-3413
There is a method based on the technique disclosed in Japanese Patent Laid-Open No. 9. This method is a technology developed as a drive control method for a plurality of pumping pumps in a water supply system having an elevated water tank. It is equipped with two upper and lower water level detection devices in the elevated water tank, and is started and stopped by the upper water level detection device. Among the pumping pumps, at least one pumping pump electric motor is subjected to variable voltage variable frequency power conversion control (hereinafter abbreviated as VVVF control), so that the number of times of starting and stopping the electric motor can be significantly reduced while suppressing the water level fluctuation. Then, it is a method for obtaining the same effect as the first and second methods.

[0006]

In the zone division method such as the first method, the operation and operation range of the drainage pump is fixed in advance by each zone, and the drainage pump of the drainage pump must be reached unless a predetermined water level is reached. It cannot be started or stopped. That is, (a) Even when the inflow water amount is constant, it is rare that the inflow water amount and the drainage capacity of the drainage pump allocated in a certain zone become equal, and the water level fluctuates within a certain zone depending on the magnitude relationship. (B) When the amount of inflow water changes, a large difference occurs with the drainage capacity of the drainage pump in each zone, and the water level fluctuation becomes more severe. Due to such reasons, the number of times of starting and stopping of the drainage pump increases, which causes problems such as damage of the motor of the drainage pump due to thermal stress, damage of the impeller of the drainage pump, and the like.

In the second method, (a) one drainage pump is used to cover the drainage work of the liquid storage tank such as the scale sedimentation basin, so that the maximum flow rate of the inflowing water that fluctuates the capacity of the drainage pump. It is necessary to adjust to the value, and the operating cost of the drainage pump becomes expensive. (B) In order to reduce the operating cost of the drainage pump and prevent damage to the motor, impeller, etc. due to repeated startup and stoppage of the drainage pump, a plurality of on-off valves are provided in parallel with the discharge pipe of the drainage pump. Is controlled to open and close, but if a large amount of suspended substances such as fine powder scale is contained in the drainage of the scale settling basin, the deposition of suspended substances on the on-off valve causes malfunction of the on-off valve, leakage of water, etc. Maintenance is difficult, and the water level control itself and the drainage work itself may become difficult.

The third method is an effective method for saving energy, and significantly reducing the number of times of starting and stopping the motor, but the VVVF control device itself is an expensive device, and VVVF control is performed on a plurality of existing drainage pumps. Equipment,
Replacing a plurality of existing drainage pumps with drainage pumps having a larger capacity and attaching a VVVF control device thereto requires a large amount of investment, and implementation is problematic in this respect.

The present invention has been made in view of the current state of the art as described above, and improves the first zone division method to combine a drainage pump having an appropriate drainage capacity according to the inflow water amount. By selecting, the change of water level becomes gentle without the need for expensive VVVF control device, etc., and the scale sedimentation basin can be operated and stopped less frequently to protect the drainage pump and motor. It is an object to provide a drainage method.

[0010]

The present invention sets a required maximum water level and a minimum water level in a sedimentation pond such as a scale or sand,
A method for draining a sedimentation basin using a plurality of drainage pumps, wherein the water level is continuously measured and the change amount dh / dT of the water level per hour is calculated.
Maintain the water level in the settling basin between the highest and lowest water levels by selecting the combination of drainage pumps that operate so that the absolute value of the change in water level per hour dh / dT is the smallest value other than zero. It is a method of draining sedimentation ponds, which is characterized by draining water as described above.

[0011]

[Operation] When the inflow is clear and constant, selecting a drainage pump is easy, but in the case of a scale sedimentation tank, rainwater, spring water, other cooling water, overflow water from a water treatment system, etc. In addition, it is difficult to accurately grasp the amount of water. Therefore, in the present invention, a combination of drainage pumps having an appropriate capacity is selected from the amount of change in the water level per hour, not from the water level, and the inflow water amount and the drainage amount are balanced as much as possible for stable water level drainage. It is configured as follows.

That is, the water level h is obtained from the inflow water amount Q, the drainage amount Q ', and the cross-sectional area S of the sedimentation basin by the following equation (1). h = (Q−Q ′) / S (1) When the equation (1) is differentiated with respect to time T, dh / dT = (dQ / dT−dQ ′ / dT) / S dQ / dT = S ( dh / dT) + dQ '/ dT (2) In equation (2), the value of dh / dT is positive when the water level rises and is negative when the water level falls, so (dh / dT) Is 0
If you select and operate a combination of drainage pumps that operate so as to be close to, the inflow water amount and the drainage amount will be almost balanced.

However, if (dh / dT) becomes 0, there is a risk of causing a so-called hunting phenomenon in which the drain pump is frequently started and stopped near the upper and lower limits of the set water level, so zero is selected. do not do. Here, the water level control and drainage work of the sedimentation basin shown in FIG. 1 are carried out as follows.

First, the water level 3 is input as a signal from the water level gauge 12, and the change amount dh / dT of the water level per time is calculated by the signal conversion circuits and differentiation circuits 13 and 14. next,
Selection of combination of drainage pumps and operation command circuit 15
Select the combination of drainage pumps that operate according to the inflow volume based on the drainage capacity of each drainage pump. Although there are various selection methods, an example of the idea is shown in a flow chart in FIGS. 5 and 6. Here, FIG. 5 is a flow chart of selection of a combination of drainage pumps operated when the water level change amount dh / dT per hour is positive, that is, when the water level rises, and FIG. 6 is a water level change amount dh per hour. FIG. 10 is a flow chart of selection of a combination of drainage pumps that operate when / dT is negative, that is, when the water level drops.

In the figure, a three-stage drainage pump or three
Combinations of different drainage pumps are P _A , P _B and P respectively.
_It has a drainage capacity of _C and P _A > P _B > P _C. The water level change (fall) per unit time associated with the operation of each of the above drainage pumps or the combination of each drainage pump when the inflow amount is 0 is P _A / S, P _B / S, P _C /
S, and let these be h _A , h _B , and h _C. Naturally h _A ＞
h _B > h _C.

Now, the water level change amount per hour dh / dT
Is positive, that is, when the water level rises, the magnitude relationship between dh / dT and h _A , h _B , h _C is compared from the larger one as shown in FIG. For example, if dh / dT> h _A, if the pump or pump group P _A is selectively operated, dh / d
dT-h _A has the smallest non-zero value, and the water level rising speed becomes the slowest. If dh / dT> h _A , that is, if dh / dT <= h _A, then dh / dT
-H _A <= 0, the water level change speed becomes 0, and hunting of the drainage pump may occur near the predetermined maximum water level, or it drops before the water level change speed becomes negative and the water level reaches the maximum water level. since then begins level change width is small, and since the start and stop frequency results pump is increased more than necessary a pump or pump unit P _a not select operation, then a large h _B to the next h _a dh / DT is compared, and based on the magnitude relationship, the process proceeds to the subsequent steps according to the same criterion as above. The smallest h among h _A , h _B , and h _C
In comparing the magnitude relationship between _C and dh / dT, dh / d
Dh / dT <= h _C instead of T> h _C , in other words dh
When / dT-h _C <= 0, the pump or the pump group P _C is not operated unless the water level is at the upper limit, but when the water level reaches the upper limit, the pump or the pump group P _C is operated and the water level reaches the upper limit. Do not exceed.

Next, when the water level change amount dh / dT per hour is negative, that is, when the water level falls, as shown in FIG.
The magnitude relationship between the absolute value | dh / dT | of dT and the above-mentioned h _A , h _B , and h _C will be compared from the larger one. For example | dh
If / dT |> h _A, that is, −dh / dT> h _A , 0> dh if the pump or pump group P _A is selectively stopped.
/ DT + h _A , that is, the subsequent water level change rate dh / dT +
h _A has the smallest negative value other than 0, and the water level descending speed becomes the slowest. Further, if | dh / dT |> h _A is not satisfied, in other words, if -dh / dT> h _A is not satisfied, 0 <= dh / dT + h _A , and the water level change speed becomes 0, and the drainage pump near the predetermined minimum water level. There is a risk of hunting, or the rate of change of the water level becomes positive and the water level starts to rise before it reaches the minimum water level, so the fluctuation range of the water level becomes small, and as a result, the frequency of starting and stopping the pump increases more than necessary. Therefore, without selectively stopping the pump or the pump group P _A , the next largest h _B and | dh of h _A
/ DT | is compared, and based on the magnitude relationship, the process proceeds to the subsequent steps according to the same criterion as above. In addition, h _A , h _B , h _C
In the comparison of the magnitude relationship between the smallest h _C and | dh / dT |, it is not −dh / dT |> h _C
<= H _C, when the other words 0 <= dh / dT + h C, but the water level does not stop unless if pump or pump unit P _C to the lower limit, the pump is stopped or the pump unit P _C when the water level comes to the lower limit So that the water level does not drop below the lower limit.

As described above, since it is possible to properly select the combination of drainage pumps that operate according to the inflow water amount Q, the water level changes extremely slowly, and as a result, the number of times the drainage pumps are started and stopped Can be significantly reduced compared to the conventional method.

[0019]

Example 1 A case where the drainage method according to the present invention is applied to drainage work of a scale sedimentation basin of a hot rolling mill will be described. The apparatus used is the apparatus shown in FIG. 1, 1 is inflow water (roll cooling water, etc.), 2 is inflow water (rainwater, leakage water, etc.), 3
Is the water level, 4 is a scale sedimentation basin, 5-11 are drainage pumps,
12 is a water level gauge, 13 is a signal conversion circuit, 14 is a differentiation circuit,
Reference numeral 15 denotes a selection of a combination of drainage pumps to be operated and an operation command circuit.

Using the above equipment, the inflow water amount is 11,0
A combination of drainage pumps operated according to the drainage method of the present invention was selected for the case of 00 m ³ / H, and Example 1 was used.
And The water level setting condition at this time is the maximum water level of 4.7.
m, minimum water level 4.3 m, control water level width (P) = 0.4.

Then, drainage work was carried out by the conventional zone classification method shown in FIG. 4 under the same inflow water amount and the same water level setting condition, and Comparative Example 1 was obtained. In Comparative Example 1, drainage work was carried out by the zone division method in the C zone. Further, the maximum water level and the minimum water level in Comparative Example 1 were the upper limit value and the lower limit value of the C zone.

The results obtained at this time are summarized in Table 1, and FIG. 2 is a diagram showing the change of the water level with respect to time in Example 1 and Comparative Example 1 in one to several cycles. Note that FIG.
The solid line indicates Example 1 and the dotted line indicates Comparative Example 1.

[0023]

[Table 1]

The calculation criteria in Table 1 are as follows. dh / dT = (Q−Q ′) / (S × 100 × 60) T _U = (P × 100) / (dh / dT) T _D = (P × 100) / (dh / dT) T _T = T _{U + T D D = (24} × 60) / T T where dh / dT: amount of change in the water level per unit time Q: inflow water amount ^{(m 3 / H) Q '} : amount of waste water, ie a combination total wastewater drainage pump ( m ³ / H) S: area of the base of the scale sedimentation (310m ²⁾ P: management level width (m) (= the set maximum water level - the set minimum water level) T _U: the water level is raised by the width P of the management level the required time (min) T _D: time required for the water level drops by the width P of the management level (min) T _T: rise of water level, one cycle duration of the drop (minutes) D: 1 day drainage pump Number of times of starting and stopping (time /
Day) ○: Operated drainage pump ×: Stopped drainage pump In addition, the drainage capacity of each drainage pump (A), (B),
(C) and (D) show each zone name of the conventional method.

As is clear from Table 1 and FIG. 2, according to the drainage method of the present invention, the number of times D of starting and stopping the drainage pump per day can be reduced to about 1/4 of that of the conventional method. It can be seen that it has a great effect on the protection of the motor.

[0026]

[Embodiment 2] When the inflow water amount Q is 8,000 m ³ / H, the same equipment as in Embodiment 1 is used to select a combination of drainage pumps that operate according to the drainage method of the present invention. And At this time, the water level was set to a maximum water level of 4.3 m, a minimum water level of 4.0 m, and a control water level width (P) = 0.3.

Then, under the same inflow water amount Q and the same water level setting conditions, drainage work was performed by the drainage pump arrangement according to the conventional zone division method (by the D zone) shown in FIG. The results at this time are summarized in Table 1, and a diagram showing changes in water level with respect to time in Example 1 and Comparative Example 2 in one to several cycles is shown in FIG. In FIG. 2, the solid line shows Example 2 and the dotted line shows Comparative Example 2.

The calculation criteria and the like in Table 1 are exactly the same as in Example 1. As is clear from Table 1 and FIG. 3, according to the drainage method of the present invention, the number of times D of starting and stopping the drainage pump per day can be reduced to about 1/10 or less of the conventional method, and the drainage pump and the motor can be reduced. It can be seen that it has a great effect on the protection of. Further, in Comparative Examples 1 and 2, the inflow water amount Q (each 11,000 m ³ / Hr and 8,000 m ³ / Hr)
In view of the balance between the drainage capacity of the drainage pump and the drainage capacity assigned as shown in FIG. 4, the water level changes in the C zone and the D zone, respectively. D zone lower limit), maximum water level is 5.0
Since it is possible to set m (B zone upper limit) to the management water level width P of 1 m, for example, the effect of the present invention is further enhanced in that case.

That is, when P is 1.0 m, the required time T _T (minutes) for one cycle of rising and falling is when the inflow water amount is 11,000 m ³ / H and 8,000 m ³ / H.
In this case, both of them are about 155 minutes, and the number of times D of starting and stopping the drainage pump per day can be further reduced to about 9.3 times / day.

[0030]

As described above, according to the drainage method of the present invention,
As the water level changes gradually, the number of times of starting and stopping the drainage pump and motor can be greatly reduced compared to the conventional method in order to protect the drainage pump and motor.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing the arrangement of drainage pumps and the like of the apparatus used in the examples.

FIG. 2 is a diagram showing changes in the water level with respect to time in Example 1 and Comparative Example 1 in one cycle to several cycles of rising and falling.

FIG. 3 is a diagram showing changes in the water level with respect to time in Example 2 and Comparative Example 2 in 1 to several cycles.

FIG. 4 is a schematic configuration diagram showing zone division and allocation of drainage pumps and the like in a conventional zone division method.

FIG. 5 is an example of a flow chart for selecting a combination of drainage pumps to be operated when the amount of change in water level per hour dh / dT is positive, that is, when the water level rises.

FIG. 6 is an example of a flow chart for selecting a combination of drainage pumps to be operated when the amount of change in water level per hour dh / dT is negative, that is, when the water level drops.

FIG. 7 is a schematic configuration diagram showing zone division and a drainage pump operating condition in a conventional zone division method.

[Explanation of symbols]

1 Inflow water (roll cooling water, etc.) 2 Inflow water (rainwater, water leakage, etc.) 3 Water level 4 Scale sedimentation tank 5 Drain pump (1,500 m ³ / H) 6 Drain pump (3,200 m ³ / H) 7 Drain pump ( 1,500m ³ / H) 8 Drain pump (1,500m ³ / H) 9 Drain pump (2,500m ³ / H) 10 Drain pump (2,500m ³ / H) 11 Drain pump (2,500m ³ / H) ) 12 Water level meter 13 Signal conversion circuit 14 Differentiation circuit 15 Selection of combination of operating drainage pumps and operation command circuit

Claims (1)

[Claims] 1. A method for draining a settling basin such as a scale or sand by setting a required maximum water level and a required minimum water level, and using a plurality of drainage pumps. The amount of change per hour (dh / dT) is calculated,
When the water level rises and falls, a combination of drainage pumps is selected that operates so that the absolute value of the change in water level per hour (dh / dT) is the smallest value other than zero, and the water level in the sedimentation pond is selected. The method for draining a sedimentation pond is characterized by draining water so that the water is maintained between the highest water level and the lowest water level.