JPH0333395B2 - - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention is directed to improving the quality of purified water by suppressing fluctuations in the flow rate of wastewater returned to the receiving well during filter cleaning. This relates to a control device.

(Prior Art) Figure 5 shows a general process configuration of a water purification plant. In the same figure, raw water 1 arrives at landing well 2,
Water is normally supplied to a consumer 6 via a settling tank 3, a filtration tank 4, and a water purification tank 5.

When cleaning the filtration basin 4, water for cleaning is supplied from the water purification basin 5 to the filtration basin 4, and the cleaning wastewater flows into the drainage basin 8, and is returned to the receiving well 2 by the return pump 9 to be reused. Ru.

(Problems to be Solved by the Invention) Conventionally, the water level h of the drainage pond 8 is detected by the water well gauge 12, and a target value of the wastewater return flow rate at which the water level h becomes constant is determined.
Amount of wastewater returned by applying Q _r and detected by flow meter 11
The flow rate adjustment valve 10 is controlled via the flow rate control device 7 by feeding back Q _b , but when cleaning the filtration basin, the amount of wastewater returned Q _b increases, and as a result, an excessive amount of wastewater is returned to the landing well 2. There is a problem that the quality of purified water deteriorates.

The present invention has been made to solve the above problems, and aims to provide a wastewater return flow rate control device for a water purification plant that can obtain appropriate water quality while limiting the water level in a drainage pond to an allowable range. .

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a water level tracking means for storing the water level of a drainage pond in correspondence with time, and an extreme value detection means for detecting the extreme value of the water level of the drainage pond based on the stored value. , a condition setting means for setting the cleaning cycle of the filtration basin and the permissible limit of the water level of the drainage basin, a control parameter calculation means provided according to the fluctuation range of the wastewater return flow rate, and the outputs of the extreme value detection means and the condition setting means. , or a flow rate target value calculation means for calculating a wastewater return flow rate target value based on each output obtained by adding a control parameter calculation means to the control parameter calculation means.

(Operation) In this invention, the extreme value detection means detects the extreme value of the drainage pond water level based on the water level data of the drainage pond stored in the water level tracking means, and further calculates the control parameters based on the detected extreme value. While the means calculates the control parameters, the condition setting means sets the cleaning cycle of the filtration basin and the permissible limit of the water level of the drainage basin, and the flow rate target value calculating means calculates the wastewater return flow rate based on the detected extreme value and set value. Either a target is calculated, or a wastewater return flow rate target value is calculated based on the detected extreme value, set value, and control parameters, and the wastewater return flow rate is controlled in accordance with this wastewater return flow rate target value.

(Embodiment) Fig. 1 is a block diagram showing the configuration of an embodiment of the present invention together with the process of a general water purification plant. Showing the same element.

Here, raw water 1 arrives at a receiving well 2, and normally passes through a settling tank 3, a filtration tank 4, and a water purification tank 5 before reaching a demand destination 6.
is supplied to Furthermore, when cleaning the filtration basin 4, the water in the water purification basin 5 is returned to the filtration basin 4, and the washed wastewater used for cleaning flows into the drainage basin 8, and further, the water from the water receiving well 2
returned to and reused.

Incidentally, a flow rate control device 7 and a cleaning control device 13 are provided to suppress changes in the flow rate of waste water returned to the landing well 2 during this cleaning process.

Of these, the flow rate control device 7 controls the return pump 9 based on the respective outputs of a water level meter 12 that detects the water level h of the drainage pond 8, a flow meter 11 that detects the wastewater return flow rate, and a flow rate target value calculation means 24, which will be described later. and controls the flow rate adjustment valve 10.

Further, the cleaning control device 13 controls the flow rate adjustment valve and pump to supply the water necessary for cleaning to the filter basin 4 based on the outputs of the water level gauge 12 and the condition setting means 25, but the detailed control contents are as follows. Since it is not directly related to the present invention, the explanation will be omitted.

On the other hand, in order to calculate the above-mentioned wastewater return flow rate target value Q _r , a control device 20a using an electronic computer
is used. This control device 20a includes a water level gauge 1
a water level tracking means 21 for storing the water level of the drainage pond 8 detected by the drain pond 8 for a period of, for example, about 1.5 times the cleaning cycle;
The extreme value detecting means 22 calculates the maximum value H _nax of the drainage water level from the stored value, and the extreme value detected by the extreme value detecting means 22, the cleaning cycle of the condition setting means 25, and the water level of the drainage pond are substituted into a predetermined formula. Return flow rate target value Q _r
The target flow rate calculation means 24 calculates the flow rate target value.

The general operation of this embodiment will be explained below with reference to the flowchart of FIG.

First, in step 100, the memory constituting the water level tracking means 21 and various setting values are initialized. Next, the program moves to the actual control program, and in step 101, the cleaning cycle set value ΔT, the upper limit set value H _high of the drainage pond water level, the lower limit set value H _lpw ,
And read the drainage pond water level h. In step 102, the water level h of the drainage pond is stored in the water level tracking means 21 in order to obtain the change trend of the water level of the drainage pond. The water level tracking means 21 is composed of a shift register that can sequentially shift data according to the following procedure, and stores the water level of the drainage pond for about 1.5 times the cleaning cycle.

for n=1 to N−1 do H(n+1)←H(n); H(1)←h; however H(i): Array configuring shift register N: Size of array H(i) It is.

Next, in step 103, the maximum value of the water level of the drainage pond is determined by the extreme value detection means 22. In this case, the maximum value of the water level of the drainage pond is determined as
H _nax .

H(1)≦H(2) and H(3)<H(2) …(1) H _nax ←H(2) Next, in step 104, the maximum value H _nax of the drainage pond water level obtained in step 103 is determined. Based on this, calculate the wastewater return flow rate target value Q _r using the following formula.

Q _r = (H _nax − H _lpw )・A/ΔT・α …(2) where A: Drainage pond cross-sectional area [m ² ] H _nax : Maximum value of drainage pond water level [m] H _lpw : Drainage pond water level lower limit setting Value [m] ΔT: Filter cleaning cycle [h] α: Control parameter Q _r : Target value of wastewater return flow rate [m ³ /h].

Next, in step 106, the wastewater return flow rate target value Q _r is output to the flow rate control device 7 online.
Here, the flow rate control device 7 controls the return pump 9 and the flow rate adjustment valve 10 so that the target value Q _r of the waste water return flow rate added thereto is equal to the waste water return flow rate Q _b detected by the flow meter 11 . Control. Further, in step 106, a time wait is performed until the time set in a timer (not shown) has elapsed. This time is set to approximately ΔT/10 with respect to the cleaning cycle ΔT.

Figure 3 shows the cleaning drainage flow rate in this flow rate control.
This figure shows the temporal relationship between the wastewater return flow rate and the water level of the drainage basin. When multiple filter basins are sequentially washed at a period of ΔT, it is assumed that the washing wastewater flow rate changes by ΔQ, as shown in figure a. The maximum value of the water level in the drainage basin also changes according to this flow rate difference ΔQ, but this deviation is absorbed in one cleaning cycle ΔT, and as a result, the wastewater return flow rate Q _b remains constant as shown in Figure b. It is maintained. At this time, the water level h of the drainage pond 8 is c
As shown in , it changes toward the lower limit set value H _lpw during the ΔT time.

Thus, according to this embodiment, even if there is some variation in the flow rate of cleaning wastewater from filter to filter, the target value of the wastewater return flow rate is determined according to equation (2), so these variations can be eliminated by changing the cleaning cycle. Since it is absorbed at ΔT, fluctuations in the wastewater return flow rate Q _b can be suppressed to a significantly low level, thereby preventing deterioration in the quality of purified water.

By the way, as shown in Figure 3c, the water level of the drainage pond is H nax (1)>H between the maximum value H _nax (1) at time t ₁ and the maximum value H _{nax (0)} at time t ₂ . When there is a relationship of _nax(0) , if the target value of the wastewater return flow rate is determined by taking into account its change tendency, the variation in the wastewater return flow rate Q _b can be further suppressed.

FIG. 4 shows another embodiment in which such control is carried out, and in the figure, the same reference numerals as in FIG. 1 indicate the same elements. The first point is that the control device 20b includes the parameter calculation means 23.
It is different from the illustration.

Here, the parameter calculation means 23 determines the control parameter α shown in equation (2), and can be calculated as follows.

Generalizing the above formula (2), the return flow rate target value Q _r (n) considering the influence up to the maximum value n times before is calculated as Q _r (n) = (H _nax(0) −H _lpw )・A /ΔT・α ₀ + (H _nax(1) −H _lpw )・A/ΔT・α ₁ +…………………… +(H _nax(o) −H _lpw )・A/ΔT・α _o ...(3) It is expressed as.

However, H _nax(0) : Current maximum value H _nax(1) : Previous maximum value H _nax(o) : Local maximum value n times ago α ₀ , α ₁ , ..., αn : Control constant be.

Here, as an example, in order to obtain the control parameter α in the case of n=1, when the above equations (2) and (3) are equal, the following equation holds true.

(H _nax(0) −H _lpw )・A/ΔT・α = (H _nax(0) −H _lpw )・A/ΔT・α ₀ + (H _nax(1) −H _lpw )・A/ΔT・α ₁ = (H _nax(0) −H _lpw )・A/ΔT・(α ₀ +H _nax(1) −H _lpw /H _nax(0) −H _lpw・α ₁ )…(4) ∴α＝α ₀ +H _nax(1) −H _lpw /H _nax(0) −H _lpw・α ₁ …(5) The first term on the right side of equation (5) is the constant term of the control parameter, and the second term is the previous term. This term takes into consideration the change tendency of the current maximum value with respect to the maximum value.

Thus, the control parameter α is given by the following equation.

α=f(α ₀ , α ₁ , ..., α _o , H _nax(0) , ..., H _nax(o) , H _lpw ...(6) When the control parameters are determined as above, the flow rate target value The calculating means 24 calculates the wastewater return flow rate target value Q _r using the control parameter α in the above equation (2) as a variable as well.

Thus, according to the embodiment shown in FIG.
Since Q _r is changed, the variation in the wastewater return flow rate Q _b can be further suppressed compared to the embodiment shown in FIG.

By the way, in order to prevent the drainage pond 8 from overflowing, the cleaning control device 13 (see Fig. 1) of the water purification plant is designed to prohibit cleaning when the drainage pond water level h exceeds the upper limit setting value. Interlocked. This cleaning control device 13 is combined with the wastewater return flow rate control device to adjust the control parameter α in equation (2) above, and by setting ΔT as the basic cycle of cleaning, variations in the flow rate of filter cleaning drainage water can be reduced. If this is absorbed by delaying the cleaning cycle, the fluctuation in the waste water return flow rate can be further reduced.

That is, by setting the drainage pond water level upper limit set value H _high to an appropriate value, H _high and α are set so that the cycle ΔT is shorter than the time when the wash prohibition interlock is released. As a result, the cleaning control device 13 waits for cleaning after ΔT time from the end of one cleaning, and the water level h of the drainage pond becomes h=H _high
Start cleaning at the same time. Therefore, when the flow rate of cleaning wastewater is large, the cleaning cycle becomes long, and conversely, when the flow rate is low, the cleaning cycle becomes short.

Thus, the fluctuation in the wastewater return flow rate is smaller than in the above two embodiments.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to operate the wastewater return operation with the least fluctuation in filter wash water, and the amount of water supplied to the receiving well, which has a significant impact on the water quality treatment process, is stabilized. This makes it possible to improve the quality of purified water at water treatment plants.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of an embodiment of the present invention together with the process of a water purification plant, and Fig. 2 is a flowchart for explaining the operation of the embodiment.
Figures 3a, b, and c are time charts for explaining the operation, Figure 4 is a block diagram showing the configuration of another embodiment of the present invention together with the water treatment plant process, and Figure 5. is a diagram showing the general process of a water treatment plant. 2...Water landing well, 4...Filtration basin, 7...Flow rate control device, 8...Drainage pond, 20a, 20b...Control device, 21...Water level tracking means, 22...Extreme value detection means, 23... . . . parameter calculation means, 24 . . . flow rate target value calculation means, 25 . . . condition setting means.

Claims (1)

[Scope of Claims] 1. In a wastewater return flow rate control device for a water purification plant that controls the flow rate of washing wastewater from a filtration basin and returned to a receiving well via a drainage basin, the detected water level of the drainage basin is measured in time. water level tracking means to be stored in correspondence; extreme value detection means for detecting an extreme value of the water level of the drainage basin based on the water level data of the water level tracking means; and a cleaning cycle of the filtration basin and an allowable limit of the water level of the drainage basin. and a flow rate target value calculating means for calculating a wastewater return flow rate target value based on the set value of the condition setting means and the extreme value detected by the extreme value detecting means, A wastewater return flow rate control device for a water purification plant, characterized in that the wastewater return flow rate is controlled in accordance with a wastewater return target value. 2. A water level at which the detected water level of the drainage pond is stored in correspondence with time in a wastewater return flow rate control device of a water purification plant that controls the flow rate of wastewater return for returning cleaning wastewater from a filtration basin to a receiving well via a drainage basin. A tracking means, an extreme value detection means for detecting an extreme value of the drainage pond water level based on the water level data of the water level tracking means, and a control parameter is calculated based on a temporal change rate of the extreme value detected by the extreme value detection means. parameter calculation means for
a condition setting means for setting the cleaning cycle of the filtration basin and an allowable limit of the water level of the drainage basin; and a condition setting means based on the set value of the condition setting means, the detected extreme value of the extreme value detection means, and the control parameter of the parameter calculation means. A wastewater return flow rate control device for a water purification plant, comprising a flow rate target value calculating means for calculating a wastewater return flow rate target value based on the calculated wastewater return flow rate target value, and controlling the wastewater return flow rate in accordance with the calculated wastewater return flow rate target value. .