JP7312593B2 - Liquid handling system and adsorption system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a liquid treatment system and an adsorption system that suppress crevice corrosion of metal materials that form wetted parts.

Stainless steels such as SUS304 and SUS316L are general-purpose materials having both corrosion resistance and economy, and are used as corrosion-resistant materials in various fields such as nuclear reactor facilities and chemical facilities. Stainless steel not only exhibits high corrosion resistance due to the dense passive film formed on the surface by oxidation, but also saves expensive metal elements such as nickel.

Stainless steel is generally a material with excellent corrosion resistance, but in the presence of chloride ions, under high temperature conditions, under acidic conditions, etc., localized corrosion such as pitting corrosion and crevice corrosion may occur. In addition, intergranular corrosion may occur depending on the chemical composition, thermal influence, etc., and stress corrosion cracking may occur due to superimposition of causative factors such as stress. Therefore, when stainless steel is used for devices and equipment, it is necessary to take measures against corrosion so as not to cause serious damage.

In particular, in liquid treatment systems that handle liquids containing chloride ions, it is known that crevice corrosion is likely to occur and progress in wetted parts where the liquid comes into contact, especially in equipment where scale is likely to adhere, welded parts and heat-affected parts such as pipes, flange joints where gaps are likely to form, and near the boundaries of sludge pools. Therefore, there is a need for protection against crevice corrosion for such liquid treatment systems.

2. Description of the Related Art Conventionally, various techniques of injecting a chemical substance into a liquid that contacts a metal material have been proposed in order to suppress corrosion of liquid-contacting parts of devices and equipment.

For example, Patent Document 1 describes a method for suppressing crevice corrosion of stainless steel in which anions other than chloride ions coexist in an aqueous system at a molar concentration equal to or higher than the molar concentration of chloride ions in the aqueous system. In Patent Document 1, sulfate ions are used as anions. Chloride ion concentrations range from 0.01 millimoles/liter to less than 10 millimoles/liter.

In addition, Patent Document 2 describes a corrosion prevention method for stainless steel piping for miscellaneous water supply in which the Cl ⁻ concentration is 100 ppm or more and the M alkalinity Yppm converted to CaCO ₃ is out of the range shown by the following formula: Y<−0.02X+40 where the Cl ⁻ concentration is Xppm.

In addition, Patent Document 3 describes a corrosion prevention method for stainless steel members in which a solution containing hydrogen peroxide is added to the seawater to be handled in a facility that handles various types of seawater, thereby repairing or maintaining a passive film on the surface of the stainless steel members that come into contact with the seawater. In Patent Document 3, the addition of a mixed solution of hydrogen peroxide, peracetic acid, and acetic acid or the like has resulted in the prevention of crevice corrosion.

Further, Patent Document 4 describes a method for suppressing corrosion of carbon steel by adding Na ₂ MoO ₄ and NaNO ₃ to pure water to prepare a corrosion inhibitor solution, degassing the corrosion inhibitor solution, and injecting the corrosion inhibitor solution into an aqueous solution containing chloride ions in contact with carbon steel to obtain a corrosion inhibitor-containing solution. In Patent Document 4, Na ₂ MoO ₄ contained in the corrosion inhibitor-containing liquid is in the range of 50 to 5000 ppm, and NaNO ₃ is in the range of 50 to 500 ppm.

Further, Patent Document 5 describes a method for preventing crevice corrosion of a corrosion-resistant metal material in an aqueous solution containing chloride ions and ozone, in which nitrate ions are allowed to coexist in the aqueous solution at a molar concentration ratio of 0.2 or more with respect to the molar concentration of chloride ions. In Patent Document 5, austenitic stainless steels such as SUS304, SUS316L, and SUS317L are tested as corrosion-resistant metal materials.

Further, Patent Document 6 describes a method for suppressing localized corrosion of stainless steel in a wet environment where radiation is irradiated, wherein nitrate ions with a molar concentration of 1 or more times the molar concentration of chloride ions contained in the water are allowed to coexist in the water coming into contact with the stainless steel. In Patent Document 6, austenitic stainless steels such as SUS304 and SUS316L are immersed in a solution of sodium nitrate and tested.

Further, Patent Document 7 describes a method for suppressing local corrosion of stainless steel in a wet environment where radiation is irradiated, in which the pH of water in contact with stainless steel is adjusted to 12.5 or higher. In Patent Document 7, crevice corrosion is prevented by adding sodium hydroxide, calcium hydroxide, or the like.

Patent Document 8 describes a radioactive waste liquid treatment apparatus that removes chlorine ions from a radioactive waste liquid concentrated by an evaporative concentrator. In Patent Document 8, chlorine, which causes corrosion and is contained in the concentrated radioactive waste liquid, is removed by electrolytic treatment to generate chlorine gas or precipitation treatment to generate silver chloride.

JP 2009-270131 A JP-A-10-219484 JP 2010-280947 A JP 2015-025155 A JP 2015-067859 A JP 2017-218656 A Japanese Patent Application Laid-Open No. 2018-040038 JP 2013-148365 A

As described in Patent Documents 1 to 7, corrosion of metal materials is prevented by injecting a chemical substance such as an anion into a liquid that contacts the metal materials. However, among various liquid treatment systems, there are devices that handle liquids containing high concentrations of chloride ions and liquids containing radioactive substances, and these factors increase the susceptibility to corrosion, so corrosion of metal materials is still a concern.

In the conventional technology, when the liquid to be handled contains a high concentration of chloride ions and is under acidic conditions with a low pH, there is a problem that the occurrence and progression of localized corrosion, especially crevice corrosion, of metal materials that make up the wetted parts cannot be sufficiently suppressed.

As a method for preventing localized corrosion of the metal material forming the wetted portion, as described in Patent Document 8, a method of removing chemical substances such as chloride ions that promote corrosion is conceivable. However, such a method requires new additions such as a deionization device, a filtration device for separating chlorides and the like, a chemical component adjustment device for facilitating removal of chemical substances, etc., and the problem is that the cost of the device increases.

As other methods for preventing localized corrosion of the metal material forming the wetted portion, a method of performing cathodic protection and a method of using a sacrificial anode can be considered. However, in such a method, the structural materials constituting the wetted parts of the liquid treatment system become complicated, the equipment cost increases, and waste is generated, which raises the operating cost.

2. Description of the Related Art In a liquid treatment system handling various liquids, corrosion of metal materials constituting liquid-contacting parts necessitates repair or replacement of the metal materials, and there is also a risk of liquid leakage, etc., which impairs the reliability of the system. Therefore, there is a demand for a system that sufficiently suppresses localized corrosion of the metal material that constitutes the wetted portion by practical and simple means.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a liquid treatment system and an adsorption system that are resistant to localized corrosion of the structural materials of the wetted parts that come into contact with the liquid to be treated, and that have a long service life and high reliability.

As a result of extensive research, the present inventors have found that, unlike sulfate ions, specific inorganic ions such as nitrate ions and molybdate ions exhibit an effect of suppressing localized corrosion of stainless steel under acidic conditions in which chloride ions are present, and that these specific inorganic ions are highly effective when the concentration of these specific inorganic ions is greater than or equal to a specific concentration relative to chloride ions, leading to the completion of the present invention.

前記課題を解決するために本発明に係る液体処理システムは、被処理液の性質、状態又は成分量の調整を行う液体処理システムであって、前記被処理液に接液する接液部の少なくとも一部が金属材料で形成されており、前記金属材料のすきま腐食を抑制するための抑制剤を前記被処理液に注入する抑制剤注入装置と、前記被処理液のｐＨを低下させるためのｐＨ調整剤を注入するｐＨ調整剤注入装置と、を備え、前記被処理液は、塩化物イオンを含む液体であり、前記抑制剤は、モリブデン酸イオンを含有する液体であり、前記金属材料は、二相系ステンレス鋼であり、前記抑制剤が注入された被処理液は、ｐＨが６．０未満であり、且つ、モリブデン酸イオンのモル濃度と塩化物イオンのモル濃度との比が０．１以上、ｐＨが６．０以上８．０以下であり、且つ、モリブデン酸イオンのモル濃度と塩化物イオンのモル濃度との比が０．００７以上に調整される。 The metal material is austenitic stainless steel, and the liquid to be treated into which the inhibitor is injected has a pH of less than 6.0, a ratio of the molar concentration of molybdate ions to the chloride ions of 0.2 or more, a pH of 6.0 to 8.0, and a ratio of the molar concentrations of molybdate ions to the chloride ions of 0.1 or more.

また、本発明に係る吸着システムは、被処理液に含まれる物質を吸着によって除去する吸着システムであって、前記被処理液に接液する接液部の少なくとも一部が金属材料で形成されており、前記被処理液に接液する接液部の少なくとも一部が金属材料で形成されており、被処理液に含まれる物質を吸着する吸着材を有する吸着塔と、前記金属材料のすきま腐食を抑制するための抑制剤を前記被処理液に注入する抑制剤注入装置と、前記被処理液のｐＨを低下させるためのｐＨ調整剤を注入するｐＨ調整剤注入装置と、を備え、前記被処理液は、塩化物イオンを含む液体であり、前記抑制剤は、モリブデン酸イオンを含有する液体であり、前記被処理液は、塩化物イオンを含む液体であり、前記抑制剤は、モリブデン酸イオンを含有する液体であり、前記金属材料は、二相系ステンレス鋼であり、前記抑制剤が注入された被処理液は、ｐＨが６．０未満であり、且つ、モリブデン酸イオンのモル濃度と塩化物イオンのモル濃度との比が０．１以上、ｐＨが６．０以上８．０以下であり、且つ、モリブデン酸イオンのモル濃度と塩化物イオンのモル濃度との比が０．００７以上に調整される。 The metal material is austenitic stainless steel, and the liquid to be treated into which the inhibitor is injected has a pH of less than 6.0, a ratio of the molar concentration of molybdate ions to the chloride ions of 0.2 or more, a pH of 6.0 to 8.0, and a ratio of the molar concentrations of molybdate ions to the chloride ions of 0.1 or more.

According to the present invention, it is possible to provide a long-life and highly reliable liquid treatment system and adsorption system in which the structural material of the wetted portion that is in contact with the liquid to be treated is less susceptible to localized corrosion.

Fig. 2 is a current-time polarization curve obtained in a corrosion test of a welded specimen with a gap made of stainless steel; It is a figure which shows the shape of a welding test piece. It is a longitudinal cross-sectional view showing a welded test piece with a gap. FIG. 3 is a diagram showing a test apparatus used for corrosion tests of welded test pieces with gaps. FIG. 4 is a diagram showing the relationship between the concentration of potassium nitrate and the concentration of chlorine required to suppress crevice corrosion of S32750. FIG. 4 is a diagram showing the relationship between the concentration of sodium molybdate and chlorine concentration required to suppress crevice corrosion of S32750. FIG. 4 is a diagram showing the relationship between the concentration of potassium nitrate and the concentration of chlorine required to suppress crevice corrosion of SUS316L; FIG. 4 is a diagram showing the relationship between the concentration of sodium molybdate and the concentration of chlorine required to suppress crevice corrosion of SUS316L; It is a figure which shows the structure of the adsorption system which is an example of a liquid treatment system. It is a figure which shows the structure of the waste-liquid-treatment system which is an example of a liquid-treatment system. 1 is a diagram showing the configuration of a crevice corrosion monitor device used for monitoring crevice corrosion. FIG. FIG. 4 is a diagram showing changes over time in the corrosion current, the concentration of nitrate ions, the concentration of chloride ions contained in the liquid to be treated, and the pH of the liquid to be treated when potassium nitrate is injected into the liquid to be treated in the adsorption system. FIG. 4 is a diagram showing changes over time in the corrosion current, the concentration of sulfate ions, the concentration of chloride ions contained in the liquid to be treated, and the pH of the liquid to be treated when sodium sulfate is injected into the liquid to be treated in the adsorption system. FIG. 4 is a diagram showing temporal changes in corrosion current, concentration of molybdate ions, concentration of chloride ions contained in the liquid to be treated, and pH of the liquid to be treated when sodium molybdate is injected into the liquid to be treated in the adsorption system.

A liquid treatment system and an adsorption system according to one embodiment of the present invention will be described below. In addition, the same code|symbol is attached|subjected about the structure which is common in each following figure, and the overlapping description is abbreviate|omitted.

The liquid treatment system according to the present embodiment is an apparatus that performs various treatments on liquid and adjusts the property, state, component amount, and the like of the liquid (to-be-treated liquid). In this liquid treatment system, at least a portion of the liquid contacting portion that contacts the liquid to be treated is made of a metal material, and a specific inhibitor, which will be described later, is injected into the liquid to be treated to suppress the occurrence and progress of localized corrosion of the metal material that constitutes the liquid contacting portion of the apparatus/equipment.

Examples of the treatment to be applied to the liquid to be treated include various treatments such as heating, cooling, evaporation, condensation, pressurization, decompression, concentration, dilution, dissolution, coagulation/precipitation, gas-liquid mixing, liquid-liquid mixing, solid-liquid mixing, pH adjustment, viscosity adjustment, component concentration adjustment, addition, separation and removal of components. The liquid treatment system may be a device that performs one of these treatments, or a device that performs a plurality of them.

Specific examples of the liquid treatment system include a waste liquid treatment system that treats radioactive waste liquid generated in a nuclear reactor facility and radioactive waste liquid generated by washing contaminated soil contaminated with radioactive substances, a contaminated water treatment system that treats contaminated water containing radioactive substances, an adsorption system that separates and removes substances in liquid, a seawater desalination system, a seawater concentration system, a seawater pump, and other reactor facility seawater systems.

The liquid-contacting part to suppress crevice corrosion may be a part immersed in the liquid to be treated, a part to be hit by the liquid to be treated, a part to which splashes or droplets of the liquid to be treated adhere, a part to be contacted by the vapor of the liquid to be treated, or the like.

The metal material that constitutes the wetted part that is the object of suppressing crevice corrosion may be a structural material or component material that constitutes a device or device in the system, or may be a pipe or the like connected to the device or device. Apparatus/instruments include various processing apparatuses themselves for physically or chemically treating the liquid to be processed, and pumps, valves, sensors, tanks, pools, etc. attached to or built into the processing apparatuses and piping.

Examples of the metal material forming the wetted portion include stainless steel. Examples of stainless steel include austenitic stainless steel, ferritic stainless steel, duplex stainless steel, and martensitic stainless steel. As the stainless steel, a corrosion-resistant material having a Pitting Resistance Equivalent (PRE) of 18 or more, which is represented by the following formula (1), is preferable.
PRE=%Cr+3.3×%Mo+16×%N (1)

Here, an inhibitor to be injected into the liquid to be treated for suppressing crevice corrosion of metal materials will be described.

FIG. 1 is a current-time polarization curve obtained from a corrosion test of crevice welded specimens made of stainless steel. FIG. 2 is a diagram showing the shape of a weld test piece. FIG. 3 is a vertical cross-sectional view showing a welded test piece with a gap. FIG. 4 is a diagram showing a testing apparatus used for corrosion testing of welded test pieces with gaps.

In FIG. 1, a test piece with a gap formed with a gap is immersed in an aqueous solution (chloride ion concentration: 20000 ppm) adjusted to pH 3.5 with hydrochloric acid, and the electrode potential is polarized at 200 mV. Shows the change in current value over time. The lower curve is the result when the concentration of potassium nitrate is 0.1M, and the upper curve is the result when no potassium nitrate is added (0M).

A test piece with a gap was prepared by preparing a welded metal 100 shown in FIG. 2 using S32750, which is a duplex stainless steel, and forming a gap in the test piece. The left side of FIG. 2 is a front view of the weld test piece 100, and the right side is a side view of the weld test piece 100. FIG. FIG. 3 is a side view of the weld test piece 100 shown in FIG. 2 in which a gap is formed.

The welded test piece 100 was produced by butt-welding two steel plates 100a and 100b having a width (W) of 20.0 mm and a thickness (t) of 2 mm with an I-shaped groove so as to have a length (L) of 50.0 mm. The length (bead width) (X) of the welded portion 120 and the length (l) of the steel plate to be welded were 15 mm at maximum.

The weld metal used was UNS_S32750, which has a high pitting resistance index (PRE) and high resistance to localized corrosion. The chemical composition of S32750 is C: ≤ 0.030, Si: ≤ 0.80, Mn: ≤ 1.20, P: ≤ 0.035, S: ≤ 0.020, Ni: 6.0 to 8.0, Cr: 24.0 to 26.0, Mo: 3.0 to 5.0, Cu ≤ 0.50, N: 0.24 to 0.32. PRE (=%Cr+3.3×%Mo+16×%N)≧41.

The welded test piece 100 was coated with a chemical-resistant insulating tape made of PTFE so that the 30.0 mm long portion on the lower side where the welded portion 120 was provided was in contact with the test solution. The surface of the test piece was left as received, and was only cleaned with acetone without polishing, passivation, or the like.

As shown in FIG. 3 , the gapped test piece 150 was produced by forming a gap in the surface of the welded test piece 100 with the impression material 130 . As the impression material 130, a dental impression material made of vinyl silicone (manufactured by GC Corporation) was used.

First, the impression material 130 was pressed against the surface of the welded portion 120 , a mold of the surface of the weld bead was taken, and the impression material 130 was once peeled off from the weld test piece 100 . Then, the surroundings of the impression material 130 were removed, and only a molded portion having a length of 20.0 mm and a width of 20.0 mm was cut out. Subsequently, the cut-out impression material 130 was again fitted to the surface of the weld bead, and an insulating tape was wrapped around the weld test piece 100 and the impression material 130 . Then, the top and bottom of the impression material 130 were fixed with fluororesin cable ties to form a gap between the surface of the weld test piece 100 and the impression material 130 .

The corrosion test was carried out using a measurement apparatus combining a constant temperature bath 200, an electrolytic bath 210, an electrode bath 220, a test electrode 201, a counter electrode 202, a reference electrode 203, and a potentiostat 250, as shown in FIG.

As the test electrode 201, a welding test piece with a gap (see FIG. 3) connected to a lead wire was used. A platinum electrode was used as the counter electrode 202 . As the reference electrode 203, a silver-silver chloride electrode was used. The electrolytic cell 210 was fitted with a vent tube 230 for deaeration by bubbling an inert gas through the test solution in the cell. The electrolytic bath 210 and the electrode bath 220 were connected via a salt bridge 240 and placed in a constant temperature bath 200 .

The counter electrode 202 was placed in the electrolytic bath 210 and immersed in the test solution. The reference electrode 203 was placed in the electrode bath 220 and immersed in the test solution. The temperature of the test solution was 40°C. After degassing the test solution by passing an inert gas through the electrolytic cell 210, the supply of the inert gas was stopped, and the test electrode 201 made of the welded test piece with a gap was placed in the electrolytic cell 210 and immersed in the test solution.

The potential difference between test electrode 201 and counter electrode 202 was held at 200 mV by potentiostat 250 . Corrosion current measurements were made by the Potentiostat 250 over 2000 hours and current-time polarization curves for the creviced specimens were obtained.

As shown in FIG. 1, when potassium nitrate was not added (0 M), the rise of the current value was confirmed 1 to 2 minutes after the voltage was applied. The reversal increase of the current value indicated by the arrow in the figure is due to the occurrence of crevice corrosion, and the subsequent gradual increase of the current value indicates that the crevice corrosion is progressing.

On the other hand, when the concentration of potassium nitrate was 0.1M, no rise in the current value was confirmed. It can be said that this result indicates that the addition of potassium nitrate to the test solution inhibited the crevice corrosion of S32750.

Table 1 shows the results of examining the concentrations of inorganic ions necessary for suppressing crevice corrosion in S32750, which is a duplex stainless steel, by corrosion tests. Table 2 shows the result of examining the concentration of inorganic ions necessary for suppressing crevice corrosion of SUS316L, which is an austenitic stainless steel, by a corrosion test.

The results shown in Tables 1 and 2 are obtained by preparing a welded test piece with a crevice (see FIG. 3) using a predetermined corrosion-resistant material, obtaining a current-time polarization curve using the measuring device shown in FIG. 4, and examining the occurrence and suppression of crevice corrosion. Required concentration means the minimum concentration of inhibitor required to inhibit crevice corrosion. This required concentration was obtained based on the presence or absence of a reversal increase in the current value (see arrow in FIG. 1) observed on the current-time polarization curve.

As an inhibitor for suppressing crevice corrosion, an aqueous solution of potassium nitrate or an aqueous solution of sodium molybdate was used. The corrosion test was conducted under various conditions by changing the chloride ion concentration (chlorine concentration) and pH of the test solution. The potential difference between the test electrode and the counter electrode was maintained at a constant voltage of 200 mV and corrosion current measurements were made over 2000 hours to determine the required concentration.

FIG. 5 is a diagram showing the relationship between the concentration of potassium nitrate and the concentration of chlorine required to suppress crevice corrosion of S32750. FIG. 6 is a diagram showing the relationship between the concentration of sodium molybdate and chlorine concentration required to suppress crevice corrosion of S32750. FIG. 7 is a diagram showing the relationship between the concentration of potassium nitrate and the concentration of chlorine required to suppress crevice corrosion of SUS316L. FIG. 8 is a diagram showing the relationship between the concentration of sodium molybdate and chlorine concentration required to suppress crevice corrosion of SUS316L.

As shown in Tables 1 and 2 and FIGS. 5 to 8, the minimum concentration (required concentration) required to suppress crevice corrosion varies depending on the type of metal material in which crevices are formed, the pH of the liquid, the concentration of chloride ions (chlorine concentration), and the type of inhibitor to be injected. The higher the concentration of chloride ions, the higher the required concentration of inhibitor. Further, in the pH range of 3.0 to 6.0, the required inhibitor concentration is higher than in the pH range of 6.0 to 8.0.

Conventionally, as a method for suppressing crevice corrosion, as described in Patent Document 1, there is known a method in which sulfate ions are present in a liquid that contacts a metal material. The inside of the crevice is positively charged, and the negative charge migrates into the crevice to neutralize the charge. However, the chloride ions that cause crevice corrosion have a negative charge, so the chloride ions move into the crevice and cause crevice corrosion. On the other hand, if anions other than chloride ions, such as sulfate ions, coexist, the amount of chloride ions moving into the crevices is relatively reduced, thereby suppressing crevice corrosion.

The inventors of the present invention conducted a corrosion test to investigate the concentration of various inorganic ions necessary to suppress crevice corrosion. As a result, nitrate ions and molybdate ions were found to be highly effective in suppressing crevice corrosion, but sulfate ions were not found to be sufficiently effective in suppressing crevice corrosion. Nitrate ions, which have a high oxidizing power, and molybdate ions, which are highly adsorbable and precipitable on surfaces, tend to form a passive film more easily than sulfate ions, so they are thought to be effective in suppressing crevice corrosion.

Therefore, as inhibitors to be injected into the liquid to be treated to suppress crevice corrosion of metal materials, liquids containing nitrate ions, liquids containing molybdate ions, nitrates, molybdates, and the like are preferable. Counter cations that form inhibitors include, for example, sodium ion, lithium ion, potassium ion, ammonium ion and the like, but are not particularly limited. As the counter cation, a sodium ion is preferable from the viewpoint of solubility, availability, and the like.

In addition, the concentration of chloride ions in the liquid to be treated that comes into contact with the metal material forming the structural member is preferably 20000 ppm or less, more preferably 5000 ppm or more and 20000 ppm or less. When the chloride ion concentration is 20000 ppm or less, crevice corrosion can be reliably suppressed with a small amount of inhibitor even when the pH of the liquid to be treated is as low as around 3.0. Also, if the chloride ion concentration is 5000 ppm or more, the susceptibility to crevice corrosion increases and the inhibitor is used more effectively.

A specific example of a liquid treatment system using an inhibitor for suppressing crevice corrosion will now be described.

FIG. 9 is a diagram showing the configuration of an adsorption system, which is an example of a liquid treatment system.
FIG. 9 illustrates a multi-stage adsorption system for treating contaminated water containing radioactive substances as an example of a liquid treatment system using an inhibitor. As shown in FIG. 9, the adsorption system 1 includes a supply pipe 5, a pH adjuster injection device 10, a plurality of adsorption towers 11, 12, 13, 14, an inhibitor injection device 20, a sensor unit 30, and a removal tower (removal device) 40.

The adsorption system 1 is a device that separates and removes radioactive substances contained in contaminated water (liquid to be treated) by adsorption. As the liquid to be treated, contaminated water generated in a nuclear reactor facility, contaminated water generated during decontamination, and the like are treated. Contaminated water is subjected to pretreatment such as filtration, carbonate precipitation, iron coprecipitation, etc., and then sent to adsorption tower 11 through supply pipe 5. A plurality of adsorption towers 11 to 14 provided in series sequentially perform adsorption treatment and recover the treated liquid.

Each of the adsorption towers 11-14 incorporates an adsorbent for removing predetermined radionuclides. As the adsorbent, an appropriate adsorbent is used according to the radionuclide to be removed. Radionuclides to be removed by the adsorption system 1 include Cs-134, Cs-137, Sr-89, Sr-90, I-129, Co-60, Sb-125, Ru-106, H-3(T), and the like.

Specific examples of adsorbents include cation exchange resins, anion exchange resins, chelate resins, zeolites, activated carbon, magnesium oxide, titanium oxide, silica, titanates, silicotitanates, iron hydroxides, and ferrocyanic compounds.

The adsorption towers 11 to 14 preferably include at least a cation exchange type adsorbent such as a cation exchange resin or a chelate resin. When such an adsorbent is provided, the liquid to be treated is adjusted to acidic conditions, so the susceptibility to crevice corrosion increases and the inhibitor is used more effectively.

Specific examples of the arrangement of the adsorption towers 11 to 14 include a chelate resin in the first adsorption tower 11, magnesium oxide in the second adsorption tower 12, ion exchange resin in the third adsorption tower 13, and zeolite in the fourth adsorption tower 14. According to the chelate resin, Mn, Fe, Co, etc. are captured by complexation. Magnesium oxide captures tritium (T) and the like through a hydration reaction. Ion exchange resins trap various ions such as Ce and Sr by ion exchange. Zeolite captures Ce, Sr, I, etc. by molecular sieve/ion exchange.

In the adsorption system 1, the supply pipe 5 upstream of the adsorption tower 11 is equipped with a pH adjuster injection device 10 for injecting a pH adjuster for lowering the pH of the liquid to be treated. The pH adjuster injection device 10 includes a tank for storing the pH adjuster, a pump for injecting the pH adjuster into the liquid to be treated, and the like. The liquid to be treated is adjusted to a pH suitable for adsorption treatment by injecting a pH adjuster. For example, after being adjusted to acidic conditions such as pH 3.5 necessary for the reaction of the chelate resin, it is sent to adsorption towers 11-14.

The adsorption towers provided in the adsorption system 1, the built-in components of the adsorption towers, and the pipes connected to the adsorption towers are mainly made of metal materials. Stainless steel is often used as the metal material, and duplex stainless steel and austenitic stainless steel, which are excellent in corrosion resistance, are generally used.

The inner surface of the wall portion of the adsorption tower provided in the adsorption system 1, the surface of the support portion of the adsorbent, the surface of the partition portion in the adsorption tower, the inner surface of the pipe connected to the adsorption tower, etc. are wetted portions that come into contact with the liquid to be treated. Therefore, corrosion of metal materials should be prevented. In particular, when the liquid to be treated is adjusted to acidic conditions, when the concentration of chloride ions in the liquid to be treated is high, or when the liquid to be treated contains radioactive substances, the susceptibility of metal materials to crevice corrosion increases, so there is concern about the occurrence and progression of crevice corrosion in the metal materials that make up the wetted parts.

Therefore, the adsorption system 1 is equipped with an inhibitor injection device 20 in the supply pipe 10 upstream of the adsorption tower 11 for injecting an inhibitor into the liquid to be treated for suppressing crevice corrosion of the metal material. The inhibitor injection device 20 can include a tank for storing the inhibitor, a pump for injecting the inhibitor into the liquid to be treated, and the like. After being injected with an inhibitor, the liquid to be treated is sent toward the adsorption towers 11 to 14 to suppress the occurrence and progression of crevice corrosion accompanying the passage of the liquid to be treated.

In FIG. 9, the inhibitor injection device 20 is provided in the supply pipe 10 upstream of the adsorption tower 11, but the inhibitor injection device 20 may be provided in a pipe connecting the adsorption towers 11 to 14, a pipe downstream of the adsorption tower 14, or inside the adsorption towers 11 to 14.

9, the inhibitor injection device 20 is provided on the upstream side of the pH adjuster injection device 10 in the supply pipe 10, but the inhibitor injection device 20 may be provided on the downstream side of the pH adjuster injection device 10. However, when a pH adjuster that lowers the pH is injected into the liquid to be treated, the occurrence and progress of crevice corrosion is accelerated.

In the adsorption system 1, in the supply pipe 5 upstream of the adsorption tower 11, a sensor unit 30 that measures the properties of the liquid to be treated can be provided in a section downstream of the chemical injection position of the inhibitor and the chemical injection position of the pH adjuster. The sensor unit 30 may include a pH sensor that measures the pH of the liquid to be treated, a chlorine sensor that measures the concentration of chloride ions contained in the liquid to be treated, an ion sensor that measures the concentration of the inhibitor injected into the liquid to be treated, and the like.

As the chlorine sensor or the ion sensor, for example, an ion sensor equipped with a diaphragm-type ion selective electrode can be used according to the ion species to be measured. However, depending on the ionic strength of the liquid to be treated and the concentration of interfering ions, it may be difficult to accurately measure the concentration. In such a case, it is possible to use a method of calculation using a database that reflects an error range obtained in advance, a method of correction using a selection coefficient, or the like.

In the inhibitor injection device 20, the amount of inhibitor injected into the liquid to be treated may be controlled to be constant (constant flow rate) or variably. Further, the inhibitor injection device 20 may continuously or intermittently inject the inhibitor into the liquid to be treated. The inhibitor is usually injected into the liquid to be treated during adsorption treatment, but may be injected during maintenance of the adsorption system 1, for example, when water is passed through the adsorption towers 11 to 14 for removing residual liquid.

The inhibitor injection device 20 is preferably controlled to inject a predetermined amount of inhibitor based on the pH and chloride ion concentration of the liquid to be treated by measuring the liquid to be treated with the sensor unit 30. Measurement by the sensor unit 30 can be performed at arbitrary sampling intervals.

The injection amount of the inhibitor can be controlled according to the result of measurement by the sensor unit 30 so that the required concentration of the inhibitor is present in the liquid to be treated. A database containing data on the necessary concentration of the inhibitor for each chloride ion concentration, a relational expression showing the quantitative relationship between the necessary concentration of the inhibitor and the chloride ion concentration, and the like are prepared by performing corrosion tests in advance, and these can be used to variably control the injection amount.

By controlling the inhibitor injection device 20 to inject a predetermined amount based on the pH and the concentration of chloride ions, the amount of inhibitor to be added can be suppressed while reliably suppressing the occurrence and progress of crevice corrosion with a small amount of inhibitor. Therefore, the cost required to prevent crevice corrosion can be reduced. In addition, since the amount of the inhibitor component mixed in the liquid to be treated is reduced, the load on the adsorption tower and the removal tower is reduced. Moreover, when the liquid to be treated is a liquid containing radioactive substances, the final disposal amount of radioactive substances can be reduced.

Specifically, when the metal material of the liquid contacting portion that contacts the liquid to be treated is duplex stainless steel, and the liquid to be treated has a pH of less than 6.0, it is preferable that the ratio of the molar concentration of nitrate ions and the molar concentrations of chloride ions is adjusted to 0.16 or more, or the ratio of the molar concentrations of molybdate ions to the chloride ions is adjusted to 0.1 or more.

In such a case, from the viewpoint of suppressing the injection amount of the inhibitor and the corrosion of the metal material, the ratio between the molar concentration of nitrate ions and the molar concentrations of chloride ions and the molar concentration of molybdate ions and the molar concentrations of chloride ions are more preferably less than 1.0, more preferably less than 0.5, and even more preferably less than 0.2.

Further, when the metal material of the wetted part that contacts the liquid to be treated is duplex stainless steel and the pH of the liquid to be treated is 6.0 or more and 8.0 or less, it is preferable that the ratio of the molar concentration of nitrate ions and the molar concentrations of chloride ions is adjusted to 0.02 or more, or the ratio of the molar concentrations of molybdate ions and chloride ions is adjusted to 0.007 or more.

In such a case, from the viewpoint of suppressing the injection amount of the inhibitor and the corrosion of the metal material, the ratio between the molar concentration of nitrate ions and the molar concentrations of chloride ions and the ratio between the molar concentrations of molybdate ions and the chloride ions are more preferably less than 1.0, more preferably less than 0.5, further preferably less than 0.2, further preferably less than 0.1, and even more preferably less than 0.05.

On the other hand, when the metal material of the liquid contacting portion that contacts the liquid to be treated is austenitic stainless steel, and the liquid to be treated has a pH of less than 6.0, it is preferable that the ratio of the molar concentration of nitrate ions and the molar concentrations of chloride ions is adjusted to 0.46 or more, or the ratio of the molar concentrations of molybdate ions to the chloride ions is adjusted to 0.2 or more.

In such a case, from the viewpoint of suppressing the injection amount of the inhibitor and the corrosion of the metal material, the ratio between the molar concentration of nitrate ions and the molar concentrations of chloride ions, and the ratio between the molar concentrations of molybdate ions and chloride ions, is more preferably less than 2.0, more preferably less than 1.5, and even more preferably less than 1.0.

Further, when the metal material of the liquid-contacting portion that contacts the liquid to be treated is austenitic stainless steel, and the liquid to be treated has a pH of 6.0 or more and 8.0 or less, it is preferable that the ratio of the molar concentration of nitrate ions and the molar concentrations of chloride ions is adjusted to 0.2 or more, or the ratio of the molar concentrations of molybdate ions to the chloride ions is adjusted to 0.1 or more.

In such a case, from the viewpoint of suppressing the injection amount of the inhibitor, the ratio of the molar concentration of nitrate ions to the molar concentration of chloride ions and the ratio of the molar concentrations of molybdate ions to the chloride ions are more preferably less than 2.0, more preferably less than 1.0, further preferably less than 0.5, and even more preferably less than 0.2.

In the adsorption system 1, a removal tower 40 can be provided downstream of the adsorption towers 11 to 14 in order to remove the components of the injected inhibitor from the liquid to be treated into which the inhibitor has been injected. When the inhibitor is injected into the liquid to be treated, the concentrations of anions, cations, and the like, which are components of the inhibitor, increase. When the removal tower 40 is provided, even if such inhibitor components are not separated and removed in the adsorption towers 11 to 14, the inhibitor components can be separated and removed before the treatment liquid is discharged.

As the removal column 40, when nitrate ions are used as a component of the inhibitor, an apparatus using an ion exchange method, an adsorption method, a membrane separation method, a catalytic desorption method, or the like can be used. As the ion exchanger, a short fiber resin having highly hydrophobic ion exchange groups is preferably used from the viewpoint of ion selectivity and reaction efficiency. Examples of adsorbents that can be used include zeolite and activated carbon. Nitrate ions may be treated after being reduced to ammoniacal nitrogen with a platinum catalyst, a copper-supported catalyst, low-crystalline iron powder, or the like.

As the removal tower 40, when molybdate ion is used as a component of the inhibitor, an apparatus using an ion exchange method, an adsorption method, a membrane separation method, or the like can be used. As the ion exchanger, for example, a strongly basic anion exchange resin having a quaternary ammonium or the like as an exchange group, a weakly basic anion exchange resin having a primary or secondary ammonium or the like as an exchange group, a chelate-type anion exchange resin having a polyamine or the like as an exchange group, or the like can be used.

According to the adsorption system 1 described above, an inhibitor for suppressing crevice corrosion can be injected into the liquid to be treated sent to the adsorption tower. Therefore, even if the liquid to be treated that is sent to the adsorption tower or the like is adjusted to have an acidic condition, it is possible to suppress the occurrence and progress of crevice corrosion in the metal material that constitutes the liquid contact portion. In addition, since crevice corrosion is suppressed, even if tensile stress or the like is applied, stress corrosion cracking is less likely to occur. Damage to devices and equipment in the system, leakage of the liquid to be treated, etc. can be reduced over a long period of time, and repair and replacement of devices and equipment can be reduced. Therefore, it is possible to provide a long-life and highly reliable adsorption system in which the structural material of the wetted portion that contacts the liquid to be treated is less likely to cause localized corrosion. Since localized corrosion is suppressed by the inhibitor, extremely high corrosion resistance is no longer required for structural materials, and general-purpose metal materials can be used, thereby reducing costs.

FIG. 10 is a diagram showing the configuration of a waste liquid treatment system, which is an example of a liquid treatment system.
FIG. 10 illustrates a waste liquid treatment system for treating radioactive waste liquid as an example of a liquid treatment system using an inhibitor. As shown in FIG. 10, the waste liquid treatment system 2 includes an oil removal device 21, a filtration device 22, a first evaporative concentration device 23, an adsorption device 24, a storage tank 25, a chlorine removal device 26, a chlorine recovery device 27, a second evaporative concentration device 28, a pH adjuster injection device 10, an inhibitor injection device 20, a sensor unit 30, and a removal tower (removal device) 40.

The liquid waste treatment system 2 is a device that separates radioactive substances contained in a radioactive liquid waste (liquid to be treated), concentrates, reduces the volume of, and reduces the dose of the radioactive liquid waste to recover it. As the radioactive liquid waste, high-level radioactive liquid waste generated in a nuclear reactor facility, liquid waste generated by cleaning contaminated soil contaminated with radioactive substances, and the like are treated. The radioactive waste liquid is sequentially sent to the oil removal device 21, the filtration device 22, the first evaporative concentration device 23, the chlorine removal device 26, the removal tower 40, and the second evaporative concentration device 28, where reusable substances such as water and chlorine are recovered and the volume is reduced to recover a concentrated waste liquid in which radioactive substances with low volatility are concentrated.

The oil removal device 21 separates and removes oil, coarse floating matter, suspended matter, and the like contained in the liquid to be treated. As the oil removal device 21, for example, a pressurized flotation device, an oil-water separation separator, or the like is used. The liquid to be treated from which some radioactive substances have been separated and removed together with oil and the like is sent to the filtering device 22 .

The filtering device 22 separates and removes minute floating matter, suspended matter, etc. remaining in the liquid to be treated by the principle of filtration. As the filtering device 22, a membrane separating device, a sand filtering device, or the like is used. The liquid to be treated from which a part of the radioactive substances has been separated and removed together with fine suspended solids and suspended solids is sent to the first evaporative concentration device 23 .

The first evaporative concentration device 23 evaporates the liquid to be treated containing radioactive substances, reduces the volume of the liquid to be treated, and concentrates the radioactive substances with low volatility in the liquid to be treated. Since most of the radioactive substances are non-volatile, they remain in the liquid phase and are concentrated even if the liquid to be treated evaporates. As the evaporative concentration device, for example, a vapor compression device or the like is used. The vapor evaporated from the liquid to be treated is condensed into a condensed liquid (condensed water), which is sent to the adsorption device 24 . On the other hand, the liquid to be treated in which radioactive substances are concentrated is sent to the storage tank 25 .

The adsorption device 25 separates and removes radioactive substances contained in the condensate separated from the liquid to be treated. As the adsorption device 25, an adsorption material such as a cation exchange resin, anion exchange resin, chelate resin, zeolite, activated carbon, magnesium oxide, titanium oxide, silica, titanate, silicotitanate, iron hydroxide, ferrocyanic compound, etc., or an apparatus having the same configuration as the adsorption system 1 is used. The condensate from which radioactive substances have been separated and removed is discharged into the ocean or reused.

The storage tank 25 temporarily stores the concentrated liquid to be processed. The waste liquid treatment system 2 is equipped with two-stage evaporative concentration devices 23 and 28 . The liquid to be treated whose volume has been reduced by the first evaporative concentration device 23 of the first stage is temporarily stored in the storage tank 25, and is discharged toward the second evaporative concentration device 28 at a predetermined stage, where it is further concentrated and reduced in volume. The liquid to be treated stored in the storage tank 25 is first sent to the chlorine removing device 26 .

The chlorine remover 26 separates and removes chloride ions contained in the liquid to be treated. As the chlorine removing device 26, for example, an electrolytic device or the like is used. In the electrolytic device, the liquid to be treated containing chloride ions is electrolyzed so as to generate hydrogen gas and hypochlorous acid. Hypochlorous acid is conditioned to acidic conditions by acid injection and converted to chlorine gas. Chlorine gas is sent to the chlorine recovery device 27 . On the other hand, the liquid to be treated from which the chlorine content has been separated and removed is sent to the removal tower 40 and sent from the removal tower 40 to the second evaporative concentration device 28 .

The chlorine recovery device 27 fixes and recovers the chlorine gas, which is the chlorine content separated from the liquid to be treated. Chlorine gas is recovered by, for example, a method of converting it into hydrochloric acid in a washing tower or the like, or a method of converting it into chloride, hypochlorite, or the like by precipitating it with an alkaline solution such as sodium hydroxide. Chloride ions remaining in the chlorine remover 26 are recovered by a method of converting them into silver chloride by precipitating them with silver nitrate or silver sulfate.

The second evaporative concentration device 28, like the first evaporative concentration device 23, evaporates the liquid to be treated containing radioactive substances, reduces the volume of the liquid to be treated, and further concentrates the radioactive substances with low volatility. As the evaporative concentration device, a vacuum evaporative compression type device or the like is used. The liquid to be treated in which radioactive substances are concentrated is collected as a concentrated waste liquid, solidified and stored.

In the waste liquid treatment system 2, upstream of the chlorine remover 26, a pH adjuster injection device 10 for injecting a pH adjuster for lowering the pH of the liquid to be treated is provided. The pH adjuster injection device 10 includes a tank for storing the pH adjuster, a pump for injecting the pH adjuster into the liquid to be treated, and the like. The liquid to be treated is injected with a pH adjusting agent to adjust the pH to a suitable level for converting the chlorine contained in the liquid to be treated into chlorine gas.

Each device/equipment provided in the waste liquid treatment system 2, internal components of the device/equipment, and piping connected to the device/equipment are mainly formed of metal materials. Stainless steel is often used as the metal material, and duplex stainless steel and austenitic stainless steel, which are excellent in corrosion resistance, are generally used.

The inner surface of the wall of each device/equipment provided in the waste liquid treatment system 2, the surface of the internal parts of the device/equipment, the inner surface of the piping connected to the device/equipment, etc. are wetted parts that come into contact with the liquid to be treated, and therefore are parts that should be protected from corrosion of metal materials. In particular, when the liquid to be treated is adjusted to acidic conditions, when the concentration of chloride ions in the liquid to be treated is high, or when the liquid to be treated contains radioactive substances, the susceptibility of metal materials to crevice corrosion increases, so there is concern about the occurrence and progression of crevice corrosion in the metal materials that make up the wetted parts.

Therefore, in the waste liquid treatment system 2, an inhibitor injection device 20 for injecting an inhibitor for suppressing crevice corrosion of metal materials into the liquid to be treated is provided in a section downstream of the first evaporative concentration device 23 and upstream of the storage tank 25. The inhibitor injection device 20 can include a tank for storing the inhibitor, a pump for injecting the inhibitor into the liquid to be treated, and the like. After being injected with an inhibitor, the liquid to be treated is sent toward the second evaporative concentration device 28 to suppress the occurrence and progression of crevice corrosion accompanying the passage of the liquid to be treated.

As shown in FIG. 10, when the inhibitor injection device 20 is provided in a section downstream of the first evaporative concentration device 23 and upstream of the storage tank 25, the occurrence and progress of crevice corrosion can be suppressed downstream of the first evaporative concentration device 23 including the storage tank 25 even when the radioactive waste liquid containing chloride ions is concentrated and the concentration of chloride ions in the liquid to be treated increases.

As shown in FIG. 10 , the pH adjuster injection device 10 is preferably provided downstream of the storage tank 25 and upstream of the chlorine removal device 26 . According to this arrangement, even when chlorine or the like is used as a pH adjuster, it is possible to prevent the inner surface of the wall of the storage tank 25, the surface of the contents of the storage tank 25, and the like from being exposed to high-concentration chloride ions and low-pH acidic conditions while the concentrated liquid to be treated is being stored. Therefore, even when the concentrated liquid to be treated is stored for a long period of time, it is possible to suppress the occurrence and progression of crevice corrosion in the storage tank 25 .

In the waste liquid treatment system 2, among the sections downstream of the first evaporative concentration device 23 and upstream of the chlorine removal device 26, a section downstream of the chemical injection position of the inhibitor and the chemical injection position of the pH adjuster can be provided with a sensor unit 30 that measures the properties of the liquid to be treated. Similar to the adsorption system 1, the sensor unit 30 can include a pH sensor, a chlorine sensor, an ion sensor, and the like.

In the inhibitor injection device 20, the amount of inhibitor injected into the liquid to be treated may be controlled to be constant (constant flow rate) or variably. Further, the inhibitor injection device 20 may continuously or intermittently inject the inhibitor into the liquid to be treated.

The inhibitor injection device 20 is preferably controlled to inject a predetermined amount of inhibitor based on the pH and chloride ion concentration of the liquid to be treated by measuring the liquid to be treated with the sensor unit 30. Measurement by the sensor unit 30 can be performed at arbitrary sampling intervals. The injection amount of the inhibitor can be controlled according to the result of measurement by the sensor unit 30 as in the adsorption system 1 .

In the waste liquid treatment system 2, a removal tower 40 can be provided in a section downstream of the inhibitor chemical injection position and the pH adjuster chemical injection position in order to remove the injected inhibitor component from the liquid to be treated into which the inhibitor has been injected, as in the adsorption system 1. By providing the removal tower 40, such inhibitor components can be separated and removed from the concentrated liquid to be treated.

According to the waste liquid treatment system 2 described above, an inhibitor for suppressing crevice corrosion can be injected into the evaporated and concentrated liquid to be treated. Therefore, even if radioactive waste containing chloride ions is subjected to treatment due to the chlorination of radioactive substances that generate radioactive waste, the use of seawater in nuclear reactor facilities, etc., and the concentration of chloride ions in the liquid to be treated increases due to concentration, or the liquid to be treated is adjusted to be under acidic conditions, the occurrence and progress of crevice corrosion can be suppressed for the metal materials that constitute the liquid contact parts. In addition, since crevice corrosion is suppressed, even if tensile stress or the like is applied, stress corrosion cracking is less likely to occur. Damage to devices and equipment in the system, leakage of the liquid to be treated, etc. can be reduced over a long period of time, and repair and replacement of devices and equipment can be reduced. Therefore, it is possible to provide a liquid treatment system having a long service life and high reliability, in which the structural material of the liquid contacting portion that is in contact with the liquid to be treated is less likely to be locally corroded. Since localized corrosion is suppressed by the inhibitor, extremely high corrosion resistance is no longer required for structural materials, and general-purpose metal materials can be used, thereby reducing costs.

Next, a crevice corrosion monitor device used for monitoring crevice corrosion of metal materials will be described with reference to the drawings.

FIG. 11 is a diagram showing the configuration of a crevice corrosion monitor used for monitoring crevice corrosion.
As shown in FIG. 11 , the crevice corrosion monitor device 300 includes a crevice metal electrode 310 , a counter electrode 320 , a reference electrode 330 and a potentiostat 340 .

The crevice corrosion monitor device 300 is a device for detecting crevice corrosion occurring in a metal material forming a liquid-contacting portion by means of a corrosion current flowing through a crevice metal electrode 310 .

The crevice corrosion monitor device 300 can be installed on liquid-contacting parts in liquid treatment systems such as the adsorption system 1 and the waste liquid treatment system 2, i.e., the inner surface of the walls of each device/equipment, the surface of the built-in parts of the equipment/equipment, the inner surface of pipes connected to the equipment/equipment, and the like.

As shown in FIG. 11, the gapped metal electrode 310, the counter electrode 320, and the reference electrode 330 are fixed so as to pass through the structural material 301 forming the wetted portion. The tip side of each electrode is exposed to the internal space 302 where the liquid to be treated exists and is supported in contact with the liquid to be treated. The base end side of each electrode is fixed in the external space 303 of the structural member 301 with a fastener 350 such as a hexagon bolt nut. An insulating material (not shown) electrically insulates each electrode from the structural member 301 and the fastener 350 .

As the gapped metal electrode 310, a metal electrode made of the same material as the metal material to be monitored is used. A gap is formed between the metal electrodes by attaching a gap forming material 351 . The tip end side to which the crevice forming member 351 is attached is exposed to the internal space 302 of the structural member 301 and brought into contact with the liquid to be treated that causes crevice corrosion.

An appropriate member can be used as the gap forming member 351 . For example, an insulating material such as epoxy resin, vinyl chloride resin, or silicone resin can be used in the form of covering the surface of the electrode to form the gap. Alternatively, a titanium bolt nut, a titanium washer, or the like can be used in the form of being fastened to the surface of the electrode to form the gap. Alternatively, a test piece with gaps prepared by the same method as in FIG. 3 may be used.

As the counter electrode 320, for example, a platinum electrode can be used. As the reference electrode 330, for example, a silver-silver chloride electrode can be used. The tip of the counter electrode 320 and the tip of the reference electrode 330 provided with the liquid junction 352 are exposed to the internal space 302 of the structural member 301 and brought into contact with the liquid to be treated that causes crevice corrosion.

The potentiostat 340 maintains the electrode potential of the gapped metal electrode 310 and measures the corrosion current flowing between the gapped metal electrode 310 and the counter electrode 320 by the current measurement function. A signal representing the value of the current flowing between the electrodes can be output to, for example, a controller that controls the inhibitor injection device 20 described above. When the value of the current flowing between the electrodes exceeds a predetermined threshold, it is assumed that crevice corrosion has occurred, and injection of the inhibitor into the liquid to be treated can be initiated.

As the potentiostat 340, either a grounded counter electrode type device or a grounded working electrode type device can be used, but the grounded counter electrode type device is preferable. If it is a counter electrode grounding type device, the correct potential can be measured without being significantly affected by the grounding/insulation state of the metal electrode 310 with gap and the system circuit.

According to such a crevice corrosion monitor device 300, crevice corrosion occurring in the structural material constituting the wetted portion can be easily detected from changes in the corrosion current. Since it can be provided with a simple structure on the wetted parts in the liquid treatment system such as the adsorption system 1 and the waste liquid treatment system 2, that is, the inner surface of the wall of each device / equipment, the surface of the internal part of the device / equipment, the inner surface of the piping connected to the equipment / equipment, etc. Therefore, it is possible to prevent the components of the inhibitor from being mixed into the liquid to be treated and to save the inhibitor.

Next, the results of a corrosion test of the structural material that constitutes the wetted portion in an adsorption system, which is an example of a liquid treatment system, will be shown.

FIG. 12 is a diagram showing changes over time in the corrosion current, the concentration of nitrate ions, the concentration of chloride ions contained in the liquid to be treated, and the pH of the liquid to be treated when potassium nitrate is injected into the liquid to be treated in the adsorption system.
FIG. 12 shows changes over time in the corrosion current, nitrate ion concentration, chloride ion concentration, and pH when hydrochloric acid as a pH adjuster and a solution of potassium nitrate as an inhibitor for suppressing crevice corrosion are injected in the adsorption system shown in FIG.

The corrosion current is the current that flows between the creviced metal electrode and the counter electrode when a crevice corrosion monitor device (see FIG. 11) is installed in the adsorption system and the creviced metal electrode is polarized to 200 mV with respect to the reference electrode and held. A metal electrode formed of S32750 was used as the metal electrode with a gap.

As shown in FIG. 12, the concentration of chloride ions in the liquid to be treated in the initial period remained around 20000 ppm. Further, the pH of the liquid to be treated remained around 3.5. A relatively large current of 5 to 7 mA was measured by the crevice corrosion monitor until the third day of the corrosion test. It is believed that crevice corrosion of S32750 progressed under acidic conditions with a high chlorine concentration until the third day, and a corrosion current was observed.

Subsequently, on the third day, the injection of potassium nitrate was started and the concentration of nitrate ion was adjusted to 0.1M. As a result, the current value began to decrease, and became approximately 0 mA after the fifth day. From this result, it can be seen that the progress of crevice corrosion of S32750 was stopped by the injection of potassium nitrate. On the 9th and 10th days, when the concentration of chloride ions decreased to around 5000 ppm, the concentration of nitrate ions was gradually lowered to the required concentration (see Table 1).

FIG. 13 is a diagram showing changes over time in the corrosion current, the concentration of sulfate ions, the concentration of chloride ions contained in the liquid to be treated, and the pH of the liquid to be treated when sodium sulfate is injected into the liquid to be treated in the adsorption system.
FIG. 13 shows changes over time in the corrosion current, the concentration of sulfate ions, the concentration of chloride ions, and the pH when hydrochloric acid as a pH adjuster and a solution of sodium sulfate as an inhibitor for suppressing crevice corrosion are injected in the adsorption system shown in FIG. Other conditions are the same as in the case of injecting a solution of potassium nitrate as an inhibitor.

As shown in FIG. 13, the concentration of chloride ions in the liquid to be treated in the initial period remained around 20000 ppm. Further, the pH of the liquid to be treated remained around 3.5. A relatively large current of 5 to 7 mA was measured by the crevice corrosion monitor until the third day of the corrosion test. It is believed that crevice corrosion of S32750 progressed under acidic conditions with a high chlorine concentration until the third day, and a corrosion current was observed.

Subsequently, on the third day, injection of sodium sulfate was started and the concentration of sulfate ions was adjusted to 0.1M. As a result, no decrease in current value was measured. On the 9th and 10th days, when the chloride ion concentration decreased to around 5000 ppm, the sulfate ion concentration was increased to 0.5 M, but no decrease in the current value was still measured. From this result, it can be seen that the progress of crevice corrosion of S32750 is not inhibited by sodium sulfate under acidic conditions.

FIG. 14 is a diagram showing changes over time in the corrosion current, the concentration of molybdate ions, the concentration of chloride ions contained in the liquid to be treated, and the pH of the liquid to be treated when sodium molybdate is injected into the liquid to be treated in the adsorption system. Other conditions are the same as in the case of injecting a solution of potassium nitrate as an inhibitor.

As shown in FIG. 14, the concentration of chloride ions in the liquid to be treated in the initial stage changed around 180,000 to 20,000 ppm. Further, the initial pH of the liquid to be treated remained around 3.5. Until the third day after starting the corrosion test, a relatively large current of around 5 to 7 mA was measured by the crevice corrosion monitor. It is believed that crevice corrosion of S32750 progressed under acidic conditions with a high chlorine concentration until the third day, and a corrosion current was observed.

Subsequently, on the 30th day, injection of sodium molybdate was started and the concentration of molybdate ions was adjusted to 0.05M. As a result, the current value began to decrease, and reached approximately 0 mA after the 50th day. From this result, it can be seen that the progress of crevice corrosion of S32750 was stopped by the injection of sodium molybdate. On the 60th day, when the injection of hydrochloric acid was stopped and the pH increased, the concentration of molybdate ions was decreased to 1/10. Thereafter, on the 100th to 110th days, when hydrochloric acid was injected again to lower the pH, an increase in the current value was measured, and crevice corrosion continued to occur and progress. On the 130th to 140th days, when the chloride ion concentration was lowered to around 5000 ppm, it was confirmed that the current value decreased again and progress of crevice corrosion stopped.

Although the present invention has been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. For example, the present invention is not necessarily limited to having all the configurations included in the above embodiments. A part of the configuration of an embodiment can be replaced with another configuration, a part of the configuration of an embodiment can be added to another form, or a part of the configuration of a certain embodiment can be omitted.

For example, the inhibitor injection device 20 is provided at a predetermined position in the adsorption system 1 or the waste liquid treatment system 2, but the inhibitor injection device can be provided at an appropriate location where it is necessary to suppress crevice corrosion of metal materials, such as the inside of various treatment devices that physically or chemically treat the liquid to be treated, and piping that supplies the liquid to be treated to the treatment device, which is provided in the liquid treatment system.

In addition, in the adsorption system 1, a total of four stages of adsorption towers 11 to 14 are provided in series, but the adsorption system that removes substances contained in the liquid to be treated by adsorption is not particularly limited in the number and type of adsorption towers. Moreover, the arrangement order of the adsorption towers and the number of towers per stage are not particularly limited. The adsorption towers can be arranged in multiple stages for each type of adsorbent, and can be arranged in an appropriate order according to the object to be removed.

In the waste liquid treatment system 2, the oil removal device 21, the filtration device 22, the first evaporative concentration device 23, the adsorption device 24, the storage tank 25, the chlorine removal device 26, the chlorine recovery device 27, and the second evaporative concentration device 28 are provided. Also, the order of arrangement of the adsorption towers and the number of towers per stage are not particularly limited. As long as an evaporative concentration device for concentrating the liquid to be treated is provided, the evaporative concentration device may be multi-staged to an appropriate number of stages of two or more, and the separation and recovery of radioactive substances may be added or omitted.

1 Adsorption system (liquid treatment system)
2 Waste liquid treatment system (liquid treatment system)
5 supply pipe 10 pH adjuster injector (pH adjuster)
11 First adsorption tower 12 Second adsorption tower 13 Third adsorption tower 14 Fourth adsorption tower 20 Inhibitor injection device 21 Oil removal device 22 Filtration device 23 First evaporative concentration device 24 Adsorption device 25 Storage tank 26 Chlorine removal device 27 Chlorine recovery device 28 Second evaporative concentration device 30 Sensor unit 40 Removal tower (removal device)
100 Welded test piece 100a Steel plate 100b Steel plate 120 Welded part 130 Impression material 150 Test piece with crevice 200 Constant temperature bath 201 Test electrode 202 Counter electrode 203 Reference electrode 210 Electrolytic bath 220 Electrode bath 230 Vent pipe 240 Salt bridge 250 Potentiostat 300 Crevice corrosion monitor device 301 Structural material 302 Internal space 303 Outside Space 310 Metal electrode with gap 320 Counter electrode 330 Reference electrode 340 Potentiostat 350 Fastener 351 gap forming material 352 Liquid junction

Claims (13)

A liquid treatment system for adjusting the property, state, or amount of components of a liquid to be treated, wherein at least a portion of a liquid contacting portion that contacts the liquid to be treated is made of a metal material, and includes an inhibitor injection device for injecting an inhibitor for suppressing crevice corrosion of the metal material into the liquid to be treated, and a pH adjuster injection device for injecting a pH adjuster for lowering the pH of the liquid to be treated, wherein the liquid to be treated is a liquid containing chloride ions, and the inhibitor is molybdic acid. A liquid containing ions,
The metal material is duplex stainless steel,
The liquid to be treated into which the inhibitor is injected is
A liquid treatment system having a pH of less than 6.0 and a molar concentration ratio of molybdate ions to chloride ions adjusted to 0.1 or greater. A liquid treatment system for adjusting the property, state, or amount of components of a liquid to be treated, wherein at least a portion of a liquid contacting portion that contacts the liquid to be treated is made of a metal material, and includes an inhibitor injection device for injecting an inhibitor for suppressing crevice corrosion of the metal material into the liquid to be treated, and a pH adjuster injection device for injecting a pH adjuster for lowering the pH of the liquid to be treated, wherein the liquid to be treated is a liquid containing chloride ions, and the inhibitor is molybdic acid. A liquid containing ions,
The metal material is duplex stainless steel,
The liquid to be treated into which the inhibitor is injected is
A liquid treatment system having a pH of 6.0 or more and 8.0 or less, and a ratio of a molar concentration of molybdate ions to a molar concentration of chloride ions adjusted to 0.007 or more. A liquid treatment system for adjusting the property, state, or amount of components of a liquid to be treated, wherein at least a portion of a liquid contacting portion that contacts the liquid to be treated is made of a metal material, and includes an inhibitor injection device for injecting an inhibitor for suppressing crevice corrosion of the metal material into the liquid to be treated, and a pH adjuster injection device for injecting a pH adjuster for lowering the pH of the liquid to be treated, wherein the liquid to be treated is a liquid containing chloride ions, and the inhibitor is molybdic acid. A liquid containing ions,
The metal material is austenitic stainless steel,
The liquid to be treated into which the inhibitor is injected is
A liquid treatment system wherein the pH is less than 6.0 and the ratio of the molar concentration of molybdate ions to the molar concentrations of chloride ions is adjusted to 0.2 or more. A liquid treatment system for adjusting the property, state, or amount of components of a liquid to be treated, wherein at least a portion of a liquid contacting portion that contacts the liquid to be treated is made of a metal material, and includes an inhibitor injection device for injecting an inhibitor for suppressing crevice corrosion of the metal material into the liquid to be treated, and a pH adjuster injection device for injecting a pH adjuster for lowering the pH of the liquid to be treated, wherein the liquid to be treated is a liquid containing chloride ions, and the inhibitor is molybdic acid. A liquid containing ions,
The metal material is austenitic stainless steel,
The liquid to be treated into which the inhibitor is injected is
A liquid treatment system having a pH of 6.0 or more and 8.0 or less, and a ratio of a molar concentration of molybdate ions to a molar concentration of chloride ions adjusted to 0.1 or more. A liquid treatment system according to any one of claims 1 to 4,
The liquid treatment system, wherein the liquid to be treated is a liquid containing a radioactive substance. A liquid treatment system according to any one of claims 1 to 4,
A liquid treatment system comprising a removal device for removing a component of the inhibitor injected from the liquid to be treated. A liquid treatment system according to any one of claims 1 to 4,
a pH sensor for measuring the pH of the liquid to be treated;
a chlorine sensor for measuring the concentration of chloride ions contained in the liquid to be treated;
The liquid treatment system, wherein the inhibitor injector injects a predetermined amount of the inhibitor based on the pH and chloride ion concentration of the liquid to be treated. A liquid treatment system according to any one of claims 1 to 4,
The liquid treatment system comprises an evaporative concentration device for concentrating the liquid to be treated,
The inhibitor injection device injects the inhibitor into the liquid to be treated that has been concentrated by the evaporative concentration device,
The pH adjuster injection device is a liquid treatment system for injecting the pH adjuster into the liquid to be treated into which the inhibitor has been injected. 被処理液に含まれる物質を吸着によって除去する吸着システムであって、前記被処理液に接液する接液部の少なくとも一部が金属材料で形成されており、前記被処理液に含まれる物質を吸着する吸着材を有する吸着塔と、前記金属材料のすきま腐食を抑制するための抑制剤を前記被処理液に注入する抑制剤注入装置と、前記被処理液のｐＨを低下させるためのｐＨ調整剤を注入するｐＨ調整剤注入装置と、を備え、前記被処理液は、塩化物イオンを含む液体であり、前記抑制剤は、モリブデン酸イオンを含有する液体であり、
The metal material is duplex stainless steel,
The liquid to be treated into which the inhibitor is injected is
An adsorption system wherein the pH is less than 6.0 and the ratio of the molar concentration of molybdate ions to the molar concentrations of chloride ions is adjusted to 0.1 or more. 被処理液に含まれる物質を吸着によって除去する吸着システムであって、前記被処理液に接液する接液部の少なくとも一部が金属材料で形成されており、前記被処理液に含まれる物質を吸着する吸着材を有する吸着塔と、前記金属材料のすきま腐食を抑制するための抑制剤を前記被処理液に注入する抑制剤注入装置と、前記被処理液のｐＨを低下させるためのｐＨ調整剤を注入するｐＨ調整剤注入装置と、を備え、前記被処理液は、塩化物イオンを含む液体であり、前記抑制剤は、モリブデン酸イオンを含有する液体であり、
The metal material is duplex stainless steel,
The liquid to be treated into which the inhibitor is injected is
An adsorption system having a pH of 6.0 or more and 8.0 or less, and having a molar concentration ratio of molybdate ions to chloride ions adjusted to 0.007 or more. 被処理液に含まれる物質を吸着によって除去する吸着システムであって、前記被処理液に接液する接液部の少なくとも一部が金属材料で形成されており、前記被処理液に含まれる物質を吸着する吸着材を有する吸着塔と、前記金属材料のすきま腐食を抑制するための抑制剤を前記被処理液に注入する抑制剤注入装置と、前記被処理液のｐＨを低下させるためのｐＨ調整剤を注入するｐＨ調整剤注入装置と、を備え、前記被処理液は、塩化物イオンを含む液体であり、前記抑制剤は、モリブデン酸イオンを含有する液体であり、
The metal material is austenitic stainless steel,
The liquid to be treated into which the inhibitor is injected is
An adsorption system wherein the pH is less than 6.0 and the ratio of the molar concentration of molybdate ions to the molar concentrations of chloride ions is adjusted to 0.2 or more. 被処理液に含まれる物質を吸着によって除去する吸着システムであって、前記被処理液に接液する接液部の少なくとも一部が金属材料で形成されており、前記被処理液に含まれる物質を吸着する吸着材を有する吸着塔と、前記金属材料のすきま腐食を抑制するための抑制剤を前記被処理液に注入する抑制剤注入装置と、前記被処理液のｐＨを低下させるためのｐＨ調整剤を注入するｐＨ調整剤注入装置と、を備え、前記被処理液は、塩化物イオンを含む液体であり、前記抑制剤は、モリブデン酸イオンを含有する液体であり、
The metal material is austenitic stainless steel,
The liquid to be treated into which the inhibitor is injected is
An adsorption system having a pH of 6.0 or more and 8.0 or less, and having a molar concentration ratio of molybdate ions to chloride ions adjusted to 0.1 or more. The adsorption system according to any one of claims 9 to 12 ,
The adsorption system is
A supply pipe for supplying the liquid to be treated to the adsorption tower,
The inhibitor injection device injects the inhibitor into the liquid to be treated flowing through the supply pipe,
The pH adjuster injection device is an adsorption system for injecting the pH adjuster into the liquid to be treated into which the inhibitor has been injected.

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