JP2020175346A - Residual chlorine removal method, control device of residual chlorine removal system, and residual chlorine removal system - Google Patents

Abstract

To provide a residual chlorine removal method, a control device of a residual chlorine removal system and a residual chlorine removal system capable of appropriately controlling a supply amount of a reducing agent by ORP measurement in consideration of an effect of changes in pH in removing residual chlorine for supplying a reducing agent to treated water containing residual chlorine.SOLUTION: A residual chlorine removal method, a control device of residual chlorine system, and a residual chlorine removal system include an arithmetic control of supplying a reducing agent to a water to be treated which contains residual chlorine, correction of the ORP of the water to be treated based on the measured ORP value and pH of the water to be treated, and a control of an amount of supply of the reducing agent by the corrected ORP value. According to the present invention, it is possible to obtain a corrected value of ORP in consideration of an effect of pH. It is possible to appropriately control an amount of supply of the reducing agent based on the ORP value. In addition, in residual chlorine removal, it is possible to control excessive supply of the reducing agent to residual chlorine.SELECTED DRAWING: Figure 1

Description

The present invention relates to a residual chlorine removing method, a control device for a residual chlorine removing system, and a residual chlorine removing system. The present invention also relates to a residual chlorine removing method for performing a reduction treatment with a reducing agent, a control device for a residual chlorine removing system, and a residual chlorine removing system.

Chlorine agents are used as bacterial growth inhibitors and sterilizers in water treatment facilities, or as oxidizing agents in odor treatment. At this time, in order to avoid a shortage of chlorine agent in the water to be treated, it is necessary to supply an excessive amount of chlorine agent, but the chlorine remaining in the water to be treated (hereinafter referred to as "residual chlorine") is sent to the environment. Since there is a risk of adverse effects and harm to humans and organisms, it is not possible to release treated water containing excess residual chlorine into public water areas. Therefore, it is necessary to remove residual chlorine in the water to be treated.

As a method for removing residual chlorine in the water to be treated, an adsorbent such as activated carbon is known, but there are problems that it is difficult to judge the performance deterioration of the adsorbent and the cost is high.
Further, as another method for removing residual chlorine, it is known that a reducing agent is supplied to the residual chlorine to chemically remove it.

For example, Patent Document 1 describes a method for controlling the residual chlorine concentration in a chlorine removing method for supplying a reducing agent to water containing chlorine. Further, in Patent Document 1, the redox potential (hereinafter referred to as "ORP") of water containing chlorine to which a reducing agent is supplied is measured, and the reducing agent is supplied based on the measured value of the measured ORP and its change. It is stated that the situation is to be determined.

Japanese Unexamined Patent Publication No. 2004-33800

When the reducing agent is supplied to the residual chlorine to remove the residual chlorine, if the reducing agent is excessively supplied to the residual chlorine, the reducing agent will remain. In this case, there is a problem that the reducing agent component cannot be released into public water areas, so it is necessary to appropriately control the supply amount of the reducing agent with respect to the residual chlorine.

According to Patent Document 1, it is possible to determine whether or not the supply status of the reducing agent is properly performed by measuring the ORP when the reducing agent is supplied to the residual chlorine to remove the residual chlorine. Are listed.

On the other hand, when the reducing agent is supplied to the water to be treated containing residual chlorine, the present inventors may change the pH of the water to be treated due to the influence of the reducing agent. At this time, the change in the ORP value and the reducing agent We obtained the finding that the supply amount of the reducing agent cannot be controlled correctly because it is not linked to the supply status.

Although the ORP value is affected by pH, Patent Document 1 does not describe the effect of pH on the measurement of ORP, and does not consider the effect of pH fluctuation on the ORP value. Therefore, it is difficult to appropriately control the supply amount of the reducing agent with respect to the residual chlorine by the method described in Patent Document 1.

In particular, when a reducing agent containing sulfite ion or hydrogen sulfite ion is used, the dissociation state in the water to be treated differs depending on the pH. Therefore, in order to control the supply amount of the reducing agent with respect to the residual chlorine by measuring the ORP, it is necessary to consider the dissociation state of the reducing agent due to pH fluctuation.

An object of the present invention is that in removing residual chlorine for supplying a reducing agent to water to be treated containing residual chlorine, the amount of the reducing agent supplied can be appropriately controlled by ORP measurement in consideration of the influence of a change in pH. To provide a chlorine removal method, a control device for a residual chlorine removal system, and a residual chlorine removal system.

As a result of diligent studies on the above problems, the present inventor measured ORP and pH in removing residual chlorine by supplying a reducing agent to the water to be treated containing residual chlorine, and set the measured value of pH as one of the parameters. , The present invention has been completed by finding that the influence of pH fluctuation on the ORP value can be eliminated by correcting the ORP value and the supply amount of the reducing agent can be appropriately controlled by the ORP measurement.
That is, the present invention is the following residual chlorine removing method, a control device for a residual chlorine removing system, and a residual chlorine removing system.

The method for removing residual chlorine of the present invention for solving the above problems is a method for removing residual chlorine that reduces the water to be treated containing residual chlorine, and adds sulfite ion or hydrogen sulfite ion to the water to be treated containing residual chlorine. An ORP value measured using the reduction treatment step of supplying the containing reducing agent, the measurement step of measuring the oxidation-reduction potential (ORP) and pH of the water to be treated after the reduction treatment step, and the pH value measured in the measurement step. Is provided, and a calculation control step for adjusting the supply amount of the reducing agent in the reduction treatment based on the corrected ORP value is provided.
In the method for removing residual chlorine of the present invention, the ORP and pH are measured in the measurement step, and the ORP value is corrected in the arithmetic control step based on the measurement result to obtain the correction value of the ORP in consideration of the influence of pH. be able to. Further, the calculation control step makes it possible to appropriately grasp the timing of controlling the supply amount of the reducing agent, and it is possible to appropriately control the supply amount of the reducing agent. This makes it possible to suppress the excessive supply of the reducing agent to the residual chlorine in the removal of the residual chlorine.

Further, as one embodiment of the method for removing residual chlorine of the present invention, the correction of the ORP value in the calculation control step is performed with respect to a reducing agent in which the valence of the reducing agent changes with a change in pH during the reduction treatment step. It has a feature that it is performed based on a correction formula in which the coefficient in the Nernst equation is changed by using the acid dissociation constant of.
According to this feature, the ORP value can be corrected even for a reducing agent containing sulfite ion or hydrogen sulfite ion whose valence according to the dissociated state of the reducing agent differs depending on the pH. This makes it possible to improve the accuracy of the correction of the ORP value.

Further, as one embodiment of the residual chlorine removing method of the present invention, the ORP value in the calculation control step is corrected based on the correction formula represented by the following formula.
_{E C = E M -2.3026 (RT} / z A F) (pH 0 -pH A)
Here, z _A = (2 × 10 ^(pHA-7.2) +1) / (10 ^(pHA-7.2) +1) …… (formula)
Also, _{E C} is corrected ORP value (correction ORP value), _{E M} is the measured ORP value (ORP measured value), pH value before pH ₀ is adding a reducing agent, a pH value pH _A is to be measured Shown. Further, R is the molar gas constant (= 8.314 J / K · mol), F is the Faraday constant (= 96485 C / mol), z _A is the average ionic valence, and T is the absolute temperature (unit: K). ..
According to this feature, even for a reducing agent containing sulfite ion or hydrogen sulfite ion, which has a different valence depending on the pH of the reducing agent in the dissociated state, continuous calculation is performed without changing the correction formula. Can be done. As a result, the arithmetic processing for correcting the ORP value can be simplified, and the processing speed related to the arithmetic processing can be increased.

Further, as one embodiment of the method for removing residual chlorine of the present invention, in the measurement step, the temperature of the water to be treated after the reduction treatment step is further added, and in the correction of the ORP value in the calculation control step, the measurement step It has a feature that the value of the temperature measured in is also used.
According to this feature, the ORP value can be corrected by using the temperature of the water to be treated as a parameter. This makes it possible to improve the accuracy of the correction of the ORP value.

Further, the control device for the residual chlorine removal system of the present invention for solving the above problems is a control device for the residual chlorine removal system provided in the residual chlorine removal system that reduces the water to be treated containing the residual chlorine. The residual chlorine removal system includes a reaction tank for introducing water to be treated containing residual chlorine, and a reducing agent supply unit for supplying a reducing agent containing sulfite ion or hydrogen sulfite ion to the reaction tank. Using the measuring unit that measures the oxidation-reduction potential (ORP) and pH of the water to be treated in the tank and the pH value measured by the measuring unit, the measured ORP value is corrected, and the reduction is performed based on the corrected ORP value. It is characterized by including an arithmetic control unit that adjusts the supply amount of the reducing agent by the agent addition unit.
The control device of the residual chlorine removal system of the present invention measures the ORP and pH of the reaction tank in the residual chlorine removal system, and corrects the ORP value based on the measurement result to take the influence of pH into consideration. A correction value can be obtained. Further, the arithmetic control unit can appropriately grasp the timing of controlling the supply amount of the reducing agent, and can appropriately control the supply amount of the reducing agent. This makes it possible to suppress the excessive supply of the reducing agent to the residual chlorine in the removal of the residual chlorine.

Further, in one embodiment of the control device of the residual chlorine removal system of the present invention, in the correction of the ORP value in the arithmetic control unit, the valence of the reducing agent changes with the change in pH when the reducing agent is added. It has a feature that it is carried out based on a correction formula in which the coefficient in the Nernst equation is changed by using the acid dissociation constant of the reducing agent.
According to this feature, the ORP value can be corrected even for a reducing agent containing sulfite ion or hydrogen sulfite ion whose valence according to the dissociated state of the reducing agent differs depending on the pH. This makes it possible to improve the accuracy of the correction of the ORP value.

Further, one embodiment of the control device of the residual chlorine removal system of the present invention is characterized in that the correction of the ORP value in the arithmetic control unit is performed based on the correction formula represented by the following formula.
_{E C = E M -2.3026 (RT} / z A F) (pH 0 -pH A)
Here, z _A = (2 × 10 ^(pHA-7.2) +1) / (10 ^(pHA-7.2) +1) …… (formula)
Also, _{E C} is corrected ORP value (correction ORP value), _{E M} is the measured ORP value (ORP measured value), pH value before pH ₀ is adding a reducing agent, a pH value pH _A is to be measured Shown. Further, R is the molar gas constant (= 8.314 J / K · mol), F is the Faraday constant (= 96485 C / mol), z _A is the average ionic valence, and T is the absolute temperature (unit: K). ..
According to this feature, even for a reducing agent containing sulfite ion or hydrogen sulfite ion, which has a different valence depending on the pH of the reducing agent in the dissociated state, continuous calculation is performed without changing the correction formula. Can be done. As a result, the arithmetic processing for correcting the ORP value can be simplified, and the processing speed related to the arithmetic processing can be increased.

Further, as one embodiment of the control device of the residual chlorine removal system of the present invention, the measurement unit further measures the temperature of the water to be treated in the reaction vessel, and the calculation control unit corrects the ORP value. It has the feature that the value of the temperature measured by the measuring unit is also used.
According to this feature, the ORP value can be corrected by using the temperature of the water to be treated as a parameter. This makes it possible to improve the accuracy of the correction of the ORP value.

The residual chlorine removal system of the present invention for solving the above problems is a residual chlorine removal system that reduces the water to be treated containing residual chlorine, and is a reaction tank into which the water to be treated containing residual chlorine is introduced. It is characterized by including a reducing agent supply unit that supplies a reducing agent containing a sulfite ion or a hydrogen sulfite ion to the reaction vessel, and any one of the above-mentioned control devices.
The residual chlorine removal system of the present invention measures the ORP and pH of the reaction vessel, and based on the measurement result, corrects the ORP value by the control device to obtain the correction value of ORP considering the influence of pH. Can be done. Further, the arithmetic control unit of the control device makes it possible to appropriately grasp the timing of controlling the supply amount of the reducing agent, and it is possible to appropriately control the supply amount of the reducing agent. This makes it possible to suppress the excessive supply of the reducing agent to the residual chlorine in the removal of the residual chlorine.

According to the present invention, in removing residual chlorine for supplying a reducing agent to water to be treated containing residual chlorine, the amount of the reducing agent supplied can be appropriately controlled by ORP measurement in consideration of the influence of a change in pH. A chlorine removal method, a control device for a residual chlorine removal system, and a residual chlorine removal system can be provided.

It is the schematic explanatory drawing of the residual chlorine removal system in 1st Embodiment of this invention. It is a schematic diagram which shows the time-dependent change of pH _A , the measured value of ORP before correction, and the corrected ORP value after correction in the 1st Embodiment of this invention. It is a schematic diagram which shows the time-dependent change of the corrected ORP value which concerns on the residual chlorine removal method in 1st Embodiment of this invention. It is the schematic explanatory drawing of the residual chlorine removal system in the 2nd Embodiment of this invention.

The residual chlorine removing method, the control device of the residual chlorine removing system, and the residual chlorine removing system of the present invention are suitably used in the reduction treatment of water to be treated containing residual chlorine.

The water to be treated, which is the object of the present invention, may be any water containing residual chlorine and is not particularly limited. The water to be treated may be wastewater / wastewater discharged from various factories, treatment plants, etc., or may be such as circulating water used in plants, etc. In addition to industrial water, water that is sterilized and sterilized with a chlorine agent, such as river water, clean water, and water stored in tanks such as pools and public baths, can be mentioned. Here, the residual chlorine refers to a chlorine compound that effectively acts on sterilization, sterilization, and oxidation reaction of substances contained in water. Further, from the viewpoint of further exerting the effect of the present invention, it is preferable that the water to be treated, which is the subject of the present invention, mainly contains free chlorine as residual chlorine. Here, free chlorine refers to residual chlorine existing in water as chlorine gas, hypochlorous acid and hypochlorite ions. Examples of such water to be treated include water to be treated using sodium hypochlorite as a chlorinating agent. The water to be treated of the present invention is not limited to this, and any water to be treated containing chlorine that can be reduced with a reducing agent is the subject of the present invention.

Hereinafter, the method for removing residual chlorine, the control device for the residual chlorine removal system, and the embodiment of the residual chlorine removal system according to the present invention will be described in detail with reference to the drawings. The contents described in the following embodiments are merely exemplified for explaining the residual chlorine removing method, the control device of the residual chlorine removing system, and the residual chlorine removing system according to the present invention, and are limited thereto. It's not a thing.

[First Embodiment]
(Residual chlorine removal system)
FIG. 1 is a schematic explanatory view of a residual chlorine removal system according to the first embodiment of the present invention.
As shown in FIG. 1, the residual chlorine removal system 1a according to the present invention includes a reaction tank 2 for introducing water W to be treated containing residual chlorine, a reducing agent supply unit 3 for supplying a reducing agent R, and an ORP measuring unit. 4, a pH measuring unit 5, and an arithmetic control unit 6 are provided. Further, a line L1 which is an introduction pipe for introducing the water to be treated W into the reaction tank 2 and a line L2 which is a discharge pipe for discharging the treated water W1 discharged from the reaction tank 2 to the outside of the system are provided. Have. The arrow of the alternate long and short dash line in FIG. 1 indicates that they are connected in an input or controllable manner.

The reaction tank 2 is for reacting the water to be treated W containing residual chlorine with the reducing agent R to reduce the residual chlorine.
As shown in FIG. 1, the water W to be treated is supplied to the reaction tank 2 via the line L1 provided in the reaction tank 2. Further, the reducing agent R is supplied to the reaction tank 2 from the reducing agent supply unit 3 described later, and the residual chlorine in the water to be treated W is reduced. The treated water W1 after the reduction treatment is discharged from the reaction tank 2 via the line L2 provided in the reaction tank 2. The reaction tank 2 may be provided with a stirrer 21 inside. This makes it possible to promote the reaction between the water to be treated W and the reducing agent R.

The reducing agent supply unit 3 is for supplying the reducing agent R to the reaction tank 2.
As shown in FIG. 1, the reducing agent supply unit 3 includes a reducing agent storage tank 31 for storing the reducing agent R, a reducing agent supply line 32 for supplying the reducing agent R to the reaction tank 2, and a supply amount of the reducing agent R. The reducing agent supply amount control unit 33 for controlling the above is provided.

The reducing agent storage tank 31 is not particularly limited as long as it can store the reducing agent R. For example, any one can stably store the solid or liquid reducing agent R, and examples thereof include a light-shielded cylindrical body and a rectangular parallelepiped tank. Further, it is particularly preferable to have chemical resistance to the reducing agent R.

Examples of the reducing agent R stored in the reducing agent storage tank 31 include those containing sulfite ion or hydrogen sulfite ion. More specifically, sodium thiosulfate, sodium sulfite, sodium hydrogen sulfite and the like can be mentioned. By using these as the reducing agent R, harmless sulfate ions can be generated after the reaction with the residual chlorine. Further, since those containing sulfite ion or hydrogen sulfite ion have strong reducing power, the reaction time with the residual chlorine in the water to be treated W can be shortened by using these as the reducing agent R, and the residual chlorine can be shortened. The removal can proceed in a short time.
The reducing agent R may be supplied as a solid to the water to be treated W in the reaction tank 2, but the stability of the reducing agent R and the reaction rate with the residual chlorine in the water to be treated W may be determined. In view, it is preferable that the reducing agent R is stored as an aqueous solution in the reducing agent storage tank 31 and supplied to the water to be treated W in the reaction tank 2.

The reducing agent supply line 32 is a transportation pipe for supplying the reducing agent R to the reaction tank 2.
Further, the reducing agent supply amount control unit 33 is for controlling the supply amount of the reducing agent R by input from the arithmetic control unit 6 described later, and is provided on the reducing agent supply line 32.

When the reducing agent R is a solution, the reducing agent supply amount control unit 33 controls the flow rate in the reducing agent supply line 32, such as a pump and a flow rate control valve. At this time, the flow rate in the reducing agent supply amount control unit 33 is controlled by repeatedly executing the supply and stop of the reducing agent R by the on / off control of the pump, controlling the rotation speed of the pump by the inverter, and transferring by the pump. The supply amount of the reducing agent R may be changed continuously or discontinuously by controlling the volume amount or the opening / closing degree of the flow rate control valve.
When the reducing agent R is a solid, the reducing agent supply amount control unit 33 includes a valve, a supply hopper, and the like. At this time, the control of the supply amount of the reducing agent R in the reducing agent supply amount control unit 33 is to repeatedly supply and stop the reducing agent R by controlling the opening and closing of the valve and the supply hopper, and to open and close the valve and the supply hopper. The supply amount of the reducing agent R may be changed continuously or discontinuously by controlling the degree.

The ORP measuring unit 4 measures the ORP value of the water to be treated W in the reaction tank 2. Further, the ORP measurement unit 4 is connected to the calculation control unit 6 so as to be input, and the ORP value data obtained by the ORP measurement unit 4 is input to the calculation control unit 6.

The ORP measuring unit 4 can use a known ORP meter capable of measuring the ORP value. For example, one having a working electrode and a reference electrode and determining the ORP based on the potential difference generated between the working electrode and the reference electrode can be used. At this time, a platinum electrode is used as the working electrode, and a silver-silver chloride electrode or a standard hydrogen electrode is used as the reference electrode. The ORP measuring unit 4 is not limited to this, and may be any one capable of stably measuring the ORP value of the water to be treated W.

The pH measuring unit 5 measures the pH value of the water to be treated W in the reaction vessel 2. Further, the pH measuring unit 5 is connected to the arithmetic control unit 6 so as to be input, and the pH value data obtained by the pH measuring unit 5 is input to the arithmetic control unit 6.

As the pH measuring unit 5, a known pH meter capable of measuring a pH value can be used. For example, one using a glass electrode or one using a colorimetric method using an indicator can be used. Since continuous measurement is easy, it is preferable that the pH measuring unit 5 uses a glass electrode. The pH measuring unit 5 is not limited to this, and may be any one capable of stably measuring the pH value of the water to be treated W.

The arithmetic control unit 6 controls the reducing agent supply amount control unit 33 based on the measurement data from the ORP measurement unit 4 and the pH measurement unit 5.
The calculation control unit 6 includes a calculation unit 61 and a control unit 62.

The calculation unit 61 corrects the ORP value based on the measurement data from the ORP measurement unit 4 and the pH measurement unit 5, and supplies or stops the supply of the reducing agent R based on the obtained corrected ORP value with time. It is to judge the timing of.
The calculation unit 61 may include, for example, a calculation means for calculating the amount of change in the ORP value due to the pH value and the corrected ORP value based on the formula (correction formula) required for the correction of the ORP value. The configuration is not particularly limited. Specific examples of the arithmetic unit 61 include a computer equipped with a CPU, ROM, RAM, HDD, etc., a sequencer (PLC (Programmable Logic Controller)), and the like.

The correction formula used in the calculation unit 61 will be described.
The amount of change (ΔE) in the ORP value affected by pH can be calculated based on the Nernst equation (Equation 1) shown below.
Here, [H ₀ ] is the hydrogen ion concentration (unit: mol / L) before the pH change (before adding the reducing agent), and pH ₀ (= −ln [H ₀ ]) is the pH value at this time. Is shown. Further, [ _HA ] is the hydrogen ion concentration (unit: mol / L) actually measured after the pH change (after adding the reducing agent), and the pH _A (= -ln [ _HA ]) is at this time. It shows the pH value. Further, R is a molar gas constant (= 8.314 J / K · mol), F is a Faraday constant (= 96485 C / mol), z is an ionic valence, and T is an absolute temperature (unit: K).
Thus, after obtaining the Delta] E based on the equation 1, actually measured the ORP value (hereinafter, referred to as "ORP Found _{(E M)".)} From By subtracting Delta] E, corrected ORP value (hereinafter, referred to as "correction ORP value _{(E C)".)} can be obtained (equation 2).

On the other hand, the ionic valence z in the above-mentioned formula 1 may change depending on the pH.
For example, sulfurous acid _(H 2 SO ₃₎ varies depending on the pH of dissociation state in water, as shown in the following equation, sulfur dioxide _(SO 2), bisulfite (HSO ₃ ^-), sulfite ion _(SO ^{3 2 -} ) Is known to take the form (Equation 3 and Equation 4).
Here, the acid dissociation constant _Ka1 in the formula 3 is 1.4 × ^10-2 (mol / L), and the acid dissociation constant _Ka2 in the formula 4 is 6.5 × ^10-8 (mol / L).
At this time, sulfite, pH <1.9 as (= _{pK a1)} in _{SO 2, 1.9 <pH <7.2} (= pK a2) in HSO ₃ ^- as further pH> 7.2 in SO ₃ It means that the ratio that exists as ^2- will increase. At a pH having a high proportion of sulfur dioxide (SO ₂ ), SO ₂ is vaporized and cannot be used as a reducing agent R. Therefore, in this embodiment, the correction of the ORP value when the pH is in the range of at least 1.9 or more will be described.

When the liquid W to be treated is alkaline, if the reduction treatment is carried out with acidic sodium sulfite as the reducing agent R, the pH of the water W to be treated decreases as the reduction treatment progresses, and the pH may pass through pH 7.2. At this time, as shown in Equation 4, sulfite ion _(SO ^{3 2-)} is bisulfite (HSO ₃ ^-) changes to, ionic valence z in Equation 1 changes from 2 to 1.

Moreover, sulfur dioxide _(SO 2) in which sulphite is generated to dissociate, bisulfite ion (HSO ₃ ^-), the sulfite ions _(SO ^{3 2-),} since the sum of each substance amount is constant, sulfite ion ( SO ₃ ^2-) and bisulfite ions (HSO ₃ ^- ratio of the amount of substance of) (material weight ratio), gradually changes before and after pH 7.2.
Therefore, in order to perform continuous calculation in the pH region accompanied by a change in the ionic valence z, the ionic valence z was averaged.

First, a certain pH value (pH _X) sulfite ion in _(SO ^{3 2-)} and bisulfite ions (HSO ₃ ^-) for the ratio of the amounts of substances, the substance amount ratio of sulfite ion _(SO ^{3 2-)} α, bisulfite ion (HSO 3 ^_-) If the amount of substance ratio was β of, so the equations 5 and 6 below.
At this time, sulfur dioxide (SO ₂ ) can be considered to be almost absent in the system. Therefore, α + β = 1 holds.

Assuming that the ionic valence z is determined by the substance amount ratio described above, the average ionic valence z _A is represented by the following formula 7.

Those obtained by substituting z _A represented by the formula 7 as ionic valence z in Equation 1, is used as the correction equation for obtaining the correction ORP value (E _C) (Equation 8).
The constants and variables other than z _A in the equation 8 are the same as those in the equation 1.

Calculating unit 61, using equation 8, and calculates the correction ORP value _{(E C)} from the actually measured the pH value (pH _A) and ORP measured value _{(E M).} At this time, by using the formula 8, it is possible to perform continuous arithmetic processing without changing the correction formula even if the valence of the reducing agent R in the dissociated state differs depending on the pH.
The arithmetic unit 61, based on the temporal change of the calculated correction ORP value (E _C), to determine the timing of the supply or supply stop of the reducing agent R. Then, the determination result is input to the control unit 62.

The control unit 62 controls the supply amount of the reducing agent R with respect to the residual chlorine in the water to be treated W based on the determination result by the calculation unit 61.

In the control unit 62, a determination regarding the supply or supply stop of the reducing agent R is input from the calculation unit 61, and the reducing agent supply amount control unit 33 is controlled according to the determination result to supply or stop the supply or supply of the reducing agent R. Do.
As a means for supplying or stopping the supply of the reducing agent R, for example, the control means described in the reducing agent supply amount control unit 33 can be used. Specifically, for example, switching on / off of the pump of the reducing agent supply amount control unit 33, adjusting the flow rate of the pump, and the like can be mentioned.

FIG. 2 is a schematic view showing changes over time in pH and ORP when the reducing agent R is supplied to the water to be treated W containing residual chlorine in the residual chlorine removing system 1a of the present embodiment. The horizontal axis of FIG. 2 shows the passage of time, the vertical axis on the left side shows the ORP value, and the vertical axis on the right side shows the pH value. The broken line in Figure 2 shows the ORP measured value before correction _{(E M),} the solid line indicates the correction ORP value after correction according to equation 8 _{(E C).} The thick line in FIG. 2 indicates the actually measured pH value (pH _A ).

When the reducing agent R is supplied into the water to be treated W, the ORP value decreases as the reaction between the residual chlorine and the reducing agent R proceeds. Therefore, by stopping the supply of the reducing agent R when the decrease in the ORP value is detected, the supply amount of the reducing agent R can be appropriately controlled with respect to the residual chlorine.

However, as shown in FIG. 2, the uncorrected ORP measured value _{(E M)} is with decreasing pH _A in affected to variations in pH, during the supply of the reducing agent R (time A in FIG. 2) ORP The value of is increased. In particular, high concentration of residual chlorine, if the supply amount of the reducing agent R increases, since the large variations in pH, effect of pH _A against ORP measured value before correction (E _M) is increased. Therefore, even using the uncorrected ORP measured value (E _M), it is impossible to properly grasp the timing of stopping the supply of the reducing agent R in the removal of residual chlorine.

On the other hand, as shown in FIG. 2, the correction ORP value after correction (E _C) is not affected by variations in pH, after a predetermined time has elapsed from the supply of the reducing agent R (time B in FIG. 2), ORP The value of has decreased. That is, it can be seen that at time B, the necessary reducing agent R was supplied to the residual chlorine in the water to be treated W, and the reduction treatment was completed. At this time, the calculation unit 61 determines to stop the supply of the reducing agent R, and the determination result is input to the control unit 62, so that it is possible to suppress the excessive supply of the reducing agent R. ..
Therefore, the calculated ORP value can be obtained in consideration of the influence of pH by correcting the actually measured ORP value using the equation 8 in the calculation unit 61. As a result, the calculation unit 61 can appropriately grasp the timing of controlling the supply amount of the reducing agent R, and the control unit 62 can appropriately control the supply amount of the reducing agent R.

The configuration of the ORP measuring unit 4, the pH measuring unit 5, and the arithmetic control unit 6 in the present embodiment can be independent as the control device according to the present invention. This controller can be applied to existing residual chlorine removal systems. Thereby, in the existing residual chlorine removing system, the residual chlorine removing system and the residual chlorine removing method of the present invention can be provided by a simple installation work.

(Residual chlorine removal method)
A method for removing residual chlorine using the residual chlorine removal system in this embodiment will be described. The residual chlorine removal system has been described based on the structure shown in FIG. 1, but is not limited thereto.

Figure 3 is a schematic diagram showing changes with time of the correction ORP value after correction (E _C). The horizontal axis shows the passage of time, and the vertical axis shows the ORP value. Further, FIG. 3 also describes the time points at which the reducing agent R is supplied and stopped by the reducing agent supply amount control unit 33.

First, the reducing agent R is supplied to the water to be treated W containing residual chlorine in the reaction tank 2 by the reducing agent supply unit 3 (time A in FIG. 3). At this time, the reaction between the residual chlorine and the reducing agent R proceeds (reduction treatment step). Further, the ORP and pH in the reaction vessel 2 are measured by the ORP measuring unit 4 and the pH measuring unit 5, respectively (measurement step). At this time, the arithmetic unit 61 in the arithmetic control unit 6 performs a correction based on Equation 8 by using ORP measured value _{(E M)} and actually measured the pH value (pH _A), calculates a correction ORP value _{(E C)} (Calculation control step-1).

As the reduction treatment step progresses, the residual chlorine and the reducing agent R in the water W to be treated decrease, the required amount of the reducing agent R is supplied to the residual chlorine, and the reduction treatment is completed (in FIG. 3). At time B), the value of ORP decreases rapidly. At this time, if the supply of the reducing agent R is continued, the supply amount of the reducing agent R becomes excessive. Thus, the arithmetic unit 61, corrected by decreasing ORP value _{(E C)} are, upon reaching the lower reference value preset ORP value _{(E LS),} carry out a decision to stop the reduction treatment. Then, based on this determination result, the control unit 62 controls the reducing agent supply amount control unit 33 and stops the supply of the reducing agent R (calculation control step-2). At this time, at the time when the supply of the reducing agent R is stopped (time C in FIG. 3), it is preferable that the interval from the time B when the reduction treatment is completed is small. This makes it possible to suppress the excessive supply of the reducing agent R.

Further, the reaction vessel 2 from the treatment water W containing residual chlorine is supplied continuously, the correction ORP value in the reaction vessel 2 (E _{C) (and} ORP measured value (E _M)) again Rise. Re elevated correction ORP value _{(E C)} is, up to the limit reference value ORP value preset _{(E HS)} or decrease before the correction ORP value _{(E C),} calculation unit 61, a reduction treatment Make a decision to resume. Then, based on this determination result, the control unit 62 controls the reducing agent supply amount control unit 33, and restarts the supply of the reducing agent R at the time D in FIG. 3 (calculation control step-3). Then, in the arithmetic control step, by repeating the steps at time A (time D), time B, and time C, residual chlorine in the water to be treated W can be removed without excessively supplying the reducing agent R. It will be possible.

As described above, by using the residual chlorine removing method, the residual chlorine removing system and the control device thereof of the present embodiment, it is possible to grasp the fluctuation of the ORP value in consideration of the influence of pH, and the reducing agent in the reducing treatment. It becomes possible to appropriately control the supply amount. This makes it possible to suppress the excessive supply of the reducing agent in the removal of residual chlorine by the reduction treatment.

[Second Embodiment]
FIG. 4 is a schematic explanatory view of the residual chlorine removal system 1b according to the second embodiment of the present invention.
As shown in FIG. 4, the residual chlorine removal system 1b according to the present embodiment is the residual chlorine removal system 1a of the first embodiment to which the temperature measuring unit 7 is added. Further, the temperature measuring unit 7 is connected to the arithmetic control unit 6 so as to be inputtable.
Of the configurations of the residual chlorine removal system 1b in the present embodiment, the same configurations as those of the residual chlorine removal system 1a of the first embodiment will be omitted.

Residual chlorine removal system 1b of the present embodiment, the temperature in the reaction vessel 2 was measured by the temperature measuring unit 7, based on the measurement results, calculation of the correction ORP value in the operation control section 6 (E _C), and correction ORP performs control of the supply amount of the reducing agent R based on the value (E _C).

The temperature measuring unit 7 is not particularly limited as long as the temperature of the water to be treated W in the reaction vessel 2 can be measured. A known thermometer can be used. For example, the temperature measuring unit 7 may be provided with the detection portion in water, or may measure the temperature of the water surface. The temperature measuring unit 7 is not limited to this, and may be any one capable of stably measuring the temperature of the water to be treated W. Further, the temperature data obtained by the temperature measuring unit 7 is input to the arithmetic control unit 6.

When the temperature inside the reaction vessel 2 is stable, such as when the temperature obtained by the temperature measuring unit 7 is within a certain range in the calculation unit 61 of the calculation control unit 6, the absolute temperature T in the above equation 8 Can be treated as a constant.
On the other hand, when the temperature of the water to be treated W in the reaction tank 2 is not stable, such as when the temperature obtained by the temperature measuring unit 7 fluctuates, the temperature by the temperature measuring unit 7 is set to the absolute temperature T of the equation 8 as a variable. enter the measurement data, it is assumed that the correction of ORP measured value (E _M). Thus, using the calculation in consideration of the effects of changes in temperature, it is possible to determine the correction ORP value (E _C).

By grasping the temperature change in the reaction vessel 2 by the residual chlorine removal system 1b in the present embodiment and inputting it as a parameter in the correction formula shown as the formula 8, it is possible to correct the ORP value with higher accuracy. This makes it possible to more appropriately control the amount of the reducing agent supplied in the reduction treatment.

Further, using the residual chlorine removing system 1b of the present embodiment, the residual chlorine can be removed based on the same steps as the residual chlorine removing method described in the first embodiment. This makes it possible to more appropriately control the amount of the reducing agent supplied in the residual chlorine treatment method in which the reduction treatment is performed with the reducing agent.

Further, the configuration in which the temperature measuring unit 7 is added to the ORP measuring unit 4, the pH measuring unit 5, and the arithmetic control unit 6 in the present embodiment can be independent as the control device according to the present invention. This controller can be applied to existing residual chlorine removal systems. Thereby, in the existing residual chlorine removing system, the residual chlorine removing system and the residual chlorine removing method of the present invention can be provided by a simple installation work.

The above-described embodiment shows an example of a residual chlorine removing method, a residual chlorine removing system, and a control device thereof. The residual chlorine removing method, the residual chlorine removing system and the control device thereof according to the present invention are not limited to the above-described embodiment, and the residual chlorine according to the above-described embodiment is not changed as long as the gist described in the claims is not changed. The removal method, the residual chlorine removal system and its control device may be modified.

For example, in the present embodiment, those containing sulfite ion or hydrogen sulfite ion as a reducing agent have been described, but the present invention is not limited thereto. For example, a correction formula based on the Nernst equation is used for a reducing agent whose valence changes in the water to be treated W when the pH fluctuates in the reduction treatment, using the formula related to the average ionic valence. The residual chlorine removing method, the residual chlorine removing system and the control device thereof of the present embodiment can be preferably used.

Further, in the present embodiment, the water to be treated W containing residual chlorine to be treated is alkaline and the reducing agent is acidic, and the pH of the water to be treated W is changed from the alkaline side to the acidic side. Although the processing has been described, it is not limited to this. The residual chlorine removing method and the residual chlorine removing system of the present embodiment also apply to other reduction treatments in which the pH fluctuates due to the supply of the reducing agent and the pH value fluctuates via the value of the acid dissociation constant of the reducing agent. And its control device can be preferably used.

The residual chlorine removing method, the residual chlorine removing system and the control device thereof of the present invention are used for the reduction treatment of the water to be treated containing the residual chlorine. In particular, the residual chlorine removing method, the residual chlorine removing system and the control device thereof of the present invention are suitably used for the reduction treatment using a reducing agent whose dissociation state in the water to be treated changes depending on pH.

1a, 1b Residual chlorine removal system, 2 Reaction tank, 21 Stirrer, 3 Reducing agent supply unit, 31 Reducing agent storage tank, 32 Reducing agent supply line, 33 Reducing agent supply amount control unit, 4 ORP measurement unit, 5 pH measurement parts, 6 calculation control unit, 61 computing unit, 62 control unit, 7 temperature measuring unit, L1, L2 line, _{E C} correction ORP _value, E M ORP measured _value, the upper limit reference value E HS _ORP, the lower limit of E LS ORP Reference value, R reducing agent, W treated water, W1 treated water

Claims (9)

It is a residual chlorine removal method that reduces the water to be treated containing residual chlorine.
A reduction treatment step of supplying a reducing agent containing sulfite ions or hydrogen sulfite ions to water to be treated containing residual chlorine, and
A measurement step for measuring the redox potential (ORP) and pH of the water to be treated after the reduction treatment step,
It is characterized by including an arithmetic control step of correcting the ORP value measured by using the pH value measured in the measurement step and adjusting the supply amount of the reducing agent in the reduction treatment based on the corrected ORP value. Residual chlorine removal method. The correction of the ORP value in the calculation control step uses the acid dissociation constant of the reducing agent to change the coefficient in the Nernst equation for the one in which the valence of the reducing agent changes with the change in pH during the reduction treatment step. The method for removing residual chlorine according to claim 1, wherein the method is carried out based on the correction formula. The method for removing residual chlorine according to claim 1 or 2, wherein the correction of the ORP value in the calculation control step is performed based on the correction formula represented by the following formula.

_{E C = E M -2.3026 (RT} / z A F) (pH 0 -pH A)
Here, z _A = (2 × 10 ^(pHA-7.2) +1) / (10 ^(pHA-7.2) +1) …… (formula)

Also, _{E C} is corrected ORP value (correction ORP value), _{E M} is the measured ORP value (ORP measured value), pH value before pH ₀ is adding a reducing agent, a pH value pH _A is to be measured Shown. Further, R is the molar gas constant (= 8.314 J / K · mol), F is the Faraday constant (= 96485 C / mol), z _A is the average ionic valence, and T is the absolute temperature (unit: K). .. In the measurement step, the temperature of the water to be treated after the reduction treatment step is further added to be measured.
The method for removing residual chlorine according to any one of claims 1 to 3, wherein the temperature value measured in the measurement step is also used for correcting the ORP value in the calculation control step. It is a control device of the residual chlorine removal system provided in the residual chlorine removal system that reduces the water to be treated containing residual chlorine.
The residual chlorine removal system includes a reaction tank for introducing water to be treated containing residual chlorine, and a reducing agent supply unit for supplying a reducing agent containing sulfite ion or hydrogen sulfite ion to the reaction tank.
The control device includes a measuring unit for measuring the redox potential (ORP) and pH of the water to be treated in the reaction vessel.
It is provided with an arithmetic control unit that corrects the measured ORP value using the pH value measured by the measuring unit and adjusts the supply amount of the reducing agent by the reducing agent supply unit based on the corrected ORP value. A control device for the characteristic residual chlorine removal system. The correction of the ORP value in the arithmetic control unit uses the acid dissociation constant of the reducing agent for the one in which the valence of the reducing agent changes with the change in pH when the reducing agent is supplied, and the coefficient in the Nernst equation. The control device for the residual chlorine removal system according to claim 5, wherein the method is performed based on a correction formula obtained by changing the above. The control device for the residual chlorine removal system according to claim 5 or 6, wherein the correction of the ORP value in the arithmetic control unit is performed based on the correction formula represented by the following formula.

_{E C = E M -2.3026 (RT} / z A F) (pH 0 -pH A)
Here, z _A = (2 × 10 ^(pHA-7.2) +1) / (10 ^(pHA-7.2) +1) …… (formula)

Also, _{E C} is corrected ORP value (correction ORP value), _{E M} is the measured ORP value (ORP measured value), pH value before pH ₀ is adding a reducing agent, a pH value pH _A is to be measured Shown. Further, R is the molar gas constant (= 8.314 J / K · mol), F is the Faraday constant (= 96485 C / mol), z _A is the average ionic valence, and T is the absolute temperature (unit: K). .. In addition to measuring the temperature of the water to be treated in the reaction vessel in the measuring unit,
The control device for the residual chlorine removal system according to any one of claims 5 to 7, wherein the temperature value measured by the measuring unit is also used for correcting the ORP value in the arithmetic control unit. A residual chlorine removal system that reduces the water to be treated containing residual chlorine.
A reaction tank that introduces water to be treated containing residual chlorine,
A reducing agent supply unit that supplies a reducing agent containing sulfite ions or hydrogen sulfite ions to the reaction vessel,
A system for removing residual chlorine, which comprises the control device according to any one of claims 5 to 8.