JP6766004B2 - Electrocorrosion protection system and seawater desalination plant equipped with it - Google Patents

Description

The present invention relates to an electrocorrosion protection system and a plant equipped with the same, and more particularly to an external power supply type electrocorrosion protection system and a plant equipped with the same.

The technique described in Patent Document 1 is known as a technique for preventing corrosion of a metal surface immersed in an electrolytic solution such as seawater. In Patent Document 1, between the flow path portion (pipe, pump) of a fluid (seawater) formed of metal and the anode that contacts the fluid flowing through the flow path section while being electrically insulated from the flow path section. This is an electric anticorrosion method in which an anticorrosion voltage is applied to an anticorrosion voltage and an anticorrosion current is circulated through a distribution path so that the anticorrosion current becomes a predetermined current value or potential when the anticorrosion current falls below a predetermined current value or potential. A configuration that increases the anticorrosion voltage is described. Further, Patent Document 1 discloses that when the anticorrosion voltage exceeds the upper limit voltage, a voltage in the direction opposite to the anticorrosion voltage is applied to the anode or the anode.

Japanese Unexamined Patent Publication No. 2016-17189

However, in the technique described in Patent Document 1, hypochlorous acid generated by increasing the anticorrosion voltage is not considered at all. Hypochlorite causes deterioration of the RO membrane (Reverse Osmosis Membrane: reverse osmosis membrane) in the RO membrane joule that constitutes a seawater desalination plant.

Therefore, the present invention provides an electrocorrosion protection system capable of suitably removing hypochlorous acid even when an anticorrosion voltage of a predetermined value or more is applied, and a seawater desalination plant provided with the same.

In order to solve the above problems, in the electrolytic corrosion protection system according to the present invention, at least an electrode arranged via an insulating material in a pipe made of a metal material through which an electrolytic solution flows, and a pipe made of the electrode and the metal material An anticorrosion power supply that applies a voltage between the two, and at least a flow meter that measures the flow rate of the electrolytic solution that is installed in the pipe made of the metal material and that flows through the pipe, and the following in the electrolytic solution that flows through the pipe. It is equipped with a residual salt meter that measures the chloric acid concentration, and the inside of the pipe is filled with the measured value of the flow rate of the electrolytic solution by the flow meter and the measured value of the hypochlorous acid concentration in the electrolytic solution by the residual salt meter. It is characterized by having a control unit that controls the addition of at least a hypochlorous acid removing agent to the flowing electrolytic solution.
Further, the seawater desalination plant according to the present invention introduces a pressurizing pump that pressurizes the seawater treated by the pretreatment section and seawater pressurized by the pressurizing pump, and is concentrated water that is a high-concentration salt water. An energy recovery device that introduces a reverse osmosis membrane module that separates the water from the reverse osmosis membrane module and the concentrated water discharged from the reverse osmosis membrane module and recovers energy as a part of the power for driving the pressurizing pump. A pipe connecting the pressurizing pump and the reverse osmosis membrane module to allow pressurized seawater to flow, a pipe connecting the reverse osmosis membrane module to the energy recovery device to allow concentrated water to flow, and the addition. An electrode arranged via an insulating material in a pipe through which the compressed seawater flows and / or a pipe through which the concentrated water flows, and a pipe through which the electrode and the pressurized seawater flow and / or the above. An anticorrosion power supply that applies a voltage between the pipe through which the concentrated water flows, a pipe through which pressurized seawater flows, and / or a pump installed in the pipe through which the concentrated water flows, and a pump that flows through the pipe. An anticorrosion system comprising a flow meter for measuring the flow rate of pressurized seawater and / or concentrated water and a residual salt meter for measuring the concentration of hypochlorite in pressurized seawater and / or concentrated water. The electrocorrosion protection system is based on the measured value of the flow rate of the electrolytic solution by the flow meter and the measured value of the hypochlorous acid concentration in the electrolytic solution by the residual salt meter, and at least the hypochlorite flowing in the pipe. It is characterized by having a control unit that controls the addition of a chloric acid remover.

According to the present invention, it is possible to provide an electrocorrosion protection system capable of suitably removing hypochlorous acid even when an anticorrosion voltage of a predetermined value or more is applied, and a seawater desalination plant equipped with the same.
Issues, configurations and effects other than those described above will be clarified by the description of the following embodiments.

It is an overall schematic block diagram of the seawater desalination plant which concerns on one Embodiment of this invention. It is a schematic diagram of the anticorrosion system of Example 1 which concerns on one Example of this invention. It is a vertical cross-sectional view of the anode electrode installation part shown in FIG. It is a functional block diagram of the control unit shown in FIG. It is a schematic diagram of the anticorrosion system of Example 2 which concerns on another Example of this invention. It is a schematic diagram of the anticorrosion system of Example 3 which concerns on another Example of this invention.

In the present specification, the "electrolyte solution" includes seawater (Sea Water: SW), brackish water (BW), brackish water, saline solution, salt water and the like. Here, brackish water refers to water containing salt such as sodium chloride, and brackish water existing at the boundary with seawater is also included in brackish water, and fossil water created by confining seawater in the past and salt in rock salt areas. There is also brackish water in land water such as water containing. In addition, when classified by sodium chloride concentration, less than 0.05% is fresh water, 0.05% or more and less than 0.35% is brackish water, 0.35% or more and less than 0.5% is salt water, and 0.5% or more is salt water. Is called. The concentration of sodium chloride in seawater is about 0.24% to 2.96%, and the concentration varies depending on the sea area. In addition, an aqueous solution containing an arbitrary ionic species is also included in the "electrolyte solution" in the present specification.

When using a metal material as a piping material for equipment used in an environment where corrosion is likely to occur, such as seawater, for example, seawater desalination plant equipment, a sacrificial anode is used as a measure to suppress the occurrence of corrosion on the metal material. It mainly uses one of the methods, the electrocorrosion protection method of the external power supply method, the surface coating method, and the highly corrosion resistant material method. Among these, the external power supply type electrocorrosion protection method is characterized in that the amount of metal elution that causes deterioration of the RO membrane used for seawater desalination is small.
The electrocorrosion protection method is a corrosion protection method that controls electron transfer in a corrosive action. In the external power supply type electrocorrosion protection method, an electrode for generating an electric current is connected to a metal material used as a structural member of a device to be protected against corrosion via a power supply. At this time, the electrodes are brought into contact with an electrolytic solution common to the metal material so that a circuit is formed through the electrolytic solution.
A voltage is applied to the electrode by a power source to and from the metal material to be protected against corrosion. At this time, the case where the electrode is set to a noble potential and used as an anode (anode) and the metal material is set to a low potential and used as a cathode (cathode) is called a cathode protection method. On the contrary, the case where the electrode is set to a low potential and used as a cathode and the metal material is set to a noble potential and used as an anode is called an anode corrosion protection method. Although the present invention can be applied to both the cathode anticorrosion method and the anode anticorrosion method, seawater will be described below as an example by using the cathode anticorrosion method which is often applied to seawater desalination plants.

When the electrode is polarized to a noble potential by a power source, an electrochemical reaction occurs at the interface with the electrolytic solution, and electrons are transferred to the metal material side to be protected against corrosion. At that time, the metal material to be protected from corrosion is polarized to a low potential in which the anodic reaction (corrosion) is reduced by receiving an electron supply.
Examples of the metal material to be protected against corrosion include steel materials such as carbon steel, die steel, nickel cast iron, and low alloy steel. Examples thereof include stainless steels such as austenitic stainless steels, ferrite stainless steels, two-phase stainless steels, martensitic stainless steels, and precipitation hardening stainless steels. Further, copper alloys such as bronze and brass, and nickel-based alloys such as cupronickel and monel can be mentioned. Examples of the manufacturing method include casting, rolling, forging, plating, and welding overlay, so-called 3D printer technology. Welded parts are also subject to corrosion protection. On the other hand, as the material of the electrode, for example, noble metal oxides such as ruthenium oxide, iridium oxide and rhodium oxide, MMO (Mixed Metal Oxide) obtained by combining them, oxides such as iron oxide and titanium oxide, platinum and iridium and the like. Precious metals, alloys such as platinum-titanium, high silicon iron, tantalum, carbon and the like can be mentioned.

An example of such an external power supply type anticorrosion system and a seawater desalination plant equipped with the system will be described below with reference to the drawings. FIG. 1 is an overall schematic configuration diagram of a seawater desalination plant according to an embodiment of the present invention. In FIG. 1, a solid line arrow indicates a flow of water, a dotted line arrow indicates a signal line, and a broken line arrow indicates a flow of a coagulant, a cleaning chemical, or the like.
As shown in FIG. 1, in the seawater desalination plant 1, the raw water storage tank 3 and the MMF (Multi) for storing the taken raw water (electrolyte) in order from the intake of the seawater (raw water) to be treated to the downstream side. Media Filter) 4, ultrafiltration membrane (UF membrane: Ultrafiltration Membrane) 5, intermediate tank 10, pressurizing pump 11, RO membrane module 12 consisting of a pressure vessel accommodating RO membrane element inside, energy recovery device (Energy Recovery) It is composed of a device (ERD) 15, a freshwater storage tank 16, and a concentrated water storage tank 17.
In the raw water storage tank 3, seawater or brine (electrolyte solution) as raw water to be taken is stored. The flocculant is appropriately injected into the raw water storage tank 3 from the flocculant tank 6 for storing the polymer flocculant or the inorganic flocculant via the flocculant injection pump 7. Then, impurities such as organic substances contained in the raw water in the raw water storage tank 3 are captured by the injected flocculant to form flocs. For raw water containing flocs, impurities contained in flocs and raw water are membrane-separated by MMF4 and ultrafiltration membrane 5 by a pump according to the pore size, and the raw water after membrane separation (electrolyte solution: water to be treated). ) Is temporarily stored in the intermediate tank 10. The pretreatment section consists of the process from injection of the flocculant to membrane separation by the ultrafiltration membrane 5. As the polymer flocculant, for example, a polyacrylamide-based flocculant is used, and as the inorganic flocculant, for example, ferric chloride is used.

The raw water (electrolyte solution: water to be treated) stored in the intermediate tank 10 is supplied to the RO membrane module 12 as supply water (electrolyte solution) 18 by the pressurizing pump 11. The supply water (electrolyte solution) 18 is membrane-separated by the RO membrane module 12 into concentrated water 14 which is high-concentration salt water and filtered water (fresh water) 13. The filtered water 13 is supplied to the fresh water storage tank 16 from one end of the RO membrane module 12, and the concentrated water 14 is supplied to the concentrated water storage tank 17 via the energy recovery device 15. The energy recovered by the energy recovery device 15 is used as a part of the power for driving the pressurizing pump 11. The RO membrane element housed in the RO membrane module 12 is cleaned at a desired time by the cleaning chemicals supplied from the cleaning chemical storage tank 8 via the cleaning chemical injection pump 9.

Here, the energy recovery device 15 introduces, for example, a part of the supply water 18 and the high-pressure concentrated water discharged from the RO membrane module 12 into two cylinders, respectively, and the high-pressure concentrated water is introduced through the piston inside the cylinders. DWEER (Dual Work Exchange Energy Recovery) that transfers the pressure of PX (Pressure Exchanger) that transmits the pressure of concentrated water to the seawater side or high-pressure concentrated water is increased in flow velocity by a nozzle with a squeezed tip and directly hits the bucket of the Pelton water wheel to rotate the Pelton water wheel and water. A device that transmits the power to the supply water 18 directly connected to the axle is used.

The monitoring control device 19 monitors the state of the RO membrane module 12 and controls the coagulant injection pump 7, the cleaning chemical injection pump 9, and the pressurizing pump 11.
The configuration of the pretreatment unit is not limited to the above configuration, and for example, a sand filtration unit may be used instead of the MMF4, or the configuration may include only one of the MMF4 and the ultrafiltration membrane 5. It is also good, and an MF membrane (Microfiltration Membrane) may be used.

The inner surface of various pumps such as an intake pump including the pressurizing pump 11 is in contact with seawater (electrolyte solution). Therefore, it is in an environment where corrosion is likely to occur. Further, a metal pipe is used for the pipe portion exposed to the high pressure downstream from the pressure pump 11, and seawater (electrolyte solution) or concentrated water flows at an internal pressure of, for example, 5 MPa or more. In these metal pipes, a corrosion phenomenon depending on the salt concentration occurs over time, and the corrosion rate is particularly high in the flange part which is the pipe joint part and the welded part where the surface structure and the surface roughness are non-uniform. Local corrosion may develop. In order to prevent the occurrence of these corrosions, an electrocorrosion protection system 2 is provided as shown in FIG. In the following, a case where the electric corrosion protection system 2 is installed in a pipe through which the supply water (electrolyte solution) 18 supplied to the RO membrane module 12 by the pressurizing pump 11 passes will be described as an example, but the present invention is limited to this. Instead, the electric corrosion protection system 2 may be installed in a pipe through which the concentrated water 14 passes, and the electric corrosion protection system 2 may be passed through the pipe through which the supply water (electrolyte) 18 passes and the concentrated water 14. It may be configured to be installed on both sides of the flowing pipe. Further, the anticorrosion system 2 may be installed in various pumps whose inner surface is in contact with seawater (electrolyte solution).
Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic view of an anticorrosion system of Example 1 according to an embodiment of the present invention. The electrocorrosion protection system 2 is attached to the sensor installation position A on the RO membrane module 12 side of the anode electrode 21, the corrosion protection power supply 22, and the pipe 32 installed in the pipe 32 connecting the pressurizing pump 11 and the RO membrane module 12. A flow meter 23, a residual salt meter 24, a pH meter 25, and an electrometer 26 are provided. The pipe 32 is connected to the negative terminal of the anticorrosion power supply 22 by a cable, and the anode electrode 21 is connected to the positive terminal of the anticorrosion power supply 22 by a cable. Further, the anticorrosion system 2 includes a hypochlorous acid remover storage tank 27 for accommodating the hypochlorite remover, a hypochlorite remover injection pump 29, and an intermediate tank 10 to the pressurizing pump 11 in the pipe 32. A check valve 31a for preventing the supplied water (electrolyte solution) 18 flowing back to flow back to the hypochlorite removing agent injection pump 29 side, a pH adjusting agent storage tank 28 for accommodating the pH adjusting agent, and pH. A check valve for preventing the supply water (electrolyte solution) 18 flowing through the pipe 32 from the adjusting agent injection pump 30 and the intermediate tank 10 to the pressurizing pump 11 to flow back to the pH adjusting agent injection pump 30 side. It includes 31b and a control unit 20. The hypochlorous acid is removed from the hypochlorous acid remover storage tank 27 to the supply water (electrolyte solution) 18 flowing through the pipe 32 via the hypochlorous acid remover injection pump 29 and the check valve 31a. The position where the agent is injected is on the upstream side of the pressurizing pump 11. Similarly, the position where the pH adjuster is injected from the pH adjuster storage tank 28 into the supply water (electrolyte solution) 18 flowing through the pipe 32 via the pH adjuster injection pump 30 and the check valve 31b is added. It is on the upstream side of the pressure pump 11.

The control unit 20, which will be described in detail later, outputs an applied voltage capable of energizing a desired anticorrosion current to the anticorrosion power source 22 as a command value based on the measured values by the flow meter 23, the residual salt meter 24, the pH meter 25, and the electrometer 26. At the same time, the amount of the hypochlorous acid remover added to the hypochlorite remover injection pump 29 is output as a command value, and the amount of the pH adjuster added to the pH adjuster injection pump 30 is output as a command value.

As described above, the anode electrode 21 is polarized to a noble potential by the anticorrosion power supply 22, and an electrochemical reaction occurs at the interface with the supply water 18 (electrolyte solution) flowing through the pipe 32 to the RO membrane module 12. Is raised, and electrons are transferred to the pipe 32, which is the object of corrosion protection. Further, the pipe 32, which is the object of corrosion protection, is polarized to a low potential in which the anode reaction (corrosion) is reduced by receiving the electron supply. Normally, the anticorrosion voltage applied from the anticorrosion power source 22 to the anode electrode 21 and the pipe 32 is kept constant at a predetermined value. However, if the water quality or the like of the supply water 18 (electrolyte solution), which is the water to be treated flowing through the pipe 32, changes suddenly, the anticorrosion current may drop to a predetermined value or less sufficient to cancel the corrosion current. .. In this case, it is necessary to increase the anticorrosion voltage. Further, when the metal material is actively dissolved or microbially corroded in the pipe 32, the potential of the pipe 32 rises from the initial potential immediately after the start of electrocorrosion protection. At this time, since the potential of the pipe 32 exceeds the range of the potential that is inactive against corrosion and reaches the active region, it is necessary to increase the anticorrosion voltage and lower the potential of the pipe 32 to the initial potential.

As described above, when the anticorrosion voltage is increased, that is, when an anticorrosion voltage of a predetermined value or more is applied to the anode electrode 21 and the pipe 32 from the anticorrosion power supply 22, the subject that flows through the pipe 32 to the RO membrane module 12. Since the supply water 18 (electrolyte solution), which is the treated water, is seawater having a sodium chloride concentration of about 0.24% to 2.96%, the reactions represented by the following formulas (1) and (2) are shown. Generates hypochlorous acid (HClO).
2Cl ⁻ → Cl ₂ + 2e ⁻・ ・ ・ Equation (1)
Cl ₂ + H ₂ O → HClO + HCl ・ ・ ・ Equation (2)
As described above, hypochlorous acid (HClO) has a property of accelerating the deterioration of the RO membrane in the RO membrane module 12.
Therefore, for example, a hypochlorous acid remover such as NaHSO ₃ (sodium bisulfite: SBS) is injected into the supply water 18 (electrolyte solution) flowing through the pipe 32, and the generated hypochlorous acid (HClO). To remove hypochlorous acid (HClO).

Further, during electrocorrosion protection, hydrogen (H ₂ ) is generated by the reaction represented by the following formula (3).
2H ₂ O + 2e ⁻ → H ₂ + 2OH ⁻・ ・ ・ Equation (3)
Therefore, for example, hydrogen generated by injecting a pH adjuster such as NaOH (sodium hydroxide) or KOH (potassium hydroxide) into the supply water 18 (electrolytic solution) flowing through the pipe 32 to neutralize it. Reduce (H ₂ ).

FIG. 3 is a vertical cross-sectional view of the anode electrode installation portion shown in FIG. As shown in FIG. 3, the anode electrode 21 has an annular shape, and is sandwiched between two insulating materials 35a and an insulating material 35b that also form an annular shape, and the flange 34a of one pipe 32 faces the other pipe 32. It is watertightly fastened to the flange 34b by bolts 36 and nuts 37. It is desirable that the inner diameter of the annular anode electrode 21, the inner diameter of the annular insulating material 35a and the insulating material 35b, and the inner diameter of the pipe 32 are the same. Further, by positioning the inner peripheral surface of the annular anode electrode 21, the inner peripheral surface of the annular insulating material 35a and the insulating material 35b, and the inner peripheral surface of the pipe 32 to be continuous, the inside of the pipe 32 is outlined. No flow path resistance is generated with respect to the supply water 18 (electrolyte solution) which is the water to be treated that flows in the direction indicated by the arrow.

Further, since the other pipe 32 facing the one pipe 32 is in a conductive state by the bolt 36, the flange 34a, and the flange 34b, the other pipe 32 facing the one pipe 32 has the same potential. The inner diameter of the through hole of the annular anode electrode 21 through which the bolt 36 is inserted is larger than the outer diameter of the bolt 36, and the anode electrode 21 and the bolt 36 are in a non-contact state. As the insulating material 35a and the insulating material 35b, for example, rubber which is an insulating elastic body or the like is used.

FIG. 4 is a functional block diagram of the control unit 20 shown in FIG. As shown in FIG. 2, the control unit 20 constituting the anticorrosion system 2 includes an input I / F 41, a measured value acquisition unit 42, a storage unit 43, a hypochlorous acid remover addition amount determination unit 44, and a pH adjuster addition. A quantity determination unit 45, an anticorrosion voltage control unit 46, and an output I / F 47 are provided, and these are connected to each other via an internal bus 48. The measurement value acquisition unit 42, the hypochlorite remover addition amount determination unit 44, the pH adjuster addition amount determination unit 45, and the anticorrosion voltage control unit 46 are, for example, storage devices such as a ROM, RAM, and an external storage device (not shown). It is composed of a processor such as a CPU that reads and executes various programs stored in the ROM and stores the arithmetic processing result, which is the execution result, in the RAM or an external storage device.

The input I / F 41 is the measured value of the flow rate of the supply water 18 (electrolyte solution) which is the water to be treated that flows through the pipe 32 to the RO membrane module 12 by the flow meter 23, and the inside of the pipe 32 by the residual salt meter 24. The measured value of the hypochlorous acid concentration (mg / L) in the supply water 18 (electrolytic solution), which is the water to be treated, which flows to the RO membrane module 12, is measured by the measurement value acquisition unit 42 via the internal bath 48. Transfer to. Further, the input I / F 41 is a measured value of the pH of the supply water 18 (electrolyte solution) which is the water to be treated that flows through the pipe 32 from the pH meter 25 to the RO membrane module 12, and the pipe 32 from the electrometer 26. The measured value of the potential of is transferred to the measured value acquisition unit 42 via the internal bus 48.

The measurement value acquisition unit 42 measures the flow rate of the transferred water supply water 18 (electrolyte solution), and the hypochlorite concentration (mg / mg /) in the supply water 18 (electrolyte solution) which is the water to be treated. The measured value of L), the measured value of the pH of the supply water 18 (electrolyte solution) which is the water to be treated, and the measured value of the potential of the pipe 32 are subjected to noise removal or smoothing treatment, etc., via the internal bath 48. The measured value of the flow rate of the supply water 18 (electrolyte solution), which is the water to be treated, which is stored in a predetermined area of the storage unit 43 and has been subjected to noise removal or smoothing treatment, and in the supply water 18 (electrolyte solution). The measured value of the hypochlorous acid concentration (mg / L) was added to the hypochlorite removing agent addition amount determining unit 44, and the measured value of the pH after noise removal or smoothing treatment was added to the pH adjusting agent. The measured value of the potential of the pipe 32 that has been subjected to noise removal or smoothing treatment is transferred to the amount determination unit 45 to the anticorrosion voltage control unit 46 via the internal bus 48, respectively.

The hypochlorous acid remover addition amount determination unit 44 determines the measured value of the flow rate of the supply water 18 (electrolyte solution), which is the water to be treated, transferred from the measurement value acquisition unit 42 or stored in the storage unit 43. The content of hypochlorous acid in the supply water 18 (electrolyte solution), which is the water to be treated, is determined by multiplying the measured value of the chlorite concentration (mg / L). Then, the hypochlorous acid remover addition amount determination unit 44 is next to the obtained hypochlorous acid content equal to or within the range of the hypochlorous acid content ± several% (within a predetermined margin). The amount of the hypochlorous acid remover added is determined and output as a command value to the hypochlorous acid remover injection pump 29 via the internal bath 48 and the output I / F47. As a result, the hypochlorous acid remover injection pump 29 pumps the determined amount of the hypochlorous acid remover from the hypochlorous acid remover storage tank 27, and pressurizes the pump 11 via the check valve 31a. By injecting into the supply water 18 (electrolytic solution), which is the water to be treated that flows through the pipe 32 on the upstream side, the generated hypochlorous acid can be removed, and the RO in the RO membrane module 12 can be removed. Deterioration of the film can be prevented.

The pH adjuster addition amount determining unit 45 neutralizes based on the measured value of the pH of the supply water 18 (electrolytic solution) which is the water to be treated, which is transferred from the measured value acquisition unit 42 or stored in the storage unit 43. Determine the amount of pH adjuster added. In other words, for example, the pH adjuster addition amount determining unit 45 determines the amount of the pH adjuster added so that the measured value of the pH of the supply water 18 (electrolyte solution), which is the water to be treated, is neutral (pH = 7). decide. Then, the pH adjuster addition amount determining unit 45 outputs the determined pH adjuster addition amount to the pH adjuster injection pump 30 as a command value via the internal bus 48 and the output I / F 47.

The anticorrosion voltage control unit 46 applies a voltage applied between the anode electrode 21 and the pipe 32 as an anticorrosion voltage based on the measured value of the potential of the pipe 32 transferred from the measured value acquisition unit 42 or stored in the storage unit 43. It is output as a command value to the anticorrosion power supply 22 via the internal bus 48 and the output I / F47. As described above, for example, when the potential of the pipe 32 rises above the initial potential immediately after the start of electrocorrosion protection, the potential of the pipe 32 exceeds the range of the potential that is inactive against corrosion and reaches the active region. Therefore, the applied voltage that can increase the anticorrosion voltage and lower the potential of the pipe 32 to the initial potential is output to the anticorrosion power supply 22 as a command value.

In this embodiment, the electrocorrosion system 2 includes a pH adjuster storage tank 28, a pH adjuster injection pump 30, and a check valve 31b, and a control unit 20 constituting the electrocorrosion system 2 adds a pH adjuster. Although the configuration having the quantity determining unit 45 has been described, the present invention is not necessarily limited to this, and it is not necessary to have these configurations.

As described above, according to the present embodiment, it is possible to provide an electrocorrosion protection system capable of suitably removing hypochlorous acid even when an anticorrosion voltage equal to or higher than a predetermined value is applied, and a seawater desalination plant equipped with the same. It will be possible.
Further, since hypochlorous acid generated by an increase in the anticorrosion voltage can be removed, deterioration of the RO membrane can be prevented, the life of the RO membrane module can be extended, and the operating cost of the seawater desalination plant can be reduced.
In addition, the potential of the wetted portion of the pipe or pump made of the metal material to be protected against corrosion can be maintained constant, and the surface state of the wetted portion is tentatively changed (for example, active dissolution of the metal material). Even in such a case, it is possible to perform good corrosion protection.

FIG. 5 is a schematic view of the anticorrosion system of Example 2 according to another embodiment of the present invention. In this embodiment, the pipe is a pipe through which the supply water 18 (electrolytic solution), which is the water to be treated, flows from the intermediate tank 10 to the pressurizing pump 11, and the injection position of the hypochlorous acid remover and the pH adjuster. It differs from Example 1 in that the line mixer is provided on the downstream side of the injection position. The same components as those in the first embodiment are designated by the same reference numerals.

As shown in FIG. 5, in the anticorrosion system 2 of this embodiment, the line mixer 33 is connected to the pipe 32 through which the supply water 18 (electrolyte solution) to be treated flows from the intermediate tank 10 to the pressurizing pump 11. Be prepared. The line mixer 33 uses hypochlorite in the supply water (electrolyte solution) 18 that flows from the hypochlorite remover storage tank 27 into the pipe 32 via the hypochlorite remover injection pump 29 and the check valve 31a. The position where the acid remover is injected, and the pH adjuster 18 from the pH adjuster storage tank 28 to the supply water (electrolyte) 18 that flows through the pipe 32 via the pH adjuster injection pump 30 and the check valve 31b. Is arranged on the downstream side of the injection position and on the upstream side of the pressurizing pump 11.

As the line mixer 33, for example, a rotating member is provided, and the rotating member is rotationally driven by an external motor to apply a shearing force to the supply water (electrolyte solution) 18 into which the hypochlorous acid removing agent and the pH adjusting agent are injected. By giving, the hypochlorous acid remover and the pH adjuster are mixed. Further, a so-called static mixer may be used as the line mixer 33. The static mixer is provided with a first spiral fixed wing and a second spiral fixed wing facing each other from the inflow portion to the outflow portion, and is a supply water (electrolyte solution) in which a hypochlorous acid remover and a pH adjuster are injected. The flow of 18 becomes a swirling flow in opposite directions by the first spiral fixed wing and the second spiral fixed wing that face each other, and the hypochlorous acid remover and the pH adjuster interfere with each other. A shearing force is applied to the supplied water (electrolyte solution) 18 in which the hypochlorous acid is injected, and the hypochlorous acid remover and the pH adjuster are mixed.
Since the control unit 20 constituting the anticorrosion system 2 is the same as that of the first embodiment, the description thereof will be omitted.
In this embodiment, the electrocorrosion system 2 includes a pH adjuster storage tank 28, a pH adjuster injection pump 30, and a check valve 31b, and the control unit 20 constituting the electrocorrosion system 2 determines the amount of the pH adjuster added. Although the configuration having the unit 45 has been described, the present invention is not limited to this, and it is not necessary to have these configurations.

As described above, according to this example, the hypochlorous acid remover injected into the electrolytic solution which is the water to be treated can be mixed by the line mixer, and the hypochlorous acid remover can be mixed more effectively in the water to be treated as compared with Example 1. It becomes possible to remove hypochlorous acid.

FIG. 6 is a schematic view of the anticorrosion system of Example 3 according to another embodiment of the present invention. In this embodiment, the pipe 32 through which the supply water (electrolyte solution) 18 to be treated flows from the pressurizing pump 11 to the RO membrane module 12, and is attached to the sensor installation position A on the RO membrane module 12 side. With the first sensor group including the flow meter 23, the residual salt meter 24, the pH meter 25, and the electrometer 26. Example 1 is provided with a second sensor group including a flow meter 23, a residual salt meter 24, a pH meter 25, and an electrometer 26, which are attached to the sensor installation position B on the downstream side of the anode electrode 21. Different from. Further, the position where the hypochlorous acid remover is injected and the position where the pH adjuster is injected are different from those in Example 1, and are downstream from the injection position of the hypochlorous acid remover and the injection position of the pH adjuster. The difference from the first embodiment is that the line mixer 33 is provided on the RO membrane module 12 side. The same reference numerals are given to the same components as in the first embodiment.

As shown in FIG. 6, the anticorrosion system 2 of this embodiment is a pipe 32 connecting the pressurizing pump 11 and the RO membrane module 12, and is a sensor installation position in the vicinity of the anode electrode 21 and on the downstream side thereof. The control unit 20 takes in the measured values from the second sensor group including the flow meter 23, the residual salt meter 24, the pH meter 25, and the electrometer 26 attached to B. Specifically, the flow meter 23 constituting the second sensor group measures the flow rate of the supply water 18 (electrolyte solution) which is the water to be treated immediately after the anode electrode 21 flows, and the residual salt meter 24 treats the water. The measurement value acquisition unit 42 takes in the measured value of the hypochlorous acid concentration (mg / L) in the supply water 18 (electrolyte solution) which is water via the input I / F 41, and performs noise removal or smoothing treatment. It is applied, stored in a predetermined area of the storage unit 43 via the internal bath 48, and transferred to the hypochlorous acid removing agent addition amount determining unit 44. The hypochlorous acid remover addition amount determination unit 44 determines the measured value of the flow rate of the supply water 18 (electrolyte solution), which is the water to be treated, transferred from the measurement value acquisition unit 42 or stored in the storage unit 43. The content of hypochlorous acid in the supply water 18 (electrolyte solution), which is the water to be treated, is determined by multiplying the measured value of the chlorite concentration (mg / L). Then, the hypochlorous acid remover addition amount determination unit 44 adds the hypochlorous acid remover within the range of the obtained hypochlorous acid content equal to or the hypochlorous acid content ± several%. The amount is determined and output as a command value to the hypochlorous acid remover injection pump 29 via the internal bus 48 and the output I / F 47.

Further, the measured value acquisition unit 42 inputs the measured value of the pH of the supply water 18 (electrolyte solution) which is the water to be treated immediately after the anode electrode 21 is passed from the pH meter 25 constituting the second sensor group. It is taken in via F41, subjected to noise removal or smoothing treatment, stored in a predetermined region of the storage unit 43 via the internal bath 48, and transferred to the pH adjuster addition amount determining unit 45. The pH adjuster addition amount determining unit 45 neutralizes based on the measured value of the pH of the supply water 18 (electrolytic solution) which is the water to be treated, which is transferred from the measured value acquisition unit 42 or stored in the storage unit 43. Determine the amount of pH adjuster added. In other words, for example, the pH adjuster addition amount determining unit 45 determines the amount of the pH adjuster added so that the measured value of the pH of the supply water 18 (electrolyte solution), which is the water to be treated, is neutral (pH = 7). decide. Then, the pH adjuster addition amount determining unit 45 outputs the determined pH adjuster addition amount to the pH adjuster injection pump 30 as a command value via the internal bus 48 and the output I / F 47.

The measured value of the potential of the pipe 32 is taken in from the electrometer 26 constituting the second sensor group via the input I / F 41, noise is removed or smoothed, and the internal bus 48 is introduced. It is stored in a predetermined area of the storage unit 43 and transferred to the anticorrosion voltage control unit 46. The anticorrosion voltage control unit 46 applies a voltage applied between the anode electrode 21 and the pipe 32 as an anticorrosion voltage based on the measured value of the potential of the pipe 32 transferred from the measured value acquisition unit 42 or stored in the storage unit 43. It is output as a command value to the anticorrosion power supply 22 via the internal bus 48 and the output I / F47.

The supply water 18 (electrolytic solution), which is the water to be treated into which the hypochlorous acid remover and the pH adjuster are injected, flows into the line mixer 33, and as shown in Example 2 above, the line mixer 33 is operated. A shearing force is applied to the supply water (electrolyte solution) 18 which is the water to be treated into which the hypochlorous acid remover and the pH adjuster are injected during the flow, and the hypochlorous acid remover and the pH adjuster are released. Be mixed. The supply water (electrolyte solution) 18, which is the water to be treated in which the hypochlorous acid remover and the pH adjuster are mixed, is a flow meter 23, a residual salt meter 24, which are attached to the sensor installation position A on the RO membrane module 12 side. The control unit 20 takes in the measured values from the first sensor group including the pH meter 25 and the electrometer 26. Specifically, the flow rate of the supply water (electrolyte solution) 18 which is the water to be treated in which the hypochlorous acid remover and the pH adjuster are mixed by the line mixer 33 by the flow meter 23 constituting the first sensor group. The measured value of the hypochlorous acid concentration (mg / L) in the supply water 18 (electrolytic solution), which is the water to be treated, is input by the measured value acquisition unit 42 via the input I / F 41. It is taken in, noise-removed or smoothed, stored in a predetermined area of the storage unit 43 via the internal bus 48, and transferred to the hypochlorous acid remover addition amount determining unit 44. The hypochlorous acid remover addition amount determination unit 44 determines the measured value of the flow rate of the supply water 18 (electrolyte solution), which is the water to be treated, transferred from the measurement value acquisition unit 42 or stored in the storage unit 43. The content of hypochlorous acid in the supply water 18 (electrolyte solution), which is the water to be treated, is determined by multiplying the measured value of the chlorite concentration (mg / L). Then, the hypochlorous acid remover addition amount determination unit 44 adds the hypochlorous acid remover within the range of the obtained hypochlorous acid content equal to or the hypochlorous acid content ± several%. The amount is determined and output as a command value to the hypochlorous acid remover injection pump 29 via the internal bus 48 and the output I / F 47. That is, feedback control is performed with respect to the injection of the hypochlorous acid remover.

Further, the measured value of the pH of the supply water (electrolyte solution) 18 which is the water to be treated in which the hypochlorous acid remover and the pH adjuster are mixed by the line mixer 33 from the pH meter 25 constituting the first sensor group. Is taken in by the measured value acquisition unit 42 via the input I / F 41, subjected to noise removal or smoothing processing, etc., stored in a predetermined region of the storage unit 43 via the internal bus 48, and the amount of the pH adjuster added is determined. Transfer to unit 45. The pH adjuster addition amount determining unit 45 neutralizes based on the measured value of the pH of the supply water 18 (electrolytic solution) which is the water to be treated, which is transferred from the measured value acquisition unit 42 or stored in the storage unit 43. Determine the amount of pH adjuster added. In other words, for example, the pH adjuster addition amount determining unit 45 determines the amount of the pH adjuster added so that the measured value of the pH of the supply water 18 (electrolyte solution), which is the water to be treated, is neutral (pH = 7). decide. Then, the pH adjuster addition amount determining unit 45 outputs the determined pH adjuster addition amount to the pH adjuster injection pump 30 as a command value via the internal bus 48 and the output I / F 47. That is, feedback control is performed with respect to the injection of the pH regulator.

The measured value of the potential of the pipe 32 is taken in from the electrometer 26 constituting the first sensor group via the input I / F 41, noise is removed or smoothed, and the internal bus 48 is introduced. It is stored in a predetermined area of the storage unit 43 and transferred to the anticorrosion voltage control unit 46. The anticorrosion voltage control unit 46 applies a voltage applied between the anode electrode 21 and the pipe 32 as an anticorrosion voltage based on the measured value of the potential of the pipe 32 transferred from the measured value acquisition unit 42 or stored in the storage unit 43. It is output as a command value to the anticorrosion power supply 22 via the internal bus 48 and the output I / F47.
In the anticorrosion system 2 of the present embodiment, the water flow meter 23, the residual salt meter 24, the pH meter 25, and the electrometer 26 constituting the second sensor group supply water to be treated immediately after the anode electrode 21 flows. The water (electrolyte solution) 18 is monitored, and the injection control of the hypochlorite remover and the pH adjuster and the control of the anticorrosion voltage are executed. On top of that, the water to be treated mixed with the hypochlorous acid remover and the pH adjuster by the flow meter 23, the residual salt meter 24, the pH meter 25, and the electrometer 26 constituting the second sensor group. A certain supply water (electrolyte solution) 18 is monitored and feedback control is executed.

In this embodiment, the electrocorrosion system 2 includes a pH adjuster storage tank 28, a pH adjuster injection pump 30, and a check valve 31b, and a control unit 20 constituting the electrocorrosion system 2 adds a pH adjuster. Although the configuration having the quantity determining unit 45 has been described, the present invention is not necessarily limited to this, and it is not necessary to have these configurations. Further, the line mixer 33 does not necessarily have to be provided.

As described above, according to the present embodiment, in addition to the effect of the first embodiment, the water to be treated (electrolyte solution) flowing into the RO membrane module and the water to be treated (electrolyte solution) immediately after the anode electrode flows from the viewpoint of overall control. ) Is monitored and feedback control is performed, so that the amount of the hypochlorous acid removing agent added and the anticorrosion voltage can be controlled with higher accuracy.

The present invention is not limited to the above-mentioned examples, and includes various modifications. For example, the above-described embodiment has been described in detail in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to those having all the described configurations.

1 ... Seawater desalination plant 2 ... Electrocorrosion protection system 3 ... Raw water storage tank 4 ... MMF
5 ... Ultrafiltration membrane 6 ... Coagulant tank 7 ... Coagulant injection pump 8 ... Cleaning chemical storage tank 9 ... Cleaning chemical injection pump 10 ... Intermediate tank 11 ... Addition Pressure pump 12 ... RO membrane module 13 ... Filtered water (fresh water)
14 ... Concentrated water 15 ... Energy recovery device 16 ... Fresh water storage tank 17 ... Concentrated water storage tank 18 ... Supply water 19 ... Monitoring control device 20 ... Control unit 21 ...・ Anode electrode 22 ・ ・ ・ Anticorrosion power supply 23 ・ ・ ・ Flow meter 24 ・ ・ ・ Residual salt meter 25 ・ ・ ・ pH meter 26 ・ ・ ・ Potential meter 27 ・ ・ ・ Hypochlorite remover storage tank 28 ・ ・ ・pH adjuster storage tank 29 ... Hypochlorite remover injection pump 30 ... pH adjuster injection pump 31a, 31b ... Check valve 32 ... Piping 33 ... Line mixer 34a, 34b ... .. Flange 35a, 35b ... Insulation material 36 ... Bolt 37 ... Nut 41 ... Input I / F
42 ... Measurement value acquisition unit 43 ... Storage unit 44 ... Hypochlorous acid remover addition amount determination unit 45 ... pH adjuster addition amount determination unit 46 ... Corrosion protection voltage control unit 47 ...・ Output I / F
48 ... Internal bus

Claims (16)

At least, electrodes arranged via an insulating material in a pipe made of a metal material through which an electrolytic solution flows,
An anticorrosion power source that applies a voltage between the electrode and a pipe made of the metal material,
At least, a flow meter installed in the pipe made of the metal material and measuring the flow rate of the electrolytic solution flowing through the pipe, and a residual salt meter measuring the concentration of hypochlorous acid in the electrolytic solution flowing through the pipe. With
Hypochlorous acid having at least a reducing action on the electrolytic solution flowing in the pipe based on the measured value of the flow rate of the electrolytic solution by the flow meter and the measured value of the hypochlorous acid concentration in the electrolytic solution by the residual salt meter. An electrocorrosion protection system characterized by having a control unit that controls the addition of a remover. In the anticorrosion system according to claim 1,
It has a pH meter that measures the pH of the electrolytic solution that is installed in the pipe made of the metal material and flows through the pipe.
The control unit is an anticorrosion system characterized in that it controls to add a pH adjuster to an electrolytic solution flowing through a pipe based on a measured value of the pH meter. In the anticorrosion system according to claim 2.
And hypochlorous acid removal agent reservoir for containing the hypochlorite removers,
Hypochlorous acid remover injection pump and
The first check valve and
A pH adjuster storage tank that houses the pH adjuster,
With a pH regulator injection pump,
With a second check valve,
Based on the command from the control unit, the injecting the hypochlorous acid removal agent to the electrolytic solution flowing through the pipe via the first check valve by the hypochlorous acid removing agent infusion pump, the An electrocorrosion protection system characterized in that a pH adjuster is injected into an electrolytic solution flowing through a pipe via the second check valve by a pH adjuster injection pump. In the anticorrosion system according to claim 3.
The control unit
The hypochlorous acid content in the electrolytic solution was obtained from the product of the measured value of the flow rate of the electrolytic solution by the flow meter and the measured value of the hypochlorous acid concentration in the electrolytic solution by the residual salt meter, and the obtained hypochlorous acid was obtained. determining the amount of the hypochlorous acid removing agent in chlorate content in equivalent amounts or predetermined tolerance, adding hypochlorous acid removal agent to be output to the hypochlorous acid removing agent infusion pump as a command value An electrocorrosion protection system characterized by having a quantity determining unit. In the anticorrosion system according to claim 4.
The control unit
It is characterized by having a pH adjuster addition amount determining unit that determines the addition amount of the pH adjuster at which the pH measurement value of the electrolytic solution by the pH meter becomes neutral and outputs it as a command value to the pH adjuster injection pump. Electro-corrosion system. In the anticorrosion system according to claim 5.
Equipped with an electrometer that measures the potential of a pipe made of the metal material through which the electrolytic solution flows.
The control unit
Based on the measured value of the potential of the pipe made of the metal material by the electrometer, the voltage applied between the electrode and the pipe made of the metal material so that the potential of the pipe made of the metal material becomes a predetermined potential. An electric anticorrosion system characterized by having an anticorrosion voltage control unit that outputs the command value to the anticorrosion power source. In the anticorrosion system according to claim 6.
Comprising a line mixer disposed in a downstream side of a position to inject the pH adjusting agent positions and the pipe to inject the hypochlorite removal agent in the electrolyte solution flowing through the pipe in the electrolyte solution flowing through,
Said line mixer, cathodic protection system, wherein the hypochlorous acid removing agent and pH adjusting agent are mixed giving shearing force to the injected electrolyte. In the anticorrosion system according to claim 6.
A downstream side of the electrode, and, from the position of injecting a pH adjusting agent positions and the pipe to inject the hypochlorite removing agent in the electrolyte solution flowing in the pipe in the electrolyte flowing through A first sensor group including the flow meter, the residual salt meter, the pH meter, and the electrometer, which are arranged on the downstream side.
A upstream side of a position to inject the pH adjusting agent positions and the pipe to inject the hypochlorite removal agent in the electrolyte solution flowing through the pipe in the electrolyte solution flowing through, and the electrode A second sensor group including the flow meter, the residual salt meter, the pH meter, and the electrometer, which are arranged on the downstream side in the vicinity, is provided.
Wherein the control unit, based on said measurements from the second sensor group, injected with the hypochlorous acid removal and pH adjusting agents to the electrolytic solution flowing through the at least the pipe, further, the first sensor An electrocorrosion protection system comprising feedback control of the hypochlorous acid removing agent injection pump, the pH adjusting agent injection pump, and the anticorrosion power source based on the measured values from the group. A pressurizing pump that pressurizes the seawater treated by the pretreatment section,
A reverse osmosis membrane module that introduces seawater pressurized by the pressurizing pump and separates it into concentrated water and filtered water, which are high-concentration salt water.
An energy recovery device that introduces concentrated water discharged from the reverse osmosis membrane module and recovers energy as part of the power for driving the pressurizing pump.
A pipe that connects the pressurizing pump and the reverse osmosis membrane module and allows pressurized seawater to flow through,
A pipe that connects the reverse osmosis membrane module and the energy recovery device and allows concentrated water to flow through,
An electrode arranged via an insulating material in a pipe through which the pressurized seawater flows and / or a pipe through which the concentrated water flows, a pipe through which the electrode and the pressurized seawater flow, and / Alternatively, it is installed in an anticorrosion power source that applies a voltage between the pipe through which the concentrated water flows, a pipe through which pressurized seawater flows, and / or a pipe through which the concentrated water flows, and flows through the pipe. An anticorrosion system having a flow meter for measuring the flow rate of pressurized seawater and / or concentrated water and a residual salt meter for measuring the concentration of hypochlorite in the pressurized seawater and / or concentrated water. Prepare,
The electrocorrosion system has a measured value of the flow rate of pressurized seawater and / or concentrated water by the flow meter and a measured value of hypochlorous acid concentration in the pressurized seawater and / or concentrated water by the residual salt meter. A seawater desalination plant characterized in that it has a control unit that controls the addition of a hypochlorous acid remover having at least a reducing action to the pressurized seawater and / or concentrated water flowing through the pipe. .. In the seawater desalination plant according to claim 9.
It has a pH meter that is installed in the pipe through which the pressurized seawater flows and / or in the pipe through which the concentrated water flows and measures the pH of the pressurized seawater and / or the concentrated water that flows through the pipe. And
The control is a seawater desalination plant characterized in that a pH adjuster is added to pressurized seawater and / or concentrated water flowing through a pipe based on a measured value of the pH meter. In the seawater desalination plant according to claim 10.
And hypochlorous acid removal agent reservoir for containing the hypochlorite removers,
Hypochlorous acid remover injection pump and
The first check valve and
A pH adjuster storage tank that houses the pH adjuster,
With a pH regulator injection pump,
With a second check valve,
Based on the command from the control unit, the hypochlorite said to hypochlorous acid removing agent seawater pressurized flowing through the pipe via the first check valve by means of an infusion pump and / or concentrated water Along with injecting the removing agent, the pH adjusting agent is injected into the pressurized seawater and / or concentrated water flowing through the pipe through the second check valve by the pH adjusting agent injection pump. Seawater desalination plant. In the seawater desalination plant according to claim 11.
The control unit
Pressurized by the product of the measured value of the flow rate of pressurized seawater and / or concentrated water by the flow meter and the measured value of the hypochlorous acid concentration in the pressurized seawater and / or concentrated water by the residual salt meter. seawater and / or determine the hypochlorite content of the concentrate water to determine the amount of the hypochlorous acid removing agent in the obtained hypochlorite content an equivalent amount or a predetermined tolerance, A seawater desalination plant characterized by having a hypochlorous acid remover addition amount determining unit that outputs to the hypochlorous acid remover injection pump as a command value. In the seawater desalination plant according to claim 12,
The control unit
The amount of pH adjuster added is determined by the pH measurement value of the pressurized seawater and / or concentrated water by the pH meter, and is output to the pH adjuster injection pump as a command value. A seawater desalination plant characterized by having a determination unit. In the seawater desalination plant according to claim 13.
Equipped with an electrometer to measure the potential of the pipe through which pressurized seawater and / or concentrated water flows.
The control unit
Based on the measured value of the potential of the pipe through which the pressurized seawater and / or concentrated water flows by the potential meter, the potential of the pipe through which the pressurized seawater and / or concentrated water flows is a predetermined potential. It is characterized by having an anticorrosion voltage control unit that outputs a voltage applied between the electrode and the pipe through which the pressurized seawater and / or concentrated water flows as a command value to the anticorrosion power source. Seawater desalination plant. In the seawater desalination plant according to claim 14.
A pH adjusting agent to the position and the seawater in the pipe pressurized flowing and / or concentrated water injecting the hypochlorite removing agent in seawater and / or concentrated water pressurized flowing through the pipe Equipped with a line mixer located downstream from the injection position
It said line mixer, seawater desalination plants, which comprises mixing giving shearing force to the hypochlorous acid removal agent and pH seawater modifier is pressurized is injected and / or concentrated water. In the seawater desalination plant according to claim 14.
A downstream side of the electrode, and pressurized flows through the location and the pipe for injecting the hypochlorous acid removal agent in the pipe to the pressurized seawater and / or concentrated water flowing A first sensor group consisting of the flow meter, the residual salt meter, the pH meter, and the electrometer, which are arranged downstream from the position where the pH adjuster is injected into the seawater and / or the concentrated water.
A pH adjusting agent to the position and the seawater in the pipe pressurized flowing and / or concentrated water injecting the hypochlorite removing agent in seawater and / or concentrated water pressurized flowing through the pipe A second sensor group consisting of the flow meter, the residual salt meter, the pH meter, and the electrometer, which is located on the upstream side of the injection position and on the downstream side in the vicinity of the electrode. With
Wherein the control unit, based on said measurements from the second sensor group, injected with the hypochlorous acid removal and pH adjusting agents to at least the seawater in the pipe pressurized flowing and / or concentrated water Further, a seawater desalination plant characterized in that the hypochlorous acid removing agent injection pump, the pH adjusting agent injection pump and the anticorrosion power source are feedback-controlled based on the measured values from the first sensor group.

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