JP3522650B2 - Automatic coagulant injection device for water purification - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coagulant automatic injection device for water purification, which is used in, for example, a water purification plant or tertiary treatment such as sewage treatment.

[0002]

2. Description of the Related Art As a conventional automatic coagulant injection device for water purification, a chemical injection pump for injecting a coagulant into raw water to be purified water and a suspension contained in mixed water after coagulant injection by the chemical injection pump. A streaming ammeter that measures the colloidal surface charge of a substance as a streaming current, and a streaming current value at the time of optimal injection of the flocculant into the raw water is preset as a set point of a management target, and a streaming current measurement value signal is output from the streaming ammeter. A PID controller that outputs a pump control signal for controlling the drive of the chemical injection pump so that the measured flowing current value becomes the flowing current value at the set point by inputting is known. Has been.

[0003] That is, the PID controller is based on a deviation current value between a streaming current value (set point) preset therein and a streaming current measurement value input from the streaming ammeter, and the PID controller of the chemical injection pump. By controlling the drive, feedback control is performed so that the coagulant injection amount from the chemical injection pump becomes a management target value.

[0004]

Since the conventional automatic coagulant injection device for water purification is configured as described above, the flow current value of the coagulant-mixed water is measured by the flow ammeter and the measured value signal is measured. Since the feedback control is performed so that the coagulant injection amount by the chemical injection pump becomes the management target value only by so-called flowing current by inputting it to the PID controller, there were many problems as follows. The flow current value (set point) at the time of optimal coagulant injection that is preset in the PID controller is, for example, the flow current value when the quality of the inflowing raw water is stable during fine weather, and is artificially set. Therefore, it is unclear whether the coagulant injection amount is excessive or insufficient. In other words, the characteristics of the inflowing raw water fluctuate between fine weather and rainfall or when groundwater is mixed, but the flowing current value at the set point is constant even during such fluctuations. By controlling the injection amount of the agent, it was not possible to automatically control the injection pump so that the injection amount of the coagulant was adjusted according to the change in the property of the raw inflow water. The automatic control of the coagulant injection amount by only the flowing current of the inflowing raw water could be achieved only in the place where the properties of the inflowing raw water were stable. The characteristics of raw water inflowing from rivers, especially when it rains or mixes with groundwater, fluctuates drastically.Therefore, when automatic control of the coagulant injection amount is performed in anticipation of such fluctuations, flocculation is performed for safety in water purification treatment. There is a tendency to empirically increase the amount of agent injection, which results in over-injection of the flocculant,
It causes the following harmful effects. ^{-Al +3} ions in the treated water increase, which is not preferable for human health.・ Processing cost increases due to excessive injection of coagulant.・ Excess sludge increases.・ Continuation time during filtration at the latter stage of the water purification process will be shortened.・ Increase of backwash water volume and chance of leakage of protozoa such as Cryptosporidium during backwash. -Because the flow current value is a relative value, past data can only be used as a reference, and reliability is poor in automatic control of the coagulant injection amount.

The present invention has been made in order to solve the above-mentioned problems, and even if the property of inflowing raw water fluctuates, a chemical injection pump is provided so that the coagulant injection amount is optimum according to the fluctuation. It is an object of the present invention to obtain a coagulant automatic injection device for water purification that can be automatically controlled and can improve the reliability of water purification treatment.

Further, according to the present invention, the flow current value at the time of optimum coagulant injection can be preset as a control target set point, and the set point can be automatically corrected in accordance with the change in the property of the raw inflow water. It is an object of the present invention to provide an automatic coagulant injection device for water purification, which can prevent excessive injection of the coagulant, reduce the running cost of water purification treatment, and prevent the generation of excess sludge.

[0007]

SUMMARY OF THE INVENTION The water purification flocculants automatic injection device according to the present invention includes a dosing pump for injecting a coagulant into the flow Nyuhara water conductivity to measure the conductivity of the inflow raw water before coagulant injection Rate measuring means, current measuring means for measuring the flowing current value of the coagulant-mixed water after the coagulant is injected by the chemical injection pump, and the respective measurement value signals are input from the conductivity measuring means and the current measuring means. , A pump control means for controlling the drive of the chemical injection pump so that the coagulant injection amount according to the property variation of the inflowing raw water based on the measured value signal, and the pump control means, in the steady state Inflow raw water
The conductivity σ o and the flowing current value I o are
Set point for optimal injection of coagulant into raw water
Is set according to the fluctuation of the flowing current value I o.
To correct the conductivity σ o of the set point
The correction set point Is according to
And calculated based on the input signal from the conductivity measuring means.
Then, the flow current is measured by the input signal from the current measuring means.
Dosing so that the constant value i becomes the corrected set point Is.
It controls the drive of the pump .

[0008]

The pump driving means of the automatic coagulant injection apparatus for water purification according to the present invention judges whether or not the electrical conductivity σo at the time of optimal injection of the coagulant into the inflowing raw water is σo = stable,
When σo = stable, the streaming current measured value i based on the input signal from the streaming current measuring means is compared with the streaming current value Io of the raw raw water at the time of optimal injection of the flocculant. When i ≦ Io, the flocculant for the raw raw water is compared. Is increased, and when not, the injection amount of the coagulant is reduced to control the driving of the chemical injection pump so that i becomes Is.

The pump control means of the automatic coagulant injection apparatus for water purification according to the present invention has the following formula: In =
After calculating Io * [sigma] o / [sigma] n, [Delta] I = Io-In is calculated, and then it is determined whether or not i≤Io + [Delta] I = Is. When i≤Io + [Delta] I = Is, the increase amount of the coagulant injection amount is increased. Is calculated. If not, a decrease value of the coagulant injection amount is calculated so that i becomes Is, and a turbidity control signal or a streaming current control signal based on the increase and decrease values of the coagulant injection amount is calculated. Note Output to pump.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below. Embodiment 1. 1 is a schematic block diagram showing an automatic coagulant injection device for water purification according to Embodiment 1 of the present invention. In FIG. 1, 1 is a landing well for receiving raw raw water to be purified, and 2 is a water well 1. Is a chemical injection pump for injecting a coagulant into raw water advancing toward the next rapid agitation pond 3, and the rapid agitation pond 3 receives the mixed water after the aggregating agent is injected by the chemical injection pump 2 and rapidly agitates it. To do. 4 is a floc formation pond for receiving flocculant-mixed water after stirring treatment from the rapid stirring pond 3 to form flocs, 5 is a flocculation sedimentation pond for introducing mixed water from the floc formation pond 4 for solid-liquid separation, Reference numeral 6 is a rapid filtration basin for introducing the supernatant water from the coagulation sedimentation basin 5 for rapid filtration treatment, and 7 is a distribution reservoir for introducing the treated water from the rapid filtration basin 6.

Reference numeral 10 is an electric conductivity meter (conductivity measuring means) for measuring the electric conductivity of the raw water that has flowed into the landing well 1 and before the coagulant is injected, and 11 is the coagulant-mixed water stirred in the rapid stirring basin 3. , A flow ammeter (current measuring means) for measuring the flow current value of the electric current meter, 12 inputs the measurement value signals from the electric conductivity meter 10 and the flow ammeter 11, and controls the pump based on the input signals (coagulant). Injection control) PID that outputs a signal
This PID controller 1 is a controller (pump control means).
The detailed function of 2 will be described later. Reference numeral 13 denotes a turbidimeter (turbidity measuring means) for monitoring that measures the turbidity of the separated water (supernatant water (a) or intermediate clear water (b)) that has been subjected to the coagulating sedimentation treatment in the coagulating sedimentation tank 5.

Next, the operation will be described. The raw water flowing into the landing well 1 is injected with a coagulant from the chemical injection pump 2 on the way to the rapid agitation basin 3, and the coagulant mixed water is a rapid agitation basin 3 → floc formation basin 4 → coagulation sedimentation basin 5 → By passing through the rapid filtration basin 6 in sequence, the water is purified and reaches the distribution reservoir 7.

In such a water purification process, the characteristics of the raw water flowing into the landing well 1 vary greatly between, for example, fine weather and rain, but even if such variation occurs,
It is necessary to control the coagulant injection amount by the chemical injection pump 2 to be optimum. For the control, the conductivity of the raw water that has flowed into the landing well 1 before the coagulant is injected is measured by the electric conductivity meter 10 (continuously measured for 24 hours), and the measured value signal is output to the PID controller 11. . Also, the medicinal pump 2
The coagulant is injected in, and the flowing current of the microflocked mixed water after the raw water inflow and the coagulant are sufficiently stirred and mixed in the rapid agitation basin 3 is measured by the flow ammeter 11, and the measured value signal is PID. It is output to the controller 12.

Therefore, the PID controller 12 receives the electric conductivity 10 from which the electric conductivity measured value signal before the coagulant injection and the flow ammeter 11 receives the electric current measured value signal from the mixed water after the coagulant injection. The flow current value at the time of optimal injection of the flocculant into the inflowing raw water is preset in the PID controller 12 as a set point, and the flow current measurement value input from the flow ammeter 11 is set as the set point. The drive of the chemical injection pump 2 is controlled so that the flow current value becomes.

Here, when the injection rate of the coagulant with respect to the inflowing raw water is optimal, the conductivity σ of the raw water before the coagulant injection
o and the flowing current value Io of the mixed water after coagulant injection are σoIo
= The relation that becomes constant is established. For example, since the conductivity σo and the flowing current value Io are stable in fine weather, the flowing current value Io having a constant relationship with the conductivity σo at that time is set in the PID controller 12 as a set point of the management target.

Next, the flowing current of the coagulant-mixed water will be described. In general, suspended matter in raw water contains colloidal particles such as viscosity and humic substances, and the surfaces of these colloidal particles are negatively charged and repel each other, which makes it difficult to precipitate. Therefore, by injecting a coagulant having a positive charge into the raw water, the charge is neutralized to reduce the repulsive force, and by stirring, colloid particles collide,
Although flocs are formed, the quality of aggregation greatly affects the efficiency of the subsequent precipitation / filtration treatment and the quality of treated water. The quality of aggregation depends on the ratio of the charges of the negatively charged suspended substance and the positively charged flocculant. Although this ratio cannot be measured directly, it has been confirmed to correlate with the streaming current generated when motion is applied to the colloidal particles.

Here, the flow current generated when the colloidal particles are subjected to motion will be described in more detail. When the sampling water is put into a capillary tube and pressure is applied, and the sampling water is pushed through the capillary tube, the sampling water is discharged. Slide surface is generated, and the ions on the surface of the colloid move in the flow direction of the sampling water. The current flowing by the movement of the ions is called the flowing current. This flowing current can be calculated by the equation (1). I = −Kεζ (1) where I: flowing current, K: sensor coefficient, ε: relative permittivity of water, and ζ: zeta potential. Further, the streaming potential at this time can be obtained by the equation (2). E = κPζ (2) where E: streaming potential, κ: physical coefficient, and P: pressure difference.

From the above equations (1) and (2), the streaming current I and the streaming potential E are both the slip surface potential of the electric double layer,
That is, it is understood that it is proportional to the zeta potential ζ. The zeta potential ζ represents the potential difference between − and + ions, and the colloidal suspended substance contained in the treated water is electrostatically −
It is charged with ions. On the other hand, since the coagulant to be added to the raw water has + ions, if the coagulant is added to the raw water, an electrical neutralization reaction occurs. As a result, the flowing current I changes from − display to + display. Therefore, by measuring the streaming current I instead of measuring the zeta potential ζ, it is possible to determine whether or not the coagulant injected into the raw water is an appropriate amount.

Therefore, p of the inflowing raw water (sampling water) is
The H and water temperatures were kept constant, Kcl was dissolved in distilled water, and the streaming current value and the conductivity were measured, and the formula (3) was obtained. I [sigma] =-Ko (3) where [sigma] o is the electrical conductivity and Ko is a positive constant. FIG. 2 shows the correlation between the flowing current value I and the conductivity σ according to the equation (3).
Shown in. The description of FIG. 2 will be given later.

Further, the pH of the raw inflow water (sampling water)
And when the water temperature is constant, the turbidity is 10-100 with Karion.
Change the flow rate to 0 degrees and control the PAC injection amount so that the turbidity of the treated water is 2 degrees while injecting PAC (a type of coagulant, polyaluminum chloride), and the flowing current at the time of optimum injection of the PAC. When I and zeta potential ζ were measured,
Equations (4) and (5) could be obtained. I = Io (constant) ・ ・ ・ (4) ζ = ζo (constant) ・ ・ ・ (5) Formulas (4) and (5) are used to precipitate the suspended substance in the flocculant sedimentation tank 6 in FIG. It is established when the turbidity of the supernatant water after separation is equal to or lower than a target turbidity (for example, 1 degree) and constant.

As shown in FIG. 2, the SC value (flowing current value as the set point of the control target) Io in fine weather is Io = -2, and the conductivity σo in fine weather is σo = 150 μs /
cm, and the electrical conductivity σ n during rainfall is 100 μs / cm
Let's say In order to calculate the correction set point Is at that time, first, In (current value to be corrected) can be obtained from Expression (3) by Expression (6). In = Io × σo / σn (6) ∴In = −2 × 150/100 = −3

By determining In by the equation (6), the driving force ΔI of the chemical injection pump 2 can be defined by the equation (7). ΔI = Io −In (7) ∴ΔI = −2 + 3 = 1

The corrected set point Is can be defined by the equation (8). Is = Io + ΔI = Io + Io−In = 2Io−In ∴Is = −2 × 2 + 3 = −1 (8)

Here, since the SC value is usually displayed as −, it is particularly important to judge whether the pump driving force ΔI is positive (+) or negative (−), as in the equation (7). is there. Therefore, the correlation of the set point between the flowing current value I and the conductivity σ is shown in FIG. In FIG. 3, Io:
SC value (set point) in fine weather, In: SC value during calculation, σo: conductivity in fine weather, σn: conductivity other than σo, ΔI: pump driving force As described above, it can be obtained by the equation (8). Now, in FIG. 3, if the SC value during rainfall is kept the same as the SC value during fine weather, the inflowing raw water at the time of rainfall is diluted with rainwater. Controlling the amount results in a lack of coagulant injection (drug dosing), which has been confirmed in actual plants.

Therefore, in the first embodiment of the present invention, P
Based on the conductivity measurement value input from the electric conductivity 10 and the streaming current value input from the streaming ammeter 11, the ID controller 12 adjusts the coagulant injection amount to the inflowing raw water to the optimum amount, and the chemical injection pump 2 Is automatically controlled.

Next, the automatic control operation of the chemical injection pump 2 will be described with reference to the flowchart of FIG. First, in step ST1, it is determined whether or not the PID controller 12 is inputting operation signals of a raw water intake pump (not shown) for taking raw water to be purified into the landing well 1 and the chemical injection pump 2. However, when the operation signal is input, step ST
Go to 2. In step ST2, the conductivity σo has a constant relationship with the flowing current value Io during fine weather (when the coagulant is optimally injected).
Σ o = stable is determined, and if so, the process proceeds to step ST3.

In step ST3, the PID controller 1
2 is the streaming current measurement value i input from the streaming ammeter 11,
The flow current value Io at the set point set in the PID controller 12 is compared to determine whether i≤Io,
When i≤Io, the process proceeds to step ST4, where i≤Io
If not, the process proceeds to step ST8.

In step ST4, the PID controller 12 outputs a pump control command signal to the chemical injection pump 2 so as to increase the coagulant injection amount with respect to the inflow raw water, so that the coagulant injection amount depends on the property of the inflow raw water. The drive of the chemical injection pump 12 is controlled so that the optimum amount is obtained. On the other hand, in step ST8, the PID controller 12 outputs a pump control command signal to the chemical injection pump 12 so as to reduce the coagulant injection amount to the inflow raw water, so that the coagulant injection amount corresponds to the property of the inflow raw water. The chemical injection pump 12 so that the optimum amount is obtained.
Control the drive of.

On the other hand, when the judgment result in step ST2 is σ o = unstable, the process proceeds to step ST5. In this step ST5, the calculation according to the equation (6), that is, the calculation of In = Io * [sigma] o / [sigma] n is performed and then the process proceeds to step ST6. In this step ST6, In obtained in step ST5 is subtracted from Io, that is, the pump driving force ΔI is obtained by the equation (7), and then step ST7
Proceed to. In this step ST7, it is judged whether Is obtained by the equation (8) is i ≦ Io + ΔI = Is. If the result of the judgment is i ≦ Io + ΔI = Is, the process proceeds to step ST4. The drive of the chemical injection pump 2 is controlled to increase the coagulant injection amount, and when i ≦ Io + ΔI = Is is not satisfied, the process proceeds to step ST8 to control the drive of the chemical injection pump 2 to reduce the coagulant injection amount.

As described above, according to the first embodiment, the conductivity before the coagulant injection and the flowing current value after the coagulant injection at the optimal injection of the coagulant into the inflowing raw water are set as the management target. PID controller 12 as a point
Is set in advance, and the conductivity measurement value measured by the electric conductivity meter 10 and the flow current measurement value measured by the flow ammeter 11 are input to the PID controller 12 to measure the conductivity. since the value and the flow collector Nagarehaka value is configured to control the driving of the chemical feeding, chemical dosing pump 2 so that the conductivity and flow current value of the set point, the coagulant injection amount for flowing raw water properties of the inflow raw water It is possible to automatically control the optimum injection amount according to the required amount, prevent insufficient or excessive injection of coagulant, reduce running cost of water purification treatment, improve water treatment efficiency, and improve reliability. It has the effect of improving.

Further, according to the first embodiment, the stable conductivity σo and the flow current value Io in the raw raw water in a steady state are set in the PID controller 12 as a set point at the time of optimal injection of the coagulant into the raw raw water. Conductivity measurement value σn and streaming ammeter 1 set and measured by the electric conductivity meter 10
The streaming current measurement value In measured in 1 is used as the PID controller 1
By inputting 2, when the property of the inflowing raw water largely changes due to, for example, rainfall or groundwater mixing, the set point is corrected so that the optimum coagulant injection amount according to the change is obtained, that is, the corrected set point. Is is automatically calculated based on the conductivity measurement value σn and the streaming current measurement value In when the raw water condition changes, and the conductivity measurement value σn and the streaming current measurement value In when the raw water condition changes are corrected by the correction. Since the driving of the chemical injection pump 2 is controlled to automatically control the coagulant injection amount so that the conductivity σo and the flow current value Io at the set point Is are obtained, even when the property of the inflowing raw water largely changes. There is an effect that the coagulant injection amount can be automatically controlled so that the coagulant injection amount is optimal according to the variation.

Furthermore, according to the first embodiment, the PI
The D controller 12 judges whether or not the conductivity σo at the time of optimum injection of the coagulant into the inflowing raw water is σo = stable, and σo
= When stable, the streaming current measurement value i based on the input signal from the streaming current measuring means is compared with the streaming current value Io of the raw raw water at the time of optimal injection of the flocculant, and when i ≤ Io, the flocculant of the flocculant to the raw raw water is compared. The injection amount is increased, and when it is not, the injection amount of the coagulant is decreased and the driving of the chemical injection pump is controlled so that i becomes Is. Therefore, even if the property of the inflowing raw water changes, Accordingly, there is an effect that the coagulant injection amount for the inflowing raw water can be increased or decreased to automatically control the coagulant injection amount when the property of the inflowing raw water changes to be the optimum amount.

Embodiment 2. FIG. 5 is a schematic block diagram showing a coagulant automatic injection device for water purification according to Embodiment 2 of the present invention. The same parts as those in FIG. In FIG. 5, 8 is a flow meter that measures the inflow amount of raw water and outputs the measured value signal to the PID controller 12, and 9 is the measured value signal PID controller that measures the turbidity of the inflowing raw water before coagulant injection. It is a turbidimeter that outputs to 12.

That is, in the second embodiment, the measured value signals from the flowmeter 8, the turbidity meter 9 and the same electric conductivity 10 and flowing ammeter 11 as in the case of the first embodiment are PID adjusted. By inputting a total of 12, the P
The ID controller 12 controls the turbidity based on the raw water inflow measurement value input from the flow meter 8 and the turbidity measurement value input from the turbidity meter 9, and the electric conductivity as in the case of the first embodiment. The flow rate current is controlled at the same time based on the conductivity measurement value input from the rate meter 10 and the flow current measurement value input from the flow current meter 11, and by the control, the coagulant injection amount to the inflow raw water is optimized. The chemical injection pump 2 is configured to be automatically controlled as described above.

The automatic control operation of the chemical injection pump 2 will be described with reference to the flow chart shown in FIG. First, in step ST1, similarly to the case of the first embodiment, it is determined whether or not the operation signals of the raw water intake pump (not shown) and the chemical injection pump 2 are input to the PID controller 12. When the operation signal is input, the process proceeds to step ST2.

In step ST2, the PID controller 12 inputs the raw water inflow measurement value from the flow meter 8 and the turbidity measurement value from the turbidity meter 9, respectively, so that the raw water inflow measurement value and the turbidity measurement are performed. After calculating the inflow rate of raw water × turbidity coefficient = A (amount of coagulant injection by turbidity control) based on the value, the process proceeds to step ST3.

In step ST3, as in step ST2 of FIG. 4 according to the first embodiment, it is determined whether σ o = stable, and when σ o = stable, the process proceeds to step ST4 to determine whether i ≦ Io. If i≤Io, the process proceeds to step ST5. If not i≤Io, the process proceeds to step ST12.

In step ST5, the PID controller 1
2 obtains the coagulant injection amount B to be increased by flowing current control based on the flowing current measurement value input from the flowing ammeter 11.
In step ST12, after the PID controller 12 obtains the reduction value of the coagulant injection amount B to be reduced by the flow current control based on the flow current measurement value input from the flow ammeter 11, the step ST5 and Step ST1
From 2 to step ST6, respectively. This step S
At T6, it is determined whether 0.8 (estimated value of coagulant injection amount B by SC control) × A ≦ B, and 0.8 × A ≦ B
In case of B, it proceeds to step ST8 to judge whether or not B ≦ 1.2 (estimated value of coagulant injection amount A by turbidity control) × A, and in case of B ≦ 1.2 × A, aggregation by SC control. A control signal for the amount of drug injection B is output to the drug injection pump 2, and when the determination result in step ST6 is not 0.8 × A ≦ B and the determination result in step ST8 is B ≦ 1.2 ×.
When it is not A, the process proceeds to step ST13 and the control signal of the coagulant injection amount A by turbidity control is output to the chemical injection pump 2, so that the coagulant injection amount with respect to the inflow raw water becomes the optimum injection amount according to the property of the inflow raw water. So that the drug delivery pump 2
Control automatically.

When the determination result in step ST3 is not σ o = stable, the process proceeds to step ST9 to calculate the SC value In which is in the process of correcting the set point, and then proceeds to step ST10 to drive the pump driving means ΔI.
Is calculated, and then in step ST11, i ≦ Io + ΔI = I
It is determined whether or not s, and as a result of the determination, i ≦ I
When o + ΔI = Is, the process proceeds to step ST5, where i ≦
When Io + ΔI = Is is not satisfied, the step ST12 is executed.
To step S6 from step ST6.
Through T8 or step ST6 and step ST7 to step ST13, the chemical injection pump 2 is automatically controlled so that the coagulant injection amount into the inflow raw water becomes an optimum injection amount according to the property of the inflow raw water.

Example. FIG. 7 shows raw water turbidity (degree), PAC injection rate (mg / l), and streaming current value (-) using the flow meter 8 and turbidity meter 9 and the electric conductivity meter 10 and streaming ammeter 12 in FIG. ), The flow rate of landing water (m3 /
FIG. 3 is a table showing the results of measuring h), electric conductivity (conductivity μs / cm), and turbidity (degree) at the outlet of a crossflow type sedimentation tank.
The turbidity in FIG. 7 is an example of measurement when there is rainfall from a state where the turbidity is 3 to 5 degrees in fine weather and the turbidity rises to nearly 40 degrees due to the rainfall. When the PAC injection rate was increased from 20 ppm to 45 ppm, the turbidity at the outlet of the sedimentation tank gradually increased, so that the turbidity could not be kept below the control target of 1 degree. It is apparent from FIG. 7 that the flowing current value at this time is almost horizontal and hardly changes, but the electric conductivity changes greatly. Here, when the average value of the flowing current value and the average value of the electric conductivity (conductivity) for the two days before the rainfall are respectively defined as Io σo, according to the equation (9), Io
= -3.4, σ o = 164 μs / cm, the shaded area in FIG. In = Ioσo / σn (9)

FIG. 8 is a table showing the correlation between the measured SC value and the SC value after correction by electric conductivity. As is clear from FIG. 8, the set point of the flowing current during rainfall is
It can be proved that it does not match the flowing current value in fine weather.

Therefore, in the second embodiment, as shown in FIG. 7, even if the electric conductivity fluctuates due to rainfall or the like, the electric conductivity is changed so that the flow current curve in FIG. 7 becomes substantially horizontal. to correct. Therefore, the chemical injection pump 2 may be automatically controlled so as not to cause insufficient chemical injection in the hatched portion in FIG.

According to the second embodiment described above, the flow current control and the turbidity control are combined, and either the flow current control or the turbidity control is automatically selected to automatically control the chemical injection pump. Since it is configured to be performed, even if the property of the inflowing raw water changes, the effect of further injecting the coagulant into the inflowing raw water is increased. That is, in the case of turbidity control, the coagulant injection amount is determined by the turbidity of the inflow raw water and the inflow water amount regardless of the pH and the water temperature of the inflow raw water, whereas in the case of the streaming current control, the landing well , Influence of residence time in coagulant mixing pond, and pH change of raw inflow water is SC
Since the value and the amplitude of the PAC injection rate are amplified, for example, by making each control responsible for 50% of the target value, highly reliable and more practical control of the coagulant injection amount is performed. The effect is that you can.

[0045]

As described above, according to the present invention, since the optimum coagulant injection rate is always determined by the coagulation-sedimentation reaction, it is possible to prevent insufficient or excessive injection of the coagulant into the inflowing raw water. There is an effect.

According to the present invention, even when the property of the inflowing raw water changes, especially when the property of the inflowing raw water changes due to rainfall or groundwater mixing, the coagulant injection ratio at the time of the change is automatically set to the optimum coagulant injection ratio according to the change of the raw water condition. There is an effect that it is possible to change the correction.

According to the present invention, the flow current control and the turbidity control are combined, and either the flow current control or the turbidity control is automatically selected to automatically control the chemical injection pump. Even if the property of the inflowing raw water changes, there is an effect that the accuracy of injecting the coagulant into the inflowing raw water is further increased.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing an automatic coagulant injection device for water purification according to Embodiment 1 of the present invention.

FIG. 2 is a characteristic diagram showing a correlation between a flowing current value I and a conductivity σ.

FIG. 3 is a characteristic diagram showing a set point correlation between a flowing current value I and a conductivity σ.

4 is a flow chart diagram for explaining an automatic control operation of the chemical injection pump in FIG. 1. FIG.

FIG. 5 is a schematic block diagram showing an automatic coagulant injection device for water purification according to Embodiment 2 of the present invention.

6 is a flow chart diagram for explaining an automatic control operation of the chemical injection pump in FIG.

FIG. 7 is a table showing measured results of turbidity of inflowing raw water, streaming current value, PAC injection rate, and the like.

FIG. 8 is a table showing a correlation between an actually measured SC value and an SC value after being corrected by electric conductivity.

[Explanation of symbols]

1 landing well 2 chemical pump 3 rapid stirring pond 4 Flock formation pond 5 coagulation sedimentation tank 7 distribution reservoir 8 flow meter 9 Turbidimeter 10 Electric conductivity meter 11 Flow ammeter 12 PID controller 13 Turbidimeter

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Katata 3-16-1, Shibaura, Minato-ku, Tokyo Inside Nishihara Watertech Co., Ltd. (56) Reference JP-A-6-304413 (JP, A) Kaihei 6-304414 (JP, A) JP 7-256008 (JP, A) JP 3-284303 (JP, A) JP 5-103910 (JP, A) JP 10-1009094 ( (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01D 21/00-21/34 C02F 1/00 C02F 1/52-1/56 G01N 27/10 G05D 21/02

Claims (3)

(57) [Claims] 1. In a coagulant automatic injection device for water purification, which automatically injects a coagulant into raw water to be purified water, a chemical injection pump for injecting a coagulant into inflow raw water and a conductivity of inflow raw water before coagulant injection Conductivity measuring means for measuring, current measuring means for measuring a flowing current value of the coagulant-mixed water after coagulant injection by the chemical injection pump, and respective measurement value signals from the conductivity measuring means and the current measuring means And a pump control means for controlling the driving of the chemical injection pump so that the coagulant injection amount is adjusted according to the property variation of the inflowing raw water based on the measured value signal, and the pump control means is a steady state. Condition
The inflow raw water conductivity σ o and the flowing current value I o are
At the time of optimal injection of the coagulant for the raw water inflow at its steady state
Is set as a set point, the streaming current I o
Conductivity σ o of the set point that changes with changes
The correction set point Is by correcting
Input signal from current measuring means and said conductivity measuring means
Calculated based on the input signal from the current measuring means
The flowing current measurement value i according to
The coagulant automatic injection device for water purification, which is characterized by controlling the drive of the chemical injection pump . 2. The pump control means determines whether or not the conductivity σo at the time of optimal injection of the coagulant into the inflowing raw water is σo = stable, and when σo = stable, the input signal from the flowing current measuring means. The flow current measured value i by the flow rate is compared with the flow current value Io of the raw raw water at the time of optimal injection of the coagulant, and when i ≦ Io, the injection amount of the coagulant is increased with respect to the inflow raw water, and when not, the injection amount of the coagulant is injected. the reduced and i is a water purification flocculants automatic injection device according to claim 1, characterized in that is adapted to control the driving of the chemical feeding, chemical dosing pump so that is. 3. The pump control means, when σo = unstable, calculates In = Io × σo / σn and then ΔI = Io.
-In is calculated, and then it is determined whether or not i≤Io + ΔI = Is. When i≤Io + ΔI = Is, the increase value of the coagulant injection amount is calculated, and otherwise i is Is. It is characterized in that it calculates a reduction value of the coagulant injection amount, and outputs a turbidity control signal or a streaming current control signal based on the increase value and the reduction value of the coagulant injection amount to the chemical injection pump. The coagulant automatic injection device for water purification according to claim 1 .