JPS6111192A - Chlorination control device for filtration plant - Google Patents

Abstract

PURPOSE:To stabilize the concn. of residual chlorine by providing the 1st calculator which calculates the feedback correction quantity of chlorine dosage from the measured value of the concn. of the residual chlorine at a required point and the target value thereof and the 2nd calculator which calculates the presumed value. CONSTITUTION:The original water flows through a pipeline A into a water bed 2 and flows through a pipeline B where chlorine is added into a quick mixing basin 3. The treated water in the basin 3 is sampled by a water check pump 4 and is fed through a conduit D into a residual chlorine concn. meter 6 by which the concn. RC is measured. The measured concn. value RC, the original water flow rate Q measured by a flowmeter 1 provided to the pipeline A and chlorine water flow rate QC are inputted to an arithmetic device 8 for chlorination by which the adequate chlorine dosage MV is calculated. The flow rate QC is controlled by a chlorination controller 17 and a chemical feed valve 6 so as to meet the MV.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention adjusts the amount of chlorine injection in a water treatment plant so that the residual chlorine concentration remains constant by taking into account the temporal and spatial lag between the chlorine injection point and the residual chlorine concentration measurement point. This article relates to a chlorine injection control device for a water purification plant that controls the chlorine injection so that the following occurs.

[Technical background of the invention and its problems]

Chlorine injection at water treatment plants includes pre-chlorine injection into the raw water, medium chlorine injection before the filtration basin, and post-chlorine injection after the filtration basin. Because it takes a long time for the flow to reach this point, stable control is difficult with normal feedback control.

For this reason, conventionally, (a) Calculate the chlorine demand of raw water by comparing the executed chlorine injection rate and the measured value of residual chlorine concentration, and calculate the chlorine injection rate by adding the target value of residual chlorine concentration to this. (b) Calculate the chlorine consumption rate from the ratio of the executed chlorine injection rate and the measured value of the residual chlorine concentration, and set the value where this chlorine consumption rate meets the target value of the residual chlorine concentration as the standard injection rate, In addition to this standard injection rate, PID uses the measured value of residual chlorine concentration.
A method is used in which the value obtained by adding the calculated feedback injection rate is used as the chlorine injection rate to be executed.

However, although method (a) above is basically feedforward control, it uses the chlorine injection rate and residual chlorine concentration at different times to calculate the chlorine demand of raw water, so the calculation cannot be performed correctly. ．． In addition, method (b) above uses values for the chlorine injection rate and residual chlorine concentration at the same time, so there is no problem like method (a), but the chlorine demand of the raw water, which is a disturbance, does not fluctuate. However, if the chlorine injection rate is high, the residual chlorine concentration will also be high, and if the chlorine consumption rate is low, the residual chlorine concentration will be low and the chlorine consumption rate will be high. Therefore, it is difficult to properly compensate for disturbances such as fluctuations in chlorine demand. Furthermore, even though the measurement time is the same, the chlorine injection rate and residual chlorine concentration are measured at different positions, and are affected by the mixing characteristics of the process between the chlorine injection point and the residual chlorine concentration measurement point, so the calculated value of the chlorine consumption rate does not show the correct value, resulting in inaccurate control of the chlorine injection rate.

[Purpose of the invention]

The present invention calculates the relationship between the chlorine injection rate and the residual chlorine concentration by correcting the deviation of the measurement time and measurement position using a mixing model of the injection chlorine and raw water, and uses this as a PID feedback control system. The object of the present invention is to provide a chlorine injection control device for a water treatment plant that appropriately controls the chlorine injection rate.

SUMMARY OF THE INVENTION The present invention provides a chlorine injection control device for a water treatment plant that controls the amount of chlorine injected to control the residual chlorine concentration at a specified point to a target value. A first computing unit that calculates the feedback correction amount of the chlorine injection rate from the value, and a mixing model of the injected chlorine and raw water to calculate the mixed chlorine injection rate at a certain point when the injected chlorine is mixed without decomposition and loss. A second calculator that calculates the expected value, a third calculator that calculates the time change in the chlorine consumption rate from the expected mixed chlorine injection rate and the measured residual chlorine concentration, and corrects the time change in the chlorine consumption rate from the raw water flow rate. a fourth calculator that calculates the control ratio to be injected into the raw water from the feedback correction amount, time change in chlorine consumption rate, and control ratio; The chlorine water injection current is controlled accordingly, thereby compensating for the temporal and spatial deviation between the chlorine injection point and the residual chlorine concentration measurement point, making it possible to stably control the residual chlorine concentration at the required point. This is how it was done.

[Embodiments of the invention] An embodiment of the present invention is shown in FIG.

In FIG. 1, raw water taken from a water intake source (not shown) flows into the receiving well 2 through pipe A, flows into the rapid mixing basin 3 through pipe B where chlorine is injected, and then flows into the rapid mixing basin 3 through pipe B where chlorine is injected. The water is mixed with a stirrer (not shown) and flows into the next step as treated water through pipe C.

The treated water in the rapid mixing pond 3 is sampled by a water test pump 4, and the sample is sent to a residual chlorine concentration meter 6 through a water conduit, where the residual chlorine concentration RC is measured.

The raw water flow rate Q measured by the flow meter 1 installed in the residual chlorine concentration measurement value ⇠C1 and the chlorine water flow rate QC measured by the chemical flow meter 7 installed in the chlorine injection pipe E are calculated by chlorine injection calculation. The chlorine injection rate is input to the device 8, where an appropriate chlorine injection rate MY is calculated, and the chlorine water flow jiQc is controlled via the chlorine injection controller 17 and chemical injection valve 6 in accordance with MV.

Next, the calculation operation of the chlorine injection calculation device 8 will be explained with reference to the flowchart shown in FIG.

First, the above is used as process data for each calculation cycle.

RC, Q, and QC are input.

The first computing unit 10 inputs the residual chlorine concentration target value SV from the input point 9.
is set, the residual chlorine concentration measurement value RC is input, and the following equations (1) and (2) are calculated for each control cycle to calculate the feedback correction amount Δ8 of the chlorine injection rate.

gn==8v-RC-(1) h △5=Kp (In-En-x) +-VIIEn
(2) where Hn and En-x are the input deviations in the current and previous control cycles, Kp is the proportional gain, and h is the control cycle TI is the integral time.

The second computing unit 12 inputs the chlorine concentration CL of chlorine water from the input point 11.
o is set, the raw water flow rate Q and chlorine water flow rate Q'C are input, and the following equations (3) to (7) are calculated, assuming that chlorine is mixed without decomposition and disappearance. The residual chlorine concentration (hereinafter referred to as mixed chlorine injection rate) CLs at the measurement point in the case is calculated using the following formulas (3) to (7).

CLi=CLt-TB
-(3) CLe = α, CLi + (1-α),
CLm − (5) CLs = CLe(t-T
C) - (6) Here, CL is the mixed chlorine injection rate at the chlorine injection point CLi is the mixed chlorine injection rate at the point where it flows into the rapid mixing basin 3 from pipe B, and CLt-TB is the water introduction time delay in pipe B CL before TB, CLm is the mixed chlorine injection rate of the complete mixing part of the rapid mixing tank, and CLm' is the usual C
Lm, α is the ratio of raw water that short-circuits the complete mixing part (0≦α
≦l ), CLe is the mixed chlorine injection rate of the sample water pumped up by the sample water pump 4, and TC is the water conveyance delay time in the water conveyance pipe.

The third calculator 13 inputs the above CLs and RC", calculates the following equations (8) and (9), and calculates the chlorine consumption rate DC.
Calculate the time change ΔDCL of L.

DCLn = CLs - RC - (8) ΔDcL =
DCLm −DCL n−1・= (9) Here, DCL
n −1 is the previous DCLn.

The fourth computing unit 15 receives the reference ratio KCDo and the raw water flow rate Q from the input point 14, and calculates the control ratio KCD using the following equation 01.

KCD=KCDo(1+Ikujimura 3...α〔
K.

Here 1. K, , K, are constants determined by the hydraulic characteristics of the water treatment plant.

The fifth calculator 16 inputs the above-mentioned ΔS, ΔDCL, and the control ratio KCD, and calculates the chlorine injection rate MVn for the current control cycle by calculating the α·υ equation below.

MVn = Mvn-t+Δ8 + KCD-ΔDcL
Here, MVn and MVn-x are MY of the current and previous control cycles.

When the chlorine water injection flow rate QC is controlled based on the chlorine injection rate MY calculated in this way, the time delay between the chlorine water injection point and the measurement point of the residual chlorine concentration is corrected in a feedforward manner by the mixing model. Since feedback control is carried out, control followability is improved and appropriate chlorine injection control becomes possible.

Although the above embodiment deals with pre-chlorine injection, the present invention can also be applied to intermediate chlorine injection and post-chlorine injection.

〔Effect of the invention〕

As explained above, according to the present invention, the measured value of the residual chlorine concentration is compared with its target value, the chlorine injection amount is feedback-controlled according to the deviation, and the chlorine injection is performed assuming a mixed model of a water treatment plant. Since the temporal and spatial deviation between the measurement point and the residual chlorine concentration measurement point is compensated for in a feed-reward manner, control followability is improved and the residual chlorine concentration can be stably controlled relative to the target value. becomes possible.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing one embodiment of the present invention, and Fig. 2 is a system diagram showing an embodiment of the present invention.
It is a flowchart which shows the calculation operation in a figure. 1 Raw water flow meter 2 Landing well 3 Rapid mixing basin 4 Water test pump 5 Residual chlorine concentration meter 6 Chemical injection pulp 7 I chlorine water flow meter 8 Chlorine injection calculation device 10.12.13, 15.16 Calculation unit 17 Chlorine injection control vessel

Claims (1)

[Claims] In a chlorine injection control device at a water treatment plant that controls the amount of chlorine injection to control the residual chlorine concentration at a specific point to a target value, feedback correction of the chlorine injection rate is performed based on the measured value of the residual chlorine concentration at a specific point and its target value. A first computing unit that calculates the amount, and a second computing unit that uses a mixing model of the injected chlorine and raw water to calculate the expected value of the mixed chlorine injection rate at the above-mentioned points when the injected chlorine is mixed without decomposition and disappearance. a third computing unit that calculates the time change in the chlorine consumption rate from the current value of the mixed chlorine injection rate and the measured value of the residual chlorine concentration; and a third calculator that calculates the control ratio that corrects the time change in the chlorine consumption rate from the raw water flow rate. 4 computing units, and a 5th computing unit that calculates the chlorine injection rate to be injected into raw water from the feedback correction amount, time change of chlorine consumption rate, and control ratio, A chlorine injection control device for a water treatment plant characterized by controlling the injection flow rate.