JP7284624B2 - Residual chlorine removal method, controller for residual chlorine removal system, and residual chlorine removal system - Google Patents

Description

The present invention relates to a method for removing residual chlorine, a control device for a system for removing residual chlorine, and a system for removing residual chlorine. The present invention also relates to a residual chlorine removing method, a control device for a residual chlorine removing system, and a residual chlorine removing system, in which reduction treatment is performed using a reducing agent.

Chlorine agents are used as bacterial growth inhibitors and sterilizing agents in water treatment facilities, or as oxidizing agents in odor treatment. At this time, in order to avoid a shortage of the chlorine agent in the water to be treated, it is necessary to supply an excess of the chlorine agent. The water to be treated containing excessive residual chlorine cannot be discharged into public water areas because of the risk of adverse effects and harm to humans and organisms. 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, a method using an adsorbent such as activated carbon is known, but there are problems such as difficulty in determining performance deterioration of the adsorbent and high cost.
Another known method for removing residual chlorine is chemical removal by supplying a reducing agent to the residual chlorine.

For example, Patent Literature 1 describes a method for controlling the concentration of residual chlorine in a method for removing chlorine in which a reducing agent is supplied to water containing chlorine. In addition, in Patent Document 1, the oxidation-reduction potential (hereinafter referred to as "ORP") of water containing chlorine to which a reducing agent is supplied is measured, and the measured value of the measured ORP and its change are used to supply the reducing agent. It states that the situation is determined.

Japanese Patent Application Laid-Open No. 2004-33800

When the residual chlorine is removed by supplying the reducing agent to the residual chlorine, if the reducing agent is excessively supplied with respect to the residual chlorine, the reducing agent will remain. In this case, there is a problem that the components of the reducing agent cannot be discharged into public waters, so it is necessary to appropriately control the supply amount of the reducing agent for residual chlorine.

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

On the other hand, the present inventors found that when a reducing agent is supplied to water to be treated containing residual chlorine, the pH of the water to be treated may change due to the effect of the reducing agent. It was found that the amount of supply of the reducing agent could not be controlled correctly because it was not linked to the supply situation.

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

In particular, when a reducing agent containing sulfite ions or hydrogen sulfite ions 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 for residual chlorine by measuring the ORP, it is necessary to consider the dissociation state of the reducing agent due to pH fluctuations.

An object of the present invention is to remove residual chlorine by supplying a reducing agent to water to be treated containing residual chlorine. An object of the present invention is to provide a method for removing chlorine, a control device for a system for removing residual chlorine, and a system for removing residual chlorine.

As a result of intensive studies on the above problems, the present inventors measured ORP and pH in removing residual chlorine by supplying a reducing agent to the water to be treated containing residual chlorine, and used the measured value of pH as one of the parameters. By correcting the ORP value, the inventors have found that the influence of the pH fluctuation on the ORP value can be eliminated, and the amount of the reducing agent supplied can be appropriately controlled by the ORP measurement, thus completing the present invention.
That is, the present invention is the following residual chlorine removing method, controller for residual chlorine removing system, and residual chlorine removing system.

The method for removing residual chlorine of the present invention for solving the above-mentioned problems is a method for removing residual chlorine in which water to be treated containing residual chlorine is subjected to reduction treatment , wherein the water to be treated containing residual chlorine is added with a reduction treatment step of supplying a reducing agent that generates sulfate ions; a measurement step of measuring the oxidation-reduction potential (ORP) and pH of the water to be treated after the reduction treatment step; and using the pH value measured in the measurement step. and an arithmetic control step of correcting the ORP value measured by the method and adjusting the supply amount of the reducing agent in the reduction process based on the corrected ORP value.
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 calculation control step based on the measurement results, thereby obtaining a corrected ORP value that takes into account the influence of pH. be able to. Furthermore, the calculation control step makes it possible to appropriately grasp the timing for controlling the supply amount of the reducing agent, and to appropriately control the supply amount of the reducing agent. As a result, in removing residual chlorine, it is possible to suppress the excessive supply of the reducing agent to 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 in the case where the valence of the reducing agent changes with the change in pH during the reduction treatment step. The acid dissociation constant is used, and the correction is performed based on a correction formula in which the coefficient in the Nernst formula is changed.
According to this feature, it is possible to correct the ORP value even for a reducing agent having different valences depending on the dissociated state of the reducing agent depending on the pH, such as a reducing agent containing sulfite ions or hydrogen sulfite ions. This makes it possible to improve the accuracy of correction of the ORP value.

Further, one embodiment of the residual chlorine removing method of the present invention is characterized in that 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)
In addition, _EC is the corrected ORP value (corrected ORP value), _EM is the measured ORP value (ORP actual value), pH ₀ is the pH value before adding the reducing agent, and pH _A is the measured pH value. showing. Furthermore, R is the molar gas constant (= 8.314 J/K mol), F is the Faraday constant (= 96485 C/mol), z _A is the average ion valence, and T is the absolute temperature (unit: K). .
According to this feature, even for a reducing agent containing sulfite ions or hydrogen sulfite ions, in which the valence of the dissociation state of the reducing agent differs depending on the pH, continuous calculation can be performed without changing the correction formula. It is possible to do As a result, it is possible to simplify the arithmetic processing for correcting the ORP value and increase the processing speed of the arithmetic processing.

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

Further, the control device for the residual chlorine removal system of the present invention for solving the above-mentioned problems is a control device for the residual chlorine removal system provided in the residual chlorine removal system for reduction treatment of 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 that generates sulfate ions after reacting with the residual chlorine to the reaction tank, The control device includes a measuring unit for measuring the oxidation-reduction potential (ORP) and pH of the water to be treated in the reaction tank, and using the pH value measured by the measuring unit, corrects the measured ORP value, and corrects the ORP value. and an arithmetic control unit that adjusts the amount of the reducing agent supplied by the reducing agent addition unit based on the above.
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 results, thereby improving the ORP considering the influence of pH. A correction value can be obtained. Furthermore, the arithmetic control unit can appropriately grasp the timing for controlling the supply amount of the reducing agent, and can appropriately control the supply amount of the reducing agent. As a result, in removing residual chlorine, it is possible to suppress the excessive supply of the reducing agent to the residual chlorine.

Further, as one embodiment of the control device for the residual chlorine removal system of the present invention, the correction of the ORP value in the arithmetic control unit is performed by changing the valence of the reducing agent as the pH changes when the reducing agent is added. It is characterized by using the acid dissociation constant of the reducing agent and performing it based on a correction equation in which the coefficient in the Nernst equation is changed.
According to this feature, it is possible to correct the ORP value even for a reducing agent having different valences depending on the dissociated state of the reducing agent depending on the pH, such as a reducing agent containing sulfite ions or hydrogen sulfite ions. This makes it possible to improve the accuracy of correction of the ORP value.

Further, one embodiment of the controller for 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)
In addition, _EC is the corrected ORP value (corrected ORP value), _EM is the measured ORP value (ORP actual value), pH ₀ is the pH value before adding the reducing agent, and pH _A is the measured pH value. showing. Furthermore, R is the molar gas constant (= 8.314 J/K mol), F is the Faraday constant (= 96485 C/mol), z _A is the average ion valence, and T is the absolute temperature (unit: K). .
According to this feature, even for a reducing agent containing sulfite ions or hydrogen sulfite ions, in which the valence of the dissociation state of the reducing agent differs depending on the pH, continuous calculation can be performed without changing the correction formula. It is possible to do As a result, it is possible to simplify the arithmetic processing for correcting the ORP value and increase the processing speed of the arithmetic processing.

Further, as one embodiment of the control device for 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 tank, and the ORP value correction in the arithmetic control unit It is characterized in that it also uses the temperature value measured by the measuring unit.
According to this feature, the ORP value can be corrected using the temperature of the water to be treated as a parameter. This makes it possible to improve the accuracy of correction of the ORP value.

Further, as a residual chlorine removal system of the present invention for solving the above problems, there is provided a residual chlorine removal system for reduction treatment of water to be treated containing residual chlorine, which is a reaction tank into which water to be treated containing residual chlorine is introduced. and a reducing agent supply unit for supplying a reducing agent that generates sulfate ions after reacting with residual chlorine to the reaction tank, and any one of the control devices described above.
The residual chlorine removal system of the present invention measures the ORP and pH of the reaction tank, and based on the measurement results, corrects the ORP value with the control device, thereby obtaining a correction value of ORP considering the influence of pH. can be done. Furthermore, the arithmetic control unit of the control device can appropriately grasp the timing for controlling the supply amount of the reducing agent, and can appropriately control the supply amount of the reducing agent. As a result, in removing residual chlorine, it is possible to suppress the excessive supply of the reducing agent to the residual chlorine.

According to the present invention, in removing residual chlorine by supplying a reducing agent to water to be treated containing residual chlorine, it is possible to appropriately control the amount of supply of the reducing agent by ORP measurement, taking into account the influence of changes in pH. A method for removing chlorine, a control device for a system for removing residual chlorine, and a system for removing residual chlorine can be provided.

1 is a schematic explanatory diagram of a residual chlorine removal system in a first embodiment of the present invention; FIG. FIG. 4 is a schematic diagram showing changes over time of pH _A , the ORP actual measurement value before correction, and the corrected ORP value after correction in the first embodiment of the present invention. FIG. 4 is a schematic diagram showing temporal changes in the corrected ORP value related to the method for removing residual chlorine in the first embodiment of the present invention. FIG. 4 is a schematic explanatory diagram of a residual chlorine removal system in a second embodiment of the present invention;

INDUSTRIAL APPLICABILITY The method for removing residual chlorine, the control device for the system for removing residual chlorine, and the system for removing residual chlorine according to 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 treatment in the present invention, is not particularly limited as long as it contains residual chlorine. The water to be treated may be wastewater discharged from various factories, treatment plants, or the like, or may be circulating water used in plants or the like. In addition to industrial water, water that is sterilized and sterilized with a chlorine agent, such as river water, tap water, and water stored in tanks such as pools and public baths. Here, residual chlorine refers to a chlorine compound that effectively acts on sterilization, sterilization, and oxidation reaction of substances contained in water. Moreover, from the viewpoint of exhibiting the effect of the present invention more, it is preferable that the water to be treated, which is the target of the treatment of the present invention, mainly contains free chlorine as residual chlorine. Here, free chlorine refers to residual chlorine present in water as chlorine gas, hypochlorous acid, and hypochlorite ions. Such water to be treated includes water to be treated using sodium hypochlorite as a chlorine agent. The water to be treated, which is the object of treatment 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 can be treated by the present invention.

EMBODIMENT OF THE INVENTION Hereafter, the residual chlorine removal method, the control apparatus of a residual chlorine removal system, and the residual chlorine removal system which concern on this invention are demonstrated in detail, referring drawings. It should be noted that the contents described in the following embodiments are merely examples for explaining the residual chlorine removing method, the residual chlorine removing system control device, and the residual chlorine removing system according to the present invention, and are limited thereto. not a thing

[First embodiment]
(Residual chlorine removal system)
FIG. 1 is a schematic illustration of the residual chlorine removing system of 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 to be treated W containing residual chlorine, a reducing agent supply unit 3 for supplying a reducing agent R, and an ORP measuring unit. 4 , a pH measurement unit 5 and an arithmetic control unit 6 . Further, a line L1, which is an introduction pipe for introducing the water W to be treated 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. have. Note that the dashed-dotted arrows in FIG. 1 indicate that they are connected for input or control.

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 to be treated W is supplied to the reaction tank 2 through a line L1 provided in the reaction tank 2. As shown in FIG. A reducing agent R is supplied to the reaction tank 2 from a reducing agent supply unit 3 to be described later, and residual chlorine in the water W to be treated is reduced. The treated water W1 after the reduction treatment is discharged from the reaction tank 2 through a line L2 provided in the reaction tank 2. As shown in FIG. In addition, the reaction vessel 2 may be provided with a stirrer 21 therein. Thereby, the reaction between the water to be treated W and the reducing agent R can be promoted.

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 that stores the reducing agent R, a reducing agent supply line 32 that supplies the reducing agent R to the reaction tank 2, and a supply amount of the reducing agent R. is provided with a reducing agent supply amount control unit 33 for controlling the

The reducing agent storage tank 31 is not particularly limited as long as the reducing agent R can be stored. For example, any tank that can stably store the solid or liquid reducing agent R may be used, and examples thereof include a shielded cylindrical tank and a rectangular parallelepiped tank. Moreover, 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 ions or hydrogen sulfite ions. More specific examples include sodium thiosulfate, sodium sulfite and sodium hydrogensulfite. By using these as reducing agents R, harmless sulfate ions can be generated after reaction with residual chlorine. In addition, since substances containing sulfite ions or hydrogen sulfite ions have a strong reducing power, by using these as the reducing agent R, the reaction time with residual chlorine in the water W to be treated can be shortened, and residual chlorine can be reduced. Removal can proceed in a short time.
The reducing agent R may be supplied to the water W to be treated in the reaction tank 2 as a solid, but the stability of the reducing agent R and the reaction rate with residual chlorine in the water W to be treated are determined. In view of this, the reducing agent R is preferably stored in the reducing agent storage tank 31 as an aqueous solution and supplied to the water W to be treated 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 .
The reducing agent supply amount control unit 33 is provided on the reducing agent supply line 32 to control the supply amount of the reducing agent R based on an input from the arithmetic control unit 6 described later.

When the reducing agent R is a solution, the reducing agent supply amount control unit 33 may be a pump, a flow control valve, or the like for controlling the flow rate in the reducing agent supply line 32 . At this time, the control of the flow rate in the reducing agent supply amount control unit 33 is performed by repeatedly executing supply and stop of supply of the reducing agent R by on/off control of the pump, control of the rotation speed of the pump by the inverter, and transfer by the pump. For example, the amount of supply of the reducing agent R is changed continuously or non-continuously by controlling the amount of volume or by controlling the degree of opening/closing of the flow control valve.
Further, when the reducing agent R is 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 performed by repeatedly supplying and stopping the supply of the reducing agent R by controlling the opening and closing of the valve and the supply hopper, and by opening and closing the valve and the supply hopper. For example, the amount of supply of the reducing agent R is changed continuously or non-continuously by controlling the degree of reduction.

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

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

The pH measuring unit 5 measures the pH value of the water W to be treated in the reaction tank 2 . The pH measurement unit 5 is also connected to the calculation control unit 6 so as to be inputtable, and the pH value data obtained by the pH measurement unit 5 is inputted to the calculation control unit 6 .

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

The calculation control section 6 controls the reducing agent supply amount control section 33 based on the measurement data from the ORP measurement section 4 and the pH measurement section 5 .
The calculation control section 6 includes a calculation section 61 and a control section 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 temporal change in the obtained corrected ORP value. to determine the timing of
For example, the calculation unit 61 may be provided with calculation means for calculating the amount of change in the ORP value due to the pH value and the ORP value after correction based on a formula (correction formula) necessary for correcting the ORP value. The configuration is not particularly limited. Specific examples of the computing unit 61 include a computer including a CPU, ROM, RAM, HDD, etc., and a sequencer (PLC (Programmable Logic Controller)).

ここで、［Ｈ_０］はｐＨ変化前（還元剤を添加する前）の水素イオン濃度（単位：ｍｏｌ／Ｌ）であり、ｐＨ_０（＝－ｌｎ［Ｈ_０］）はこのときのｐＨ値を示している。また、［Ｈ_Ａ］はｐＨ変化後（還元剤を添加した後）に実測される水素イオン濃度（単位：ｍｏｌ／Ｌ）であり、ｐＨ_Ａ（＝－ｌｎ［Ｈ_Ａ］）はこのときのｐＨ値を示している。さらに、Ｒはモル気体定数（＝８．３１４Ｊ／Ｋ・ｍｏｌ）、Ｆはファラデー定数（＝９６４８５Ｃ／ｍｏｌ）、ｚはイオン価数、Ｔは絶対温度（単位：Ｋ）を示している。
したがって、式１に基づきΔＥを求めた後、実測されるＯＲＰの値（以下、「ＯＲＰ実測値（Ｅ_Ｍ）」という。）からΔＥを減算することで、補正されたＯＲＰの値（以下、「補正ＯＲＰ値（Ｅ_Ｃ）」という。）を求めることができる（式２）。

A 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, [H _A ] is the hydrogen ion concentration (unit: mol/L) actually measured after the pH change (after adding the reducing agent), and pH _A (=−ln[H _A ]) is the value at this time. pH values are indicated. Furthermore, R is the molar gas constant (=8.314 J/K·mol), F is the Faraday constant (=96485 C/mol), z is the ionic valence, and T is the absolute temperature (unit: K).
Therefore, after obtaining ΔE based on Equation 1, the corrected ORP value ( _hereinafter referred to as referred to as “corrected ORP value (E _C )”) can be obtained (equation 2).

ここで、式３における酸解離定数Ｋ_ａ１は１．４×１０^－２（ｍｏｌ／Ｌ）、式４における酸解離定数Ｋ_ａ２は６．５×１０^－８（ｍｏｌ／Ｌ）とする。
このとき、亜硫酸は、ｐＨ＜１．９（＝ｐＫ_ａ１）ではＳＯ_２として、１．９＜ｐＨ＜７．２（＝ｐＫ_ａ２）ではＨＳＯ_３ ^-として、さらにｐＨ＞７．２ではＳＯ_３ ^２-として存在する比率が高まることを意味している。なお、二酸化硫黄（ＳＯ_２）として存在する比率が高いｐＨでは、ＳＯ_２が気化するため還元剤Ｒとしては利用できない。したがって、本実施例においては、ｐＨが少なくとも１．９以上の範囲にある場合のＯＲＰ値の補正について説明する。 On the other hand, the ionic valence z in Formula 1 described above may change depending on the pH.
For example, sulfurous acid ₍ ^H ₂ SO ₃ ) has different dissociation _{states in} water depending on the pH ^{. −} ) (equations 3 and 4).

Here, the acid dissociation constant K _a1 in Equation 3 is 1.4×10 ⁻² (mol/L), and the acid dissociation constant K _a2 in Equation 4 is 6.5×10 ⁻⁸ (mol/L).
At this time, sulfurous acid is converted to SO ₂ at pH<1.9 (=pK _a1 ), HSO ₃ ⁻ at 1.9<pH<7.2 (=pK _a2 ), and SO ₃ at pH>7.2. It means that the ratio of existing as ^2- increases. At a pH where the ratio of sulfur dioxide (SO ₂ ) present is high, it cannot be used as the reducing agent R because SO ₂ evaporates. Therefore, in this embodiment, correction of the ORP value when the pH is at least in the range of 1.9 or higher will be described.

When the liquid to be treated W is alkaline, if reduction treatment is performed using acidic sodium sulfite as the reducing agent R, the pH of the water to be treated W decreases as the reduction treatment progresses, and may pass through pH 7.2. At this time, as shown in Equation 4, sulfite ions (SO ₃ ²⁻ ) change to hydrogen sulfite ions (HSO ₃ ⁻ ), and the ion valence z in Equation 1 changes from 2 to 1.

In addition, regarding sulfur dioxide (SO ₂ ), hydrogen sulfite ion (HSO ₃ ⁻ ), and sulfite ion (SO ₃ ²⁻ ) generated by dissociation of sulfurous acid, since the total amount of each substance is constant, sulfite ion ( SO ₃ ²⁻ ) and hydrogen sulfite ions (HSO ₃ ⁻ ) (substance amount ratio) change gradually around pH 7.2.
Therefore, the ionic valence z was averaged in order to perform continuous calculation in the pH region where the ionic valence z changes.

このとき、二酸化硫黄（ＳＯ_２）は系内にほぼ存在しないとみなすことができる。したがって、α＋β＝１が成り立っている。 First, regarding the substance amount ratio of sulfite ion (SO ₃ ²⁻ ) and hydrogen sulfite ion (HSO ₃ ⁻ ) at a certain pH value (pH _X ), the substance amount ratio of sulfite ion (SO ₃ ²⁻ ) is α, hydrogen sulfite When the substance amount ratio of ions (HSO ₃ ⁻ ) is β, the following formulas 5 and 6 are obtained.

At this time, it can be considered that almost no sulfur dioxide (SO ₂ ) exists in the system. Therefore, α+β=1 holds.

Assuming that the ion valence z is determined by the substance amount ratio described above, the average ion valence z _A is given by the following equation 7.

なお、式８中のｚ_Ａ以外のその他の定数、変数については、式１と同じである。 A value obtained by substituting z _A shown in Equation 7 as the ion valence z in Equation 1 is used as a correction equation (Equation 8) for obtaining a corrected ORP value (E _C ).

Note that constants and variables other than _zA in Equation 8 are the same as in Equation 1.

The calculation unit 61 calculates the corrected ORP value (E _C ) from the actually measured pH value (pH _A ) and the ORP actual measurement value (E _M ) using Equation 8. At this time, by using Equation 8, continuous arithmetic processing can be performed without changing the correction equation even if the valence of the dissociation state of the reducing agent R differs depending on the pH.
Further, the calculation unit 61 determines the timing of supplying or stopping the supply of the reducing agent R based on the temporal change of the calculated corrected ORP value (E _C ). Then, the determination result is input to the control section 62 .

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

The control unit 62 receives a determination regarding the supply or stop of the supply of the reducing agent R from the calculation unit 61, and controls the reducing agent supply amount control unit 33 according to the result of this determination to supply or stop the supply of the reducing agent R. conduct.
As 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 section 33 is 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 diagram 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 system 1a for removing residual chlorine of this embodiment. In FIG. 2, the horizontal axis indicates the passage of time, the left vertical axis indicates the ORP value, and the right vertical axis indicates the pH value. 2 indicates the ORP actual measurement value (E _M ) before correction, and the solid line indicates the corrected ORP value (E _C ) after correction by Equation (8). The thick line in FIG. 2 indicates the actually measured pH value (pH _A ).

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

However, as shown in FIG. 2, the measured ORP value (E _M ) before correction is affected by pH _fluctuations . value increases. In particular, when the concentration of residual chlorine is high and the amount of supply of reducing agent R is large, the variation in pH is also large, so the influence of pH _A on the measured ORP value (E _M ) before correction is large. Therefore, even if the ORP actual measurement value (E _M ) before correction is used, it is not possible to appropriately grasp the timing at which the supply of the reducing agent R should be stopped in removing the residual chlorine.

On the other hand, as shown in FIG. 2, the corrected ORP value (E _C ) after correction is not affected by pH fluctuations, and after a certain period of time (time B in FIG. 2) from the supply of the reducing agent R, the ORP 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 W to be treated, 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 result of the determination is input to the control unit 62, so that excessive supply of the reducing agent R can be suppressed. .
Therefore, by correcting the ORP actual measurement value using the equation 8 in the calculation unit 61, it is possible to obtain a corrected ORP value considering the influence of pH. As a result, the calculation unit 61 can appropriately grasp the timing for 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 configurations relating to the ORP measuring section 4, the pH measuring section 5, and the arithmetic control section 6 in this embodiment can be made independent as a control device according to the present invention. This controller can be applied to existing residual chlorine removal systems. As a result, the residual chlorine removal system and residual chlorine removal method of the present invention can be provided in an existing residual chlorine removal system by a simple installation work.

(Method for removing residual chlorine)
A method for removing residual chlorine using the system for removing residual chlorine in this embodiment will be described. Although the residual chlorine removing system is described based on the structure shown in FIG. 1, it is not limited to this.

FIG. 3 is a schematic diagram showing changes over time in the corrected ORP value (E _C ) after correction. The horizontal axis indicates the passage of time, and the vertical axis indicates the ORP value. FIG. 3 also shows the time points at which the reducing agent supply amount control unit 33 supplies and stops the supply of the reducing agent R. As shown in FIG.

First, the reducing agent supply unit 3 supplies the reducing agent R to the water to be treated W containing residual chlorine in the reaction tank 2 (time A in FIG. 3). At this time, the reaction between the residual chlorine and the reducing agent R proceeds (reduction treatment step). Also, the ORP and pH in the reaction tank 2 are measured by the ORP measuring section 4 and the pH measuring section 5, respectively (measurement step). At this time, the calculation unit 61 in the calculation control unit 6 performs correction based on Equation 8 using the ORP actual value (E _M ) and the actually measured pH value (pH _A ) to calculate the corrected ORP value (E _C ). (calculation control step-1).

As the reduction treatment step progresses, the residual chlorine and reducing agent R in the water W to be treated decrease, and the required amount of reducing agent R is supplied to the residual chlorine. 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. Therefore, the calculation unit 61 determines to stop the reduction process when the corrected ORP value (E _C ) decreases and reaches the preset lower limit of the ORP value (E _LS ). Then, based on this determination result, the control unit 62 controls the reducing agent supply amount control unit 33 to stop the supply of the reducing agent R (arithmetic control step-2). At this time, it is preferable that the time point (time C in FIG. 3) at which the supply of the reducing agent R is stopped has a small interval from the time B at which the reduction process is completed. As a result, excessive supply of the reducing agent R can be suppressed.

In addition, since the water to be treated W containing residual chlorine is continuously supplied to the reaction tank 2, the corrected ORP value (E _C ) (and the measured ORP value (E _M )) in the reaction tank 2 is again Rise. When the re-increased corrected ORP value (E _C ) reaches the preset upper limit standard value (E _HS ) of the ORP value or the corrected ORP value before decrease (E _C ), the calculation unit 61 starts the reduction process. Make a decision to restart. Then, based on the determination result, the controller 62 controls the reducing agent supply amount controller 33 to restart the supply of the reducing agent R at time D in FIG. 3 (arithmetic 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 becomes possible.

As described above, by using the method for removing residual chlorine, the system for removing residual chlorine, and the control device thereof according to the present embodiment, it is possible to grasp the fluctuation of the ORP value considering the influence of pH, and the amount of the reducing agent in the reduction treatment. It is possible to appropriately control the amount of supply. As a result, excessive supply of the reducing agent can be suppressed in removing residual chlorine by reduction treatment.

[Second embodiment]
FIG. 4 is a schematic illustration of the residual chlorine removing system 1b of the second embodiment of the present invention.
As shown in FIG. 4, the residual chlorine removing system 1b according to the present embodiment is obtained by adding a temperature measuring section 7 to the residual chlorine removing system 1a of the first embodiment. Also, the temperature measurement unit 7 is connected to the arithmetic control unit 6 so as to be inputtable.
Note that, of the configuration of the residual chlorine removing system 1b in this embodiment, the description of the same configuration as that of the residual chlorine removing system 1a of the first embodiment will be omitted.

The residual chlorine removal system 1b of this embodiment measures the temperature in the reaction vessel 2 by the temperature measurement unit 7, and based on the measurement result, the calculation control unit 6 calculates the corrected ORP value (E _C ) and the corrected ORP It controls 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 it can measure the temperature of the water W to be treated in the reaction tank 2 . A known thermometer can be used. For example, the temperature measurement unit 7 may have a detection part provided in water, or may measure the temperature of the water surface. Note that the temperature measuring unit 7 is not limited to this, and may be any unit that can stably measure the temperature of the water W to be treated. Temperature data obtained by the temperature measurement unit 7 is input to the arithmetic control unit 6 .

In the calculation unit 61 of the calculation control unit 6, when the temperature in the reaction vessel 2 is stable, such as when the temperature obtained by the temperature measurement unit 7 is within a certain range, the absolute temperature T can be treated as a constant.
On the other hand, when the temperature of the water W to be treated in the reaction tank 2 is not stable, such as when the temperature obtained by the temperature measurement unit 7 fluctuates, the absolute temperature T in Equation 8 is used as a variable, and the temperature obtained by the temperature measurement unit 7 is shall be input and the ORP actual measurement value (E _M ) shall be corrected. This makes it possible to determine the corrected ORP value (E _C ) using calculations that consider the influence of temperature fluctuations.

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

Moreover, residual chlorine can be removed by using the residual chlorine removing system 1b of the present embodiment 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 reducing agent supplied in the residual chlorine treatment method in which reduction treatment is performed using a reducing agent.

Furthermore, the configuration obtained by adding the temperature measurement unit 7 to the ORP measurement unit 4, the pH measurement unit 5 and the arithmetic control unit 6 in this embodiment can be made independent as a control device according to the present invention. This controller can be applied to existing residual chlorine removal systems. As a result, the residual chlorine removal system and residual chlorine removal method of the present invention can be provided in an existing residual chlorine removal system by a simple installation work.

The embodiment described above is an example of the method for removing residual chlorine, the system for removing residual chlorine, and the control device thereof. The method for removing residual chlorine, the system for removing residual chlorine, and the control device thereof according to the present invention are not limited to the above-described embodiments, and the residual chlorine according to the above-described embodiments is within the scope of not changing the gist of the claims. The removal method, residual chlorine removal system, and controller thereof may be modified.

For example, in the present embodiment, the reducing agent containing sulfite ions or hydrogen sulfite ions was described, but the present invention is not limited to this. For example, when the valence of the reducing agent present in the water W to be treated changes when the pH fluctuates in the reduction treatment, a correction formula based on the Nernst equation is used using the formula relating to the average ion valence. can be calculated|required, and the residual chlorine removal method of this embodiment, a residual chlorine removal system, and its control apparatus can be used suitably.

Further, in this embodiment, the water to be treated W containing residual chlorine to be treated is alkaline, the reducing agent is acidic, and the pH of the water to be treated W changes from the alkaline side to the acidic side. Although processing has been described, it is not limited to this. The method for removing residual chlorine and the system for removing residual chlorine of the present embodiment are also applicable 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.

INDUSTRIAL APPLICABILITY The method for removing residual chlorine, the system for removing residual chlorine, and the controller thereof according to the present invention are used for reduction treatment of water to be treated containing residual chlorine. In particular, the method for removing residual chlorine, the system for removing residual chlorine, and the control device thereof according to the present invention are suitably used for reduction treatment using a reducing agent whose dissociation state in the water to be treated changes depending on the 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 6 calculation control unit 61 calculation unit 62 control unit 7 temperature measurement unit L1, L2 lines E _C correction ORP value E _M ORP actual measurement value E _HS ORP upper limit reference value E _LS ORP lower limit Reference value, R reducing agent, W water to be treated, W1 treated water

Claims (9)

A residual chlorine removal method for reducing treatment of water to be treated containing residual chlorine,
a reduction treatment step of supplying , to the water to be treated containing residual chlorine, a reducing agent that generates sulfate ions after reacting with the residual chlorine ;
a measuring step of measuring the oxidation-reduction potential (ORP) and pH of the water to be treated after the reduction treatment step;
A corrected ORP value is calculated based on the Nernst equation from the oxidation-reduction potential (ORP) and pH values measured in the measurement step, and the supply amount of the reducing agent in the reduction treatment is adjusted based on the calculated corrected ORP value. A method for removing residual chlorine, comprising: The correction of the ORP value in the calculation control step uses the acid dissociation constant of the reducing agent and changes the coefficient in the Nernst equation for those in which the valence of the reducing agent changes with the change in pH during the reduction treatment step. 2. The method for removing residual chlorine according to claim 1, wherein the residual chlorine removal method is performed based on a correction formula obtained by 3. The residual chlorine removing method according to claim 1, wherein the correction of the ORP value in said arithmetic control step is performed based on a 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)

In addition, _EC is the corrected ORP value (corrected ORP value), _EM is the measured ORP value (ORP actual value), pH ₀ is the pH value before adding the reducing agent, and pH _A is the measured pH value. showing. Furthermore, R is the molar gas constant (= 8.314 J/K mol), F is the Faraday constant (= 96485 C/mol), z _A is the average ion valence, and T is the absolute temperature (unit: K). . In the measuring step, further measuring the temperature of the water to be treated after the reduction treatment step,
The method for removing residual chlorine according to any one of claims 1 to 3, wherein the temperature value measured in said measuring step is also used for correcting the ORP value in said arithmetic control step. A control device for a residual chlorine removal system provided in a residual chlorine removal system for reduction treatment of 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 that generates sulfate ions after reaction with the residual chlorine to the reaction tank. prepared,
The control device includes a measurement unit that measures the oxidation-reduction potential (ORP) and pH of the water to be treated in the reaction tank;
A corrected ORP value is calculated based on the Nernst equation from the oxidation-reduction potential (ORP) and pH values measured by the measurement unit, and the amount of the reducing agent supplied by the reducing agent supply unit based on the calculated corrected ORP value. A control device for a residual chlorine removal system, comprising: an arithmetic control unit that adjusts the Correction of the ORP value in the arithmetic control unit uses the acid dissociation constant of the reducing agent for the valence of the reducing agent that changes with the change in pH when the reducing agent is supplied, and the coefficient in the Nernst equation 6. The control device of the residual chlorine removing system according to claim 5, wherein the correction is performed based on the correction formula in which is changed. 7. The control device of the residual chlorine removal system according to claim 5, wherein the correction of the ORP value in said arithmetic control unit is performed based on a 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)

In addition, _EC is the corrected ORP value (corrected ORP value), _EM is the measured ORP value (ORP actual value), pH ₀ is the pH value before adding the reducing agent, and pH _A is the measured pH value. showing. Furthermore, R is the molar gas constant (= 8.314 J/K mol), F is the Faraday constant (= 96485 C/mol), z _A is the average ion valence, and T is the absolute temperature (unit: K). . Further measuring the temperature of the water to be treated in the reaction tank in the measurement unit,
8. The controller for a residual chlorine removal system according to claim 5, wherein the temperature value measured by said measuring unit is also used for correcting the ORP value in said arithmetic control unit. A residual chlorine removal system for reduction treatment of water to be treated containing residual chlorine,
a reaction tank into which water to be treated containing residual chlorine is introduced;
a reducing agent supply unit that supplies a reducing agent that generates sulfate ions after reacting with residual chlorine to the reaction tank;
A residual chlorine removing system comprising a control device according to any one of claims 5 to 8.

Images