JPS62237994A - Apparatus for controlling injection of chlorine - Google Patents

Abstract

PURPOSE:To control the injection of chlorine in proper quantities, by calculating a chlorine injection ratio Sn by a first operation means and subsequently calculating a chlorine injection ratio Sn' injected actually by a second operation means. CONSTITUTION:Raw water and return waste water are introduced into a water arrival well 1 respectively separately and mixed to be made to flow down to a mixing basin through a flowmeter 2. Not only chlorine but also a flocculant or a neutralizing agent are injected in water on the way of the flowing-down from the water arrival well to the mixing well to be mixed in the mixing basin 3. A first operation means 7 uses feedback correction quantity to calculate a chlorine injection ratio objective value Sn synchronous to control and a second operation means 9 uses a flow amount, a measured flow amount, the concn. of the residual chlorine of the mixing basin and a chlorine injection ratio objective value Sn as input values to correct the chlorine injection ratio objective value Sn to calculate Sn'. By this method, drinking water having sanitary and stable quality is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a chlorine injection control device for a water purification plant that returns wastewater containing residual chlorine, mixes it with raw water, and reuses it.

(Conventional technology) Chlorine injection control in water treatment plants is important for oxidizing and disinfecting raw water, as well as protecting sedimentation basins and filtration basins that are part of the water treatment process, and controlling the quality of treated water due to excessive chlorine injection. and prevent the decline of

This is an important operation to save on chemical costs.

Pre-chlorine injection control causes changes in the chlorine demand of raw water, decomposition of residual chlorine due to solar radiation, and scattering of residual chlorine due to wind. In addition, when cleaning wastewater from a filtration basin containing residual chlorine is returned and used for rIi together with raw water, the chlorine contained in the returned wastewater and chlorine-consuming substances in the raw water react before reaching the chlorine injection point. Therefore, the amount of chlorine required in the treated water at the chlorine injection point changes as the ratio of wastewater return water to treated water changes. For this reason, returning the wastewater caused a control disturbance, making the quality of the treated water unstable.

Conventionally, for such disturbance elements, the chlorine demand of the treated water is calculated from the difference between the chlorine injection rate after chlorine injection and the residual chlorine concentration measured downstream of the chlorine injection point, and the residual chlorine is A method was used in which the chlorine injection rate was determined by adding the set target value for the chlorine concentration.

In addition, the chlorine consumption rate is calculated from the ratio of the executed chlorine injection rate and the measured value of the residual chlorine concentration, and the value obtained by dividing the target value of the residual chlorine concentration by this chlorine consumption rate is set as the standard injection rate. There has been a method of setting the chlorine injection rate to be executed as a value obtained by adding a feedback injection rate based on PID calculation using the residual chlorine concentration to the residual chlorine concentration.

(Problem to be solved by the invention) The former method above is basically feedforward control, but the measured values of the chlorine injection rate and residual chlorine concentration at different times are used to calculate the chlorine demand of the treated water. Because it is used,
Based on these differences, the amount of chlorine required for treated water cannot be calculated correctly. The latter method improves the deficiencies of the former by using the measured values of the chlorine injection rate and residual chlorine concentration at the same time to calculate the chlorine consumption rate. However, in the latter method, even if there is no disturbance in the chlorine demand of the treated water, if the chlorine injection rate is too high, the residual chlorine concentration will increase, so the chlorine consumption rate calculated as described above will increase. will decrease. On the other hand, if the chlorine injection rate is too low, the residual chlorine concentration will be low, resulting in a high chlorine consumption rate. For this reason, the latter chlorine injection control does not correctly compensate for the disturbance, which is the objective of the control, which is the fluctuation in the amount of chlorine required for the treated water. Furthermore, since the latter method basically uses feedback control based on PID calculation, there is also the time required for the flow from the chlorine injection point to the point where the sample water is taken, and the amount of time required to guide the sample water to the residual chlorine concentration meter. Since the time required for this is considerably longer than that for control synchronization, there is also the problem that a delay in control response occurs in response to large fluctuations in the flow rate of returned wastewater.

Therefore, the control of the chlorine injection rate determined according to the method described above was not accurate enough. The purpose of the present invention is to control the chlorine injection rate when the wastewater return water containing residual chlorine is mixed with the raw water. Even if the flow rate of wastewater returned increases or decreases, and the ratio of returned wastewater to the treated water changes,
It is an object of the present invention to provide a chlorine injection control device that prevents excessive or insufficient chlorine injection in response to this disturbance.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides chlorine that is controlled to obtain a predetermined residual chlorine concentration by injecting chlorine into treated water that is a mixture of raw water and wastewater return water containing residual chlorine. This relates to an injection control device, and first, a first calculation means calculates chlorine based on the difference between the residual chlorine concentration of the water to be treated measured by a residual chlorine meter installed downstream of the chlorine injection point and a preset residual chlorine concentration target value. Injection rate Sn
seek.

Next, based on the chlorine injection rate Sn determined by the first calculation means, the second calculation means determines the change in the ratio of the wastewater return water to the flow rate of the water to be treated and the substances that consume chlorine in the raw water. The actual chlorine injection rate S that should be corrected using the concentration of S. ′.

(Function) In the present invention, the second calculation means performs a correction calculation when the amount of returned waste water changes with respect to the chlorine injection rate obtained by the first calculation means when the amount of returned waste water does not change. ,
Disturbances such as changes in wastewater return water can be controlled without over- or under-injection of chlorine.

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

In FIG. 1, raw water taken from a water intake source (not shown) and wastewater return water are each separately led to a landing well 1, mixed in the landing well 1, and then flowed down to a mixing pond 3 via a flow meter 2.

On the way from this landing well to the mixing pond 3, chlorine is injected, and a flocculometer, neutralizing agent, etc. are injected from corresponding injection machines (not shown) and mixed in the mixing pond 3. .

The water to be treated that has flowed out of the mixing pond 3 further flows down to the floc formation pond 4. A portion of the water to be treated is taken by a water test pump 5 near the outlet 10 of the mixing pond 3, and is led to a residual chlorine meter (hereinafter referred to as a residual salt meter) 6 that measures the residual chlorine concentration.

7 is a first calculation means which inputs the signal R8 of the residual salt meter 6, and uses the control target set value Sv of the residual chlorine concentration set by the setting device 8 to calculate the feedback correction amount ΔS of the chlorine injection rate according to the following formula. Calculate.

E N = S V Re
”'(1)△5=Kp(EN EN')+Ki・EN
...■Here, EN is the input deviation of the current control cycle, EN'
is the input deviation of the previous control cycle, KP is the proportional gain, and K.

is the integral gain.

The first calculation means 7 uses the feedback correction amount ΔS obtained as described above to calculate the target value Sn of the chlorine injection rate for the current control cycle according to the following equation.

5n=Sn-, +△S...■Here S
n-1 is the chlorine injection rate target value of the previous control cycle.

The second calculation means 9 calculates the flow rate q measured by the wastewater return water flow meter 10, the measured flow rate Q of the flow meter 2 provided at the inlet of the mixing basin 3, and the residual chlorine at the outlet of the mixing basin 3 by the residual salt meter 6. The concentration R0, the parameters set by the setting device 11, and the chlorine injection rate target value S which is the output value from the first calculation means 7. As input value, chlorine injection rate target value Sn
is modified by the following equation.

Sn'=So+K...(c) Here S. ' is a corrected chlorine injection rate target value, which is a corrected injection rate based on the wastewater return flow rate, which takes a different value depending on the condition P described later, as shown in the following equation.

Here, qn is the wastewater return flow rate for the current control cycle.

'In-5 is the waste water return flow rate in the previous control cycle, and is a parameter. Further, Cd is the concentration of a substance that consumes chlorine contained in raw water.

Further, condition P is that all of the following three items are satisfied.

1/- ■->k2.

■(qn>qn and R6≧Rch) is not true.

(2) (qn-t<qn and Rc≦Rnj).

However, k2. Roh, Ro, is a parameter.

Here, if the above conditions do not hold, the amount of returned wastewater 'Tn is sufficiently small, so there is no influence from the residual chlorine and there is no need to make corrections. In addition, if condition ① does not hold, the residual chlorine concentration R9 in the water to be treated is too high.
Control is carried out to reduce this, but since the amount of wastewater returned this time has decreased, the residual chlorine concentration will continue to decrease. When correction is performed, the degree of decrease becomes smaller.

Therefore, no correction is made. If condition ■ does not hold, it is the opposite of condition ■, and the residual chlorine concentration R8 of the water to be treated is too low.
Controls will be implemented to increase this, but since the amount of returned wastewater qn has increased, the residual chlorine concentration will continue to rise. If correction is performed, the degree of increase will be reduced. Therefore, no correction is made.

Note that the parameters are 1. k2. Rch, RcJ are
This is a plant-specific constant that is determined by analyzing plant operating data. It should be noted that the second calculation means 9 is provided with a setting device 11 that can manually set the above-mentioned parameters, and it is also possible to modify the values based on the operator's judgment.

The second calculation means 9 determines the target value Sn' of the chlorine injection rate.
The process of calculating is shown in Figure 2.

Figure 3 shows the effect when the wastewater return flow rate changes. In the case of the conventional method, when the wastewater return flow rate changes, the residual chlorine concentration in the mixing pond also changes, resulting in unstable water quality. In the method according to the present invention, the residual chlorine concentration in the mixing pond does not change suddenly, and chlorine injection is well controlled.

〔Effect of the invention〕

As explained above, if chlorine is injected using the chlorine 2+ input control device of the present invention, it becomes possible to automatically inject chlorine even when the return flow rate of wastewater containing residual chlorine changes, which was difficult to deal with with conventional methods. , it is possible to supply drinking water of hygienic and stable quality.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the chlorine injection control device according to the present invention, Fig. 2 is a flowchart showing the calculation flow of the control device in an embodiment of the present invention, and Fig. 3 shows the effects of the present invention. It is a characteristic diagram shown in comparison with the conventional one. 1... Water landing well 2... Flow meter 3... Mixing pond 5... Water test pump 6... Residual salt meter
7... First calculating means 8... Setting device 9
... Second calculation means 10 ... Drainage return flowmeter 11
...Setting device agent Patent attorney Nori Chika Ken Yudo Hirofumi Mitsumata Figure 2 Sakima (Tokoban; Law) Unexamined Patent Publication Figure 3

Claims (1)

[Scope of Claim] A chlorine injection control device that injects chlorine into treated water that is a mixture of raw water and wastewater return water containing residual chlorine, and performs control to obtain a predetermined residual chlorine concentration, comprising: a first calculating means for calculating a chlorine injection rate S_n based on the deviation between the residual chlorine concentration of the water to be treated measured by the residual chlorine meter installed downstream of the point and a preset residual chlorine concentration target value; Based on the chlorine injection rate S_n obtained by the method, correction is made using the change in the ratio of the wastewater return water to the flow rate of the water to be treated and the concentration of the substance that consumes chlorine in the raw water, and the actual injection rate is determined. A chlorine injection control device comprising: second calculation means for determining a chlorine injection rate S_n'.