KR101102525B1 - Method for detecting chemical state of high temperature cooling water using electrochemical hydrochemical technology - Google Patents

Abstract

The present invention relates to a method for detecting a chemical state of high temperature cooling water in which dissolved hydrogen is present using an electrochemical hydrochemical technique, and more particularly, a precious metal electrode; A corresponding electrode; And a potential application and current measuring device; It relates to a method for detecting the chemical state of the high temperature cooling water using an electrochemical hydrochemical technique. The method for detecting the chemical state of the high temperature cooling water using the electrochemical hydrochemical technique according to the present invention is to suppress other electrochemical reactions such as oxidation of dissolved hydrogen in the potential region where an oxide film is present in a precious metal such as platinum in a high temperature aqueous solution. By using the phenomenon, it is possible to detect the presence or absence of chlorine ions, pH change and dissolved hydrogen content change in the high temperature aqueous solution by measuring the change of oxidation reaction inhibition region of the precious metal electrode and the oxidation current in the region. This can be useful to find out.

Electrochemistry, Hydrochemistry, Dissolved Hydrogen, High Temperature Cooling Water, Platinum, Precious Metal Electrodes, Chlorine Ion

Description

The method for sensing of chemical environment in high temperature water using electrochemical water chemistry technique}

The present invention relates to a chemical state detection method of high temperature cooling water using electrochemical hydrochemical technology.

One of the main causes of damage and failure of pressure vessels, heat exchanger pipes, water supply pipes, and turbines, which are important for the soundness and economics of high-temperature energy equipment such as nuclear power plants and thermal power plants, is due to corrosion caused by high temperature and high pressure cooling water. Known. At high temperatures, the dissociation constant of the water increases and the chemical ativity of the species that promotes corrosion increases, thereby accelerating the corrosion of the metal. Therefore, structural metal materials in contact with the high temperature system water and the cooling water are exposed to a strong corrosive environment, and therefore, stainless steel or a special alloy resistant to corrosion are generally used. Corrosion studies under high temperature and high pressure environments, which have been actively carried out globally for the past 20 years to advance the life management technology of these energy facilities, can predict corrosion propagation characteristics by major damage types as a function of corrosion potential (CP) and basicity (pH). In order to reduce the corrosion rate of metals at high temperature, monitoring of inflow of impurity ions such as chlorine (Cl) and treatment of chemical additives in high temperature cooling water can reduce the corrosion rate of structural materials. Designed. Typical chemical treatment methods used at high temperatures include increasing the pH of cooling water or injecting hydrogen gas, a reducing agent. Therefore, techniques for measuring pH of high temperature aqueous solution, methods for measuring impurity ions, various methods for measuring dissolved gas, etc. have been developed for corrosion inhibition of structural materials. Niedrach et al. Measured electrochemical potential (ECP) at high temperatures using zirconia electrodes (Angewandte Chemie, Mar 1987. v. 26 (3) p. 161-169). WO 96/22519 has developed a technique for measuring electrochemical potential in a high temperature, high radiation atmosphere using yttria stabilized magnesia (YSM) materials. Electrochemical potential (ECP) is a major measure of the redox state of a medium, but this alone does not provide a detailed description of the various states. In addition, Japanese Patent No. 2000-346791 used an alternating current impedance technique for monitoring material corrosion.

Republic of Korea Patent No. 10-0698506 relates to a corrosion probe for monitoring the corrosion of metal and metal alloys to prevent corrosion of the metal and metal alloy constituting the cooling system in the cooling system using water as a coolant, such as generator stator cooling system. The present invention relates to a sensor for simultaneously measuring corrosion potential and basicity. However, the device is limited to two sensing materials that can cause corrosion of the metal, and there is a problem that the reliability of the sensing ability at high temperature is insufficient. In addition, Korean Patent Laid-Open Publication No. 2003-0033903 relates to Ag / AgCl internal reference electrode for monitoring the corrosive environment of high temperature energy equipment, and can be used stably under high temperature and high pressure hydrochemical technology environment for a long time, and the performance and life of the high temperature energy equipment. A reliable internal reference electrode suitable for monitoring the corrosive environment for improved management. However, the electrode has a problem in that the manufacturing process is complicated and the accurate potential cannot be measured.

Accordingly, the present inventors are studying a method of detecting the chemical state of the high temperature cooling water using electrochemical hydrochemistry, and the manufacturing process is simple and efficiently detects the presence or absence of chlorine ion, pH change and dissolved hydrogen amount in the high temperature aqueous solution. The method was developed and the present invention was completed.

An object of the present invention is to provide a method for detecting the chemical state of high temperature cooling water using electrochemical hydrochemical technology.

In order to achieve the above object, a precious metal electrode; A corresponding electrode; And a potential application and current measuring device; It provides a method for sensing the chemical state of the high temperature cooling water using an electrochemical hydrochemical technology.

The method for detecting the chemical state of the high temperature cooling water using the electrochemical hydrochemical technique according to the present invention is to suppress other electrochemical reactions such as oxidation of dissolved hydrogen in the potential region where an oxide film is present in a precious metal such as platinum in a high temperature aqueous solution. Based on the phenomenon, by using this suppression potential region and a phenomenon in which the current in the region changes sensitively to the chemical state of the aqueous solution, the change of the oxidation reaction suppression region of the precious metal electrode and the oxidation current in the region are measured. By improving the ability to detect the presence or absence of chlorine ions in the aqueous solution, the pH change, the amount of dissolved hydrogen, it can be useful to determine the chemical state of the aqueous solution used at high temperatures.

Precious metal electrodes;

A corresponding electrode; And

Device for applying potential and measuring current;

It provides a method for sensing the chemical state of the high temperature cooling water using an electrochemical hydrochemical technology.

Hereinafter, the present invention will be described in detail.

The method for detecting the chemical state of the high temperature cooling water according to the present invention may be performed by the apparatus of FIGS. 1 and 2, and when an oxidation potential is applied to the precious metal in a high temperature aqueous solution in which dissolved hydrogen is present, a precious metal oxide film is generated to generate the potential region. In addition, other electrochemical reactions, such as oxidation of dissolved hydrogen, are suppressed. The presence of impurity ions, pH change, and dissolved hydrogen amount can be detected based on the potential region where the noble metal oxide film is formed and the oxidation current at the potential. .

In the method for detecting the chemical state of the high temperature cooling water according to the present invention, the precious metal electrode is platinum (Pt), gold (Au), rhenium (Re), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver ( Ag), iridium (Ir), alloys thereof, and the like, and the noble metal electrode preferably includes platinum.

In addition, the counter electrode may use a metal, a conductive nonmetal, or the like, and the pipe itself through which the high temperature cooling water flows may also be used as the counter electrode.

Further, the oxidation potential applied to the noble metal electrode should be limited to the potential region where the oxide film is stably formed on the platinum surface. The potential region varies somewhat depending on the temperature of the aqueous solution, the type and concentration of the electrolyte, the pH, and the surface state of the electrode. However, as shown in FIG. 4, the potential region is generally in a region of + 0.25 V to + 0.25 V (vs. V _ext ). do. Therefore, the applied potential region is preferably a potential region in which the platinum oxide film is stable up to a potential of 1,000 占 ㎷ lower than a potential at which water is oxidized to oxygen gas, and a potential up to a potential of 700 占 ㎷ lower than a potential at which water is oxidized to oxygen gas. It is more preferable that it is an area.

In addition, the method for detecting the chemical state of the high temperature cooling water according to the present invention can be detected through the presence or absence of chlorine ion in the high temperature aqueous solution, the change in pH and the amount of dissolved hydrogen.

The presence or absence of chlorine ions, pH change, and dissolved hydrogen change in the aqueous solution affect the density of the metal oxide film generated in the precious metal electrode, thereby reducing the oxidation current of dissolved hydrogen. Therefore, chlorine ions, pH change, and dissolved hydrogen change which affect the density of the metal oxide film can be detected as the change of the oxidation current (see Experimental Example 4).

Experimental Example 1 Analysis of Electrochemical Behavior with and without Dissolved Hydrogen at Room and High Temperatures

Electrochemical Behavior of Aqueous Boric Acid Solution (0.18 M) with or without Dissolved Hydrogen at Room Temperature Using Platinum Electrode and Electrochemical in Lithium Hydroxide (0.001 M) Boric Acid (0.18 M) Buffer with Dissolved Hydrogen at High Temperature The behavior was analyzed and the results are shown in FIGS. 3 and 4.

As shown in FIG. 3, it can be seen that the oxidation reaction of dissolved hydrogen in a normal temperature atmosphere occurs in a typical electron transfer controlled reaction in which the reaction rate increases as the oxidation potential increases.

On the other hand, as shown in Figure 4, in the case of high-temperature oxidation of dissolved hydrogen it is easy to overcome the activation energy (activation energy) of the reaction when the temperature rises and the mobility (mobility of chemical species) participating in the reaction (mobility species) ) Increases. Therefore, the current increases as the oxidation potential increases at the potential of -0.6 V, but the oxidation of dissolved hydrogen is dominated by the diffusion of dissolved hydrogen from -0.3 V to +0.6 V, which greatly inhibits the oxidation of dissolved hydrogen.

<Experiment 2> Analysis of high temperature redox reaction according to applied potential in the presence of dissolved hydrogen

In the lithium hydroxide boric acid buffer solution containing dissolved hydrogen, the high temperature redox reaction occurring by varying the application potential of the platinum electrode was analyzed, and the results are shown in FIG. 5.

As shown in FIG. 5, the oxidation reaction of dissolved hydrogen in the +0.70 V to +0.75 V potential region is greatly reduced because the platinum oxide film is formed in the potential region. Therefore, the redox state in the high temperature aqueous solution can be analyzed through the rapidly changing current.

Experimental Example 3 Analysis of Electrochemical Behavior According to the Addition of Lithium Hydroxide

The electrochemical behavior of aqueous boric acid solution (0.185 M) with or without lithium hydroxide (0.001 M) was analyzed using a platinum electrode, and the results are shown in FIG. 6.

As shown in FIG. 6, the oxidation current in the region where the oxidation current is minimized is about 4 mA when lithium hydroxide is present (△), but when lithium hydroxide is not present (□), that is, when the pH is lowered. Increased to 15 ㎂. Therefore, since the pH change of the aqueous solution affects the density of the platinum oxide film and reduces the oxidation current of the dissolved hydrogen, it is possible to indirectly detect a factor affecting the density of the platinum oxide film.

Experimental Example 4 Potential Analysis According to the Presence of Chlorine Ion, pH Change, and Dissolved Hydrogen Amount

The presence or absence of chlorine ions, pH change and dissolved hydrogen change were measured by the detection method and the conventional method of the present invention and the results are shown in Table 1 below.

Hydrochemistry Conventional method
(Redox potential) Detection method of the present invention H ₂ diffusion governing oxidation current PtO ₂ stable region current and redox potential Reference potential redox lineman Application temperature condition
High temperature, low temperature High temperature High temperature High temperature, low temperature Steady state standard
(Redox potential) No influence Reference current
(50 ~ 500㎂㎝ ^-2 ) standard
PtO ₂ Stable Potential Chlorine Ion Inflow No change Impact Current increase
(Diffusion governing current) No change pH increase Potential shift
(cathodic) Impact Small current reduction Potential shift
(cathodic) pH reduction Potential shift
(anodic) Impact Current increase Potential shift
(anodic) Dissolved hydrogen increase Potential shift
(cathodic) increase Current increase Potential shift
(cathodic) Dissolved hydrogen reduction Potential shift
(anodic) decrease Small current reduction Potential shift
(anodic)

As shown in Table 1, in the sensing method of the present invention, the oxidation current increases due to the inflow of chlorine ions, but the potential change due to the inflow of chlorine ions does not occur in the conventional method. In addition, the conventional method can not easily grasp the potential change according to the pH change and the amount of dissolved hydrogen, the detection method of the present invention is sensitive to the change in pH, the current is increased or decreased, and also sensitive to the change in the amount of dissolved hydrogen It can be seen that the reaction.

1 is a conceptual diagram illustrating a sensor of the present invention using electrochemical hydrochemical techniques;

2 is another conceptual diagram illustrating a sensor of the present invention using electrochemical hydrochemical techniques;

3 is a graph showing the electrochemical behavior with or without dissolved hydrogen at room temperature;

4 is a graph showing the electrochemical behavior according to the presence of dissolved hydrogen at high temperature;

5 is a graph showing the electrochemical behavior of high temperature redox reactions with applied potential in the presence of dissolved hydrogen; And

6 is a graph showing the electrochemical behavior according to the addition of lithium hydroxide (when lithium hydroxide is present: △ and lithium hydroxide is not present: □)

Claims (10)

Precious metal electrodes; A corresponding electrode; And Device for applying potential and measuring current; Method for detecting the presence or absence of chlorine ions, pH change and dissolved hydrogen amount in the high temperature cooling water using an electrochemical hydrochemical technique comprising a. The method of claim 1, wherein the precious metal electrode is platinum (Pt), gold (Au), rhenium (Re), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag) and iridium (Ir) A method for detecting the presence or absence of chlorine ions, pH change and dissolved hydrogen amount in the high temperature cooling water, characterized in that one or an alloy thereof selected from the group consisting of. 3. The method of claim 2, wherein the precious metal electrode comprises platinum (Pt). 4. The method of claim 1, wherein the counter electrode is a metal or a conductive nonmetal. The method of claim 1, wherein the corresponding electrode is a pipe itself through which the high temperature cooling water flows. According to claim 1, wherein the oxidation potential applied to the noble metal electrode is chlorine ion presence in the high-temperature cooling water, characterized in that ± 700 mV potential region, respectively, based on the potential of the water is oxidized to oxygen gas, How to detect changes in pH and changes in dissolved hydrogen. delete The method according to claim 1, wherein the presence or absence of chlorine ions in the high temperature cooling water, the presence or absence of chlorine ions in the high temperature cooling water, by measuring the degree of chlorine ion on the density of the noble metal oxide on the sensor surface by the change of the oxidation current, pH How to detect changes and changes in dissolved hydrogen content. The method of claim 1, wherein the change in pH is measured by detecting the change in the density of the noble metal oxide on the sensor surface and the redox reaction by the change in oxidation current, the presence or absence of chlorine ion in the high temperature cooling water, pH change And detecting a change in dissolved hydrogen content. The method according to claim 1, wherein the amount of dissolved hydrogen is measured by detecting the effect of dissolved hydrogen from the change in the density of the noble metal oxide on the sensor surface as a change in oxidation current, and the pH change in the high temperature cooling water. And detecting a change in dissolved hydrogen content.

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