JPH0790226B2 - Pre-chlorination control system for water treatment plant - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a pre-chlorine injection control device for a water treatment plant, which copes with decomposition of residual chlorine due to solar radiation.

(Prior Art) FIG. 4 shows a conventional chlorine injection control device for a water treatment plant. In FIG. 4, raw water flows into the landing well 1, and chlorine for disinfection and an alkaline agent for pH adjustment from an alkali injection device (not shown) are injected at this outlet. Further, the treated water is injected with a coagulant from a coagulant injection device (not shown) for turbidity, and is rapidly stirred by the flash mixer 3 in the rapid mixing basin 2. Flock is formed in the floc formation pond 4 and most of the flocs are precipitated and removed in the settling pond 5.

Raw water contains microorganisms including inorganic substances, organic substances and pathogens, and injected chlorine loses its oxidizing ability by reacting with these substances and microorganisms. Also settling tank 5
Generally has a long residence time, and while the treated water passes through the settling basin 5, residual chlorine in the treated water is decomposed by irradiation of sunlight or partly scattered. This effect is particularly noticeable in the summer when the amount of solar radiation is large.

The water that has passed through the settling tank 5 is clarified in the filter tank 6, and post-chlorine is injected by a post-chlorine injector (not shown) and stored in the purification tank 7.

Conventionally, chlorine injection control is performed by the PID calculator 24 based on the indicated value of the residual chlorine concentration meter 8 installed at the entrance of the floc formation pond 4.
Feedback control is performed by the
The residual chlorine concentration of the outlet water was measured and feedback control was performed according to the indicated value.

As still another conventional technique, a method of converting the measured insolation into an injection rate by a linear expression and correcting the injection rate, or increasing the measured insolation in the morning ahead of time and converting this into an injection rate There was a way to make a correction.

However, in these conventional methods, when water intake is intermittent, feedback control becomes unstable, and even when water intake is stopped, the calculation of feedforward control proceeds and the amount of chlorine decomposition due to solar radiation cannot be corrected. As a result, the residual chlorine concentration at the outlet of the sedimentation tank could not be maintained at the target value.

On the other hand, when chlorine injection is performed by manual operation instead of the above-mentioned automatic operation, the sedimentation tank 5 should be checked while observing the weather of the day.
The operation was to increase the chlorine injection rate at an early stage by taking into consideration the flow-down time until and to decrease the chlorine injection rate from early afternoon to early evening. This method has a drawback in that the residual chlorine concentration is excessive or deficient because the injection rate is changed stepwise rather than changing the injection rate in accordance with the change in the amount of solar radiation which is a control disturbance.

(Problems to be solved by the invention) That is, the problem to be solved by the invention is that the injection rate of pre-chlorine is adjusted so as to compensate the decomposition of chlorine in the settling tank due to solar radiation on the next day even if the water intake at night is interrupted. Is a feedforward correction.

Therefore, an object of the present invention is to compensate for the amount of chlorine lost in the settling tank due to solar radiation, and to maintain the residual chlorine concentration at the outlet of the settling tank at a target value even if the water intake is interrupted. To provide.

[Structure of Invention]

(Means for Solving Problems) In the pre-chlorination control device for the water treatment plant according to the present invention, the first calculation is performed to determine the water level of the water purification pond and the amount of water supplied from the water purification plant to the customer, particularly at night. Find the stop time t _S.

A time t _h obtained by summing a predetermined time h and the water intake suspension time obtained by the first calculation means from each of the preset times from sunrise to sunset by the second calculation means.
Calculate the predicted solar radiation amount R _Et for each time before = h + t _s .

The third calculation means uses the predicted solar radiation amount R _Et-h at the current time and the actual solar radiation amount measured value R _PV obtained at the current time, and the predicted solar radiation amount R obtained at that time.
_The solar radiation amount correction value R _t with _Et corrected is _calculated , and the solar radiation amount correction value is calculated.
Based on R _t , the amount of residual chlorine decomposed by solar radiation by the fourth calculation means
Calculate DS _t .

The fifth calculation means obtains the chlorine injection rate CL _t from the deviation between the actual measurement value of the residual chlorine concentration in water and the target residual chlorine concentration using the above-mentioned residual chlorine decomposition amount DS _t as a correction value.

The sixth calculating means obtains the manipulated variable correction value DV _t for the response delay from the tendency of the change in the solar radiation correction value R _{t up to} the present time.

Then, the chlorine injection rate CL _t and the manipulated variable correction value DV _t are added by the adding means to obtain the chlorine injection amount set value.

(Operation) In the present invention, in particular, the water intake suspension time at night is predicted, the transition of the solar radiation amount of one day is predicted in consideration of this suspension time, the decomposition amount of chlorine due to this solar irradiation is grasped, and this decomposition is calculated. Since the control is performed so that the residual chlorine concentration in water matches the target value by using the amount as a correction value, it is possible to always obtain the required residual chlorine concentration.

(Embodiment) An embodiment of the present invention will be described with reference to FIG.

The same parts as those in FIG. 4 are designated by the same reference numerals.

Chlorine and an alkali agent from an alkali injection device (not shown) are injected into the raw water at the outlet of the landing well 1. Further, the coagulant is injected from the coagulant injection control device (not shown) at the inlet of the rapid mixing basin 2, and is rapidly stirred by the flash mixer 3 in the rapid mixing basin 2. In the floc formation pond 4, flocs grow, and in the settling pool 5, most of the grown flocs are removed by precipitation. The outflow water from the settling basin 5 is clarified in the filtration basin 6, and post-chlorine is injected by a post-chlorine injecting machine (not shown) to be stored in the water purification basin 7. Flock formation pond 4
The inlet water and the outlet water of the settling basin 5 are introduced into the residual chlorine concentration meter 10 and the residual chlorine concentration meter 11 by the inspection water pump 8 and the inspection water pump 9, respectively. The indicated values of the respective residual chlorine concentration meters 10 and 11 are monitored by the operator.

In FIG. 1, the first calculating means 12 is a signal (water level) LR of the water level meter 13 of the water purification reservoir 7 and a signal of a tap water flow meter 14 sent from the water purification reservoir 7 to a consumer by a water pump (not shown) ( water supply amount) Q _e for the predicted value Q _E from nighttime intake stop time t _S
Is calculated. This intake stop time t _S is the predicted value Q _E
And the water level in the water purification pond 7 is the amount of tap water used the next morning, that is, the water level set value that is the predetermined outflow before the increase in the amount of water sent, LS, L
It is obtained from H and the condition of the following equation.

Here, LR: Water level at the current time LH: Water level upper limit value LS: Target value Water level set value S: Purification area Q _I : Treatment amount Q _E : Predicted amount of water supply t _S : Stoppage time of water intake The value Q _E can be easily obtained by data analysis using a general statistical method based on the measured value Q _e .

The second calculating means 15 has an early sunrise time h before the actual insolation starts and the water intake stop time t _S obtained by the first calculating means.
The predicted insolation amount is calculated from the sum of and t _h = h + t _S. This predicted solar radiation amount R _Et is the bearing p of the water treatment plant,
It is a function of the calendar m and the current time t.

R _Et = f (p, m, t) (2) Specifically, the sunrise and sunset times were calculated using the data of the science chronology (1984, Tokyo Observatory edition), and both The sunshine duration T _S calculated from the time and the maximum solar radiation amount R _max of one day represented by a sine wave function having a cycle of one year are calculated by the formula (3).

R _max is calculated by the equation (4).

However, α, β, and γ are coefficients that can be obtained from sunshine data for the past several years. d'is the number of days from New Year's Day until the day when control is performed.

The third calculation means 16 is an output obtained by the second calculation means 15 before time t. Current predicted solar radiation amount R _Et-h
And the indicated value R _PV of the insolation meter 17 are compared, and the corrected value R _t of the insolation amount is calculated according to the equation (5).

_{R t = R Et + k 1} · (R PV -R Et-h) ... (5) provided that k ₁ is a constant, having a value specific to water treatment plants.

The fourth calculating means 18 calculates the residual chlorine decomposition amount DS _{t due} to the amount of solar radiation according to the equation (6) based on the corrected amount of solar radiation R _t which is the output of the third calculating means 16.

DS _t = DS _t-1 + k ₂ · k ₃ (R _t −R _t-1 ) (6) where k ₂ is a coefficient for converting the amount of solar radiation into residual chlorine concentration, and k ₃ is a constant. R _t-1 is the corrected solar radiation value of the previous calculation cycle.

In the fifth calculating means 19, the residual chlorine decomposition amount DS _t by the amount of solar radiation obtained by the fourth calculating means 18 and the actually measured residual chlorine concentration R
Input _C and _C and feed back chlorine injection rate CL _t
To calculate. However, the deviation E _t used here is not only the difference between the preset residual chlorine target value R _SV and the actually measured residual chlorine concentration R _C , but also the residual chlorine decomposition amount as shown in equation (7). It is also modified by DS _t .

The _{E t = R SV -R C +} DS t ... (7) chlorine injection rate CL _t using the deviation E _t first (8), (9)
Calculate by formula.

CL _t = CL _t-1 + △ CL (8) △ CL = k _C {k _p · (E _t −E _t-1 ) + k _j · E _t … (9) where k _C , k _p , k _j is the control gain.

Further, even if chlorine is injected at the chlorine injection rate obtained by the fifth calculating means 19, there is a response delay until the effect appears. Therefore, in order to perform quick control, a correction calculation for this feedback output value is performed. The calculation means 20 is used. The corrected value DV _t of this manipulated variable is based on the corrected amount of solar radiation R _t which is the output of the third computing means 16, and the following (1
It is calculated by equation (0) and equation (11).

DV _t = DV _t-1 + DM _t (10) DM _t = DM _t-1 + k ₂ · k ₄ · (R _t −2R _t-1 + R _t-2 ) (11) where k ₄ is a constant .

The adding means 21 adds the chlorine injection rate CL _t by feedback which is the output value of the calculating means 19 in FIG. 5 and the manipulated variable correction value DV _t which is the output value of the sixth calculating means to obtain a chlorine injection rate set value. Is calculated. This chlorine injection rate set value is transmitted to the controller 22 which controls the chlorine injection amount, where it is converted to the chlorine injection amount set value by multiplying by the rapid mixing tank inflow amount, and the chlorine injection amount is controlled. .

Figure 2 shows the actual amount of radiation from sunrise to sunset in the above control.
FIG. 3 shows the relationship in the present invention of RPV, residual chlorine concentration DS _t decomposed by solar radiation, and predicted solar radiation amount R _Et .

FIG. 3 is a graph showing the effect in the above-described embodiment of the present invention, where A is the actual amount of solar radiation, and B and C are the residual chlorine concentration in the inlet water and the residual chlorine concentration in the precipitation water of the floc formation pond 4, respectively. 3 is a graph comparing the results according to the invention with the results according to the prior art. In this way, in particular, taking into account the stoppage of water intake at night, the response delay is compensated for the disturbance due to solar radiation by the predicted amount of solar radiation in a feedforward manner, and the excess amount is corrected by the measured amount of solar radiation, and chlorine injection is performed. As a result, the residual chlorine concentration at the outlet of the settling basin can be adjusted to the target value, and the quality of the treated water can be stabilized. In addition, it is possible to prevent the generation of algae due to sludge decay in the sedimentation basin caused by the decrease in residual chlorine, and to supply sanitary and safe water.

〔The invention's effect〕

As described above, according to the present invention, sometimes the amount of chlorine divided by solar radiation is grasped in consideration of the water intake stop time at night, and chlorine injection is controlled, so that the required residual chlorine concentration is always maintained, Good processing can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a pre-chlorine injection control device for a water treatment plant according to the present invention, FIG. 2 is an explanatory view of the operation of the present invention, and FIG. 3 shows effects of the embodiment according to the present invention. FIG. 4 is a block diagram showing a conventional device. 1 ... Landing well, 2 ... Rapid mixing pond, 4 ... Flock formation pond, 5 ... Sedimentation pond, 6 ... Filtration pond, 7 ... Purification pond, 8, 9 ... Test pump, 10, 11 ... Residual Chlorine concentration meter 12 …… first calculation means, 13 …… water level meter 14 …… flowmeter, 15,16,18,19,20 …… calculation means 17 …… solar radiation meter, 21 …… addition means 22… … Controller, 23 …… Flowmeter

Claims (1)

[Claims] 1. A pre-chlorination control device for a water treatment plant for controlling the amount of chlorine injection into raw water, wherein a first intake stop period at night is determined based on the water level of the water purification pond and the amount of water sent from the water purification pond. From the calculation means and before the time of the sum of the water intake stop time and the predetermined time h,
The calculation is stopped during the time period when the water intake is stopped, and the second calculation means for obtaining the predicted solar radiation amount R _Et for each hour and the prediction of the current time obtained by the second calculation means Third calculation means for obtaining a solar radiation amount correction value R _t by correcting the predicted solar radiation amount R _Et obtained at that time using the solar radiation amount R _Et-h and the solar radiation amount actually measured value R _{PV at} that time; Based on the amount correction value R _t , residual chlorine decomposition amount due to solar radiation DS
_A fourth calculation means for obtaining _t, and a fifth calculation means for obtaining the chlorine injection rate CL _t from the deviation between the actual measurement value of the residual chlorine concentration in water and the target residual chlorine concentration using the above-mentioned residual chlorine decomposition amount DS _t as a correction value. And a sixth calculation means for obtaining the manipulated variable correction value DV _t for the response delay from the tendency of the change of the solar radiation correction value R _{t at} the present time, and the chlorine injection rate CL _t and the manipulated variable correction value DV _t . In addition, a pre-chlorination control device for a water treatment plant equipped with an addition means for obtaining a chlorine injection amount set value.