Scale layer preparation method and steam generator secondary side test sample

Abstract

The invention discloses a method for preparing a scale layer on a secondary side of a steam generator and a test sample piece on the secondary side of the steam generator. The method comprises the following steps: dissolving ferric salt, oxysalt, an acid compound and an organic solvent in deionized water to form a mixed aqueous solution; taking the mixed aqueous solution as a raw material, and depositing a scale layer precursor on a test sample on the secondary side of a steam generator by adopting a hydrothermal method; and heating the scale layer precursor in an inert gas atmosphere so as to form a simulated scale layer on the test sample. According to the method, preparation of the simulated scale layer is completed based on hydrothermal synthesis-high-temperature firing, the ultra-long period of preparing the simulated scale layer through high-temperature and high-pressure corrosion is avoided, rapid preparation of the steam generator secondary side sample sediment simulated scale layer is achieved, and the deposited scale layer growing closer to the actual operation environment can be simulated.

Description

Technical Field

[0001] The present application relates to the field of power technologies, and particularly to a method for preparing a scale layer on the secondary side of a steam generator and a test specimen for the secondary side of a steam generator. Background Art

[0002] Currently, during the operation of a pressurized water reactor, in the phase change process where the secondary side medium gradually changes from a subcooled state to a superheated state, due to the use of a large amount of carbon steel materials in the secondary loop equipment, during the phase change process, its corrosion products will form a mixture of Fe2O3 and Fe3O4 in the medium. These iron oxides will flow with the medium and continuously deposit on the heat transfer tubes, tube sheets, support plates, etc. on the secondary side of the steam generator (Steam Generator, SG) to form dirt, affecting the heat transfer efficiency, operation safety, and stability of the steam generator. In addition, the deposits will cause corrosion of the materials on the secondary side of the steam generator, resulting in stress corrosion of the heat transfer tubes and possibly further leading to unplanned reactor shutdowns, causing huge economic losses.

[0003] To solve the problem of huge economic losses caused by deposits on the secondary side of the steam generator, it is usually necessary to clean the steam generator, and chemical cleaning is a method with good effect and low cost among them. In related technologies, taking the heat transfer tubes on the secondary side of the actually operating steam generator as test specimens, scale layers are deposited on the heat transfer tubes on the secondary side of the steam generator by adding raw materials. However, it takes more than 1 year for the scale to grow, and the detection cost is relatively high.

[0004] Therefore, in order to smoothly carry out the chemical cleaning simulation test of the steam generator, how to quickly generate scale layers with the required thickness, density, and heat transfer coefficient on the secondary side of the steam generator to provide a technical basis for subsequent research on scale removal is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present application provides a method for preparing a scale layer on the secondary side of a steam generator and a test specimen for the secondary side of a steam generator. By using hydrothermal synthesis to deposit on the surface of the simulation specimen and then calcining, the preparation of a simulated scale layer of the deposits on the secondary side specimen of the steam generator is realized.

[0006] According to one aspect of the present application, a method for preparing a scale layer on the secondary side of a steam generator is provided, including:

[0007] Dissolve iron salts, oxygen-containing salts, acid compounds, and organic solvents in deionized water to form a mixed aqueous solution;

[0008] Using the mixed aqueous solution as a raw material, deposit a scale layer precursor on the test specimen on the secondary side of the steam generator by hydrothermal method;

[0009] Under an inert gas atmosphere, the scale precursor is heat-treated to form a simulated scale on the test specimen.

[0010] Optionally, the concentration of iron ions in the mixed aqueous solution is 2300 ppm to 5000 ppm.

[0011] Optionally, the hydrothermal reaction temperature is 80°C to 120°C, and the hydrothermal reaction time is 3 h to 4 h.

[0012] Optionally, the heating temperature of the heat treatment is 350°C to 450°C, and the heating time is 1.5 h to 2.5 h.

[0013] Optionally, the iron salt is ferric chloride, ferrous sulfate, ferric nitrate or ferric sulfate;

[0014] The oxygen-containing salt is nitrate or sulfate;

[0015] The acid compound is hydrochloric acid, nitric acid, sulfuric acid, acetic acid or oxalic acid;

[0016] The organic solvent is methyl cyanide.

[0017] Optionally, the molar ratio of the iron salt, the oxygen-containing salt, and the acid compound is 4 to 10: 35 to 130: 0.8 to 2.5.

[0018] Optionally, before depositing the scale precursor on the test specimen on the secondary side of the steam generator by the hydrothermal method, the scale preparation method on the secondary side of the steam generator further includes:

[0019] Grind the test specimen and clean the test specimen with deionized water and ethanol.

[0020] Optionally, before heat-treating the scale precursor under an inert gas atmosphere, the scale preparation method on the secondary side of the steam generator further includes:

[0021] After hydrothermal cooling, clean and dry the test specimen deposited with the scale precursor with deionized water and ethanol.

[0022] Optionally, the scale preparation method on the secondary side of the steam generator further includes:

[0023] Weigh the first mass of the test specimen without depositing the scale precursor and the second mass of the test specimen deposited with the simulated scale respectively;

[0024] Calculate the difference between the second mass and the first mass to determine the scale mass;

[0025] If the mass of the scale layer is less than the preset mass, using the mixed aqueous solution as a raw material, the scale layer precursor is repeatedly deposited on the test sample by a hydrothermal method, and the scale layer precursor is heat-treated until the mass of the scale layer is greater than or equal to the preset mass.

[0026] Optionally, using the mixed aqueous solution as a raw material, depositing a scale layer precursor on a test sample on the secondary side of a steam generator by a hydrothermal method includes:

[0027] Adding the mixed aqueous solution to a reaction kettle containing the test sample;

[0028] Heating the sealed reaction kettle according to the hydrothermal reaction temperature and hydrothermal reaction time;

[0029] After cooling, taking out the test sample deposited with the scale layer precursor from the reaction kettle.

[0030] According to another aspect of the present application, a test sample on the secondary side of a steam generator is provided, and the surface of the test sample is coated with a simulated scale layer prepared by the scale layer preparation method on the secondary side of the steam generator.

[0031] By means of the above technical solution, a scale layer precursor is synthesized on the surface of a simulation sample on the secondary side of a steam generator by a hydrothermal method, and then the scale layer precursor is heat-treated by burning, so that a required simulated scale layer is formed on the test sample. On the one hand, using an organic solvent as a medium to dissolve iron salts not only fully disperses the iron salts in the reaction system, increases the iron ion concentration of the mixed aqueous solution as a raw material, so that a simulated scale layer similar to the actual deposit can be obtained within a few hours by the hydrothermal method, greatly shortening the scale formation preparation time and reducing the test cost, but also the organic solvent can change the viscosity and diffusion coefficient of the reaction system, which helps to generate a more uniform and dense iron scale structure. On the other hand, the hydrothermal method can carry out reactions under relatively mild conditions. By controlling parameters such as reaction temperature, pressure, time and solution composition, the composition, structure and morphology of the scale layer precursor can be accurately and conveniently controlled to meet the requirements of different test areas for the thickness, density and heat transfer coefficient of the dirt, which is beneficial to evaluating the differences in dirt cleaning on the secondary side of the steam generator. On the other hand, through burning, impurities such as water and organic matter can be effectively removed, improving the purity and quality of the scale layer. At the same time, it can cause the scale layer precursor to crystallize and undergo a phase change, forming a more stable scale layer structure to simulate a deposited scale layer that grows closer to the actual operating environment.

[0032] The above description is only an overview of the technical solution of the present application. In order to be able to understand the technical means of the present application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present application more obvious and understandable, the following specifically gives the specific implementation manners of the present application. Brief Description of the Drawings

[0033] The drawings described herein are provided to further understand the present application and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not unduly limit the present application. In the drawings:

[0034] Figure 1 It shows a schematic flow chart of the method for preparing the scale layer on the secondary side of the steam generator provided by the embodiment of the present application;

[0035] Figure 2 It shows a schematic diagram of the microscopic structure of the simulated scale layer provided by the embodiment of the present application;

[0036] Figure 3 It shows an energy spectrum diagram of the simulated scale layer provided by the embodiment of the present application. Detailed Description of the Embodiments

[0037] The present application will be described in detail below with reference to the drawings and in conjunction with the embodiments. It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0038] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present application and should not be construed as limiting the present application.

[0039] Those skilled in the art of the present technology can understand that, unless specifically stated otherwise, the singular forms "a", "an", "the" and "said" used herein may also include the plural forms. It should be further understood that the term "comprising" used in the specification of the present application means the presence of the described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups. It should be understood that when we say that an element is "connected" or "joined" to another element, it can be directly connected or joined to other elements, or there may also be intermediate elements. In addition, the "connection" or "joining" used herein may include wireless connection or wireless coupling. The phrase "and / or" used herein includes all or any unit and all combinations of one or more related listed items.

[0040] Now, exemplary embodiments according to the present application will be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many different forms and should not be construed as being limited only to the embodiments set forth herein. It should be understood that these embodiments are provided so that the disclosure of the present application is thorough and complete, and the concept of these exemplary embodiments is fully conveyed to those of ordinary skill in the art.

[0041] In this embodiment, a method for preparing a scale layer on the secondary side of a steam generator is provided. As Figure 1 shown, the method includes:

[0042] Step 101, dissolve iron salts, oxygen-containing salts, acid compounds, and organic solvents in deionized water to form a mixed aqueous solution.

[0043] Specifically, the iron salts are ferric chloride (FeCl3), ferric sulfate (Fe2(SO4)3), ferrous sulfate (FeSO4), or ferric nitrate (Fe(NO3)3). The oxygen-containing salts are nitrates or sulfates, such as sodium nitrate (NaNO3). The acid compounds are hydrochloric acid (HCl), nitric acid (HNO3), sulfuric acid (H2SO4), acetic acid (C2H4O2), or oxalic acid (H2C2O4). The organic solvent is methyl cyanide (CH3CN).

[0044] Furthermore, the concentration of iron ions in the mixed aqueous solution is 2300 ppm to 5000 ppm. For example, the mixed aqueous solution is configured according to an iron ion concentration of 2800 ppm or according to an iron ion concentration of 4100 ppm. The higher the iron ion concentration, the faster the iron scale formation rate, and it is beneficial to prepare a denser and harder iron scale structure. It can not only reproduce the scale layer characteristics of different heat exchange regions on the secondary side of the steam generator, but also significantly improve the simulation scale preparation efficiency and shorten the required preparation time.

[0045] In this embodiment, the mixed iron salts, oxygen-containing salts, acid compounds, organic solvents, and deionized water are dissolved to form a mixed aqueous solution. Using the organic solvent as a medium to dissolve the iron salts and oxygen-containing salts not only fully disperses the iron salts and oxygen-containing salts in the reaction system, increases the iron ion concentration of the mixed aqueous solution as a raw material, but also can change the viscosity and diffusion coefficient of the reaction system. Thus, a simulated scale layer similar to the actual deposit can be obtained within a few hours by the hydrothermal method, greatly shortening the scale formation preparation time, reducing the test cost, and contributing to the formation of a more uniform and dense iron scale structure.

[0046] In one embodiment, the molar ratio of the iron salt, the oxygen-containing salt, and the acid compound is 4 to 10: 35 to 130: 0.8 to 2.5. In this way, the ratio of the iron salt to the acid compound is appropriate, which can not only ensure the proper release and activity of iron ions, inhibit the formation of iron hydroxide precipitation, but also prevent the reaction from being too fast to control due to excessive acidity. The higher proportion of the oxygen-containing salt can provide a stable anion environment, interact with iron ions, and jointly promote the oxidation reaction rate, which is beneficial to the formation of the simulated scale layer.

[0047] Step 102: Using the mixed aqueous solution as the raw material, a scale layer precursor is deposited on the test specimen on the secondary side of the steam generator by the hydrothermal method.

[0048] Among them, the test specimen can be a structural member made of the same material as the steam generator. The simulated specimen can be an irregular surface or a smooth surface, and the shape of the test specimen can be reasonably set according to the test requirements.

[0049] In this embodiment, under the influence of the acid compound, the iron salt in the high-temperature and high-pressure mixed aqueous solution undergoes a hydrolysis reaction to decompose into iron ions, and the iron ions are oxidized by the acid radical ions of the oxygen-containing salt to form iron scale precipitation. Thus, the scale layer precursor can be rapidly prepared, and the hydrothermal preparation process is relatively simple, and the process parameters are easy to control, further reducing the cost and difficulty of preparing the simulated scale layer. In addition, the hydrothermal method can carry out the reaction under relatively mild conditions. By controlling parameters such as the reaction temperature, pressure, time, and solution composition, the composition, structure, and morphology of the scale layer precursor can be accurately and conveniently controlled to meet the requirements for the thickness, density, and heat transfer coefficient of the fouling in different test areas, which is beneficial to evaluating the differences in the cleaning of the fouling on the secondary side of the steam generator.

[0050] Specifically, the hydrothermal reaction temperature is 80°C to 120°C. Since the concentration of iron ions in the raw material is relatively high, when it can provide sufficient energy for the reaction, as low a reaction temperature as possible can reduce the requirements for the reaction equipment, thereby taking into account both the reaction rate and the equipment operation cost. The hydrothermal reaction time is 3h to 4h, and the hydrothermal reaction time can be reasonably set according to the required scale layer quality or thickness, and the embodiments of the present application will not be listed one by one.

[0051] In the actual application scenario, step 102, that is, using the mixed aqueous solution as the raw material and depositing the scale layer precursor on the test specimen on the secondary side of the steam generator by the hydrothermal method, specifically includes: adding the mixed aqueous solution to the reaction kettle containing the test specimen; heating the sealed reaction kettle according to the hydrothermal reaction temperature and the hydrothermal reaction time; after cooling, taking out the test specimen deposited with the scale layer precursor from the reaction kettle.

[0052] In one embodiment, before depositing the scale precursor on the test specimen on the secondary side of the steam generator by the hydrothermal method, the test specimen can be polished first to make the surface of the test specimen free of foreign objects and relatively rough microscopically, which can enhance the connection strength between the scale layer and the test specimen, so as to facilitate the better adhesion of the scale layer on the surface of the test specimen. Then, the polished test specimen is cleaned with deionized water and ethanol. On the one hand, the surface tension of the test specimen surface is reduced by ethanol, and at the same time, some organic substances are dissolved. On the other hand, the dirt on the surface of the test specimen is washed away by deionized water to ensure the purity of the specimen surface, so that the scale layer can grow better on the test specimen.

[0053] Step 103, under an inert gas atmosphere, the scale precursor is heat-treated to form a simulated scale layer on the test specimen.

[0054] Specifically, the heating temperature of the heat treatment is 350°C to 450°C, and the heating time is 1.5 h to 2.5 h. The mass of the simulated scale layer is 0.03 - 0.25 g.

[0055] In this embodiment, after obtaining the scale precursor, through heat treatment, impurities such as moisture and organic substances can be effectively removed, the purity and quality of the scale layer can be improved. At the same time, the scale precursor can crystallize and undergo a phase change to form a more stable scale layer structure, so as to simulate a deposited scale layer that grows closer to the actual operating environment.

[0056] In one embodiment, before heat-treating the scale precursor, after hydrothermal cooling, the test specimen deposited with the scale precursor can also be cleaned again with deionized water and ethanol to remove iron scale particles and some organic substances with low adhesion strength, and finally, the excess water and ethanol are volatilized through drying treatment. This helps to improve the quality of the prepared simulated scale layer and provides a reliable experimental basic material for subsequent scale layer cleaning experiments.

[0057] In one embodiment, the scale layer preparation method on the secondary side of the steam generator further includes: respectively weighing the first mass of the test specimen without depositing the scale precursor and the second mass of the test specimen deposited with the simulated scale layer; calculating the difference between the second mass and the first mass to determine the scale layer mass; if the scale layer mass is less than the preset mass, then using the mixed aqueous solution as the raw material, repeating the deposition of the scale precursor on the test specimen by the hydrothermal method and heat-treating the scale precursor until the scale layer mass is greater than or equal to the preset mass.

[0058] In this embodiment, if the mass of the simulated scale obtained by one hydrothermal reaction cannot meet the preset mass required for the experiment, then the hydrothermal method and calcination are repeated to prepare a new scale layer on the test specimen with the existing simulated scale to meet different experimental requirements. Specific Example 1:

[0060] Step 1: Polish the surface of the secondary-side sample with fine sandpaper until the surface is smooth and free of foreign objects, and ultrasonically clean it with deionized water and ethanol for 5 to 10 minutes each at room temperature, then air dry it naturally or dry it under vacuum at room temperature for standby.

[0061] Step 2: Accurately weigh the mass of the secondary-side sample with an analytical balance and record it as m0. This is the mass of the sample without the simulated fouling layer of secondary-side deposits (the first mass).

[0062] Step 3: Take a 100 mL beaker, add 0.65 g of ferric chloride, 3.4 g of sodium nitrate, 40 mL of 0.1% hydrochloric acid, 28 mL of acetonitrile, and 12 mL of deionized water. After mixing, stir magnetically to dissolve and obtain a mixed aqueous solution.

[0063] Step 4: Transfer the secondary-side sample that has completed mass measurement to a clean autoclave. Taking a sample with a surface area of 20 cm 2 as an example, add 80 mL of the mixed aqueous solution, and carry out a hydrothermal reaction at 100 °C for 4 h to obtain a simulated fouling layer precursor.

[0064] Step 5: After cooling to room temperature, take out the test sample from the autoclave, and clean the surface precursor of the sample with deionized water and ethanol, then air dry it naturally or dry it under vacuum at room temperature.

[0065] Step 6: Transfer the treated test sample to a tubular furnace, introduce an inert gas (nitrogen or argon) at 40 mL / min, control the temperature to rise to 400 °C and calcine for 2 h. After cooling to room temperature, take out the sample to obtain a simulated fouling layer of the secondary side of the steam generator.

[0066] Step 7: Weigh the sample with the simulated fouling layer attached using an analytical balance, and record the mass as m1. This is the sum of the mass of the secondary-side sample and the simulated fouling layer coated on its outside (the second mass). Calculate the difference between m1 and m0, which is the mass m of the simulated fouling layer.

[0067] Based on the above example, the mass of the simulated fouling layer of the secondary side of the steam generator prepared by the hydrothermal synthesis - high-temperature calcination method is 0.03 g. The micrograph of this simulated fouling layer is as Figure 2 shown. It can be seen from Figure 2 that a dense fouling layer is formed on the surface of the sample. The energy spectrum diagram of this simulated fouling layer is as Figure 3 shown. It can be seen from Figure 3 that the energies of iron and oxygen elements in the simulated fouling layer are relatively high, indicating that the components of the simulated fouling layer are mostly Fe2O3 and Fe3O4, meeting the requirements of the chemical cleaning simulation test of the steam generator. Specific Example 2:

[0069] Step 1: Polish the surface of the secondary side sample with fine sandpaper until the surface is smooth and free of foreign matters, and ultrasonically clean it with deionized water and ethanol for 5 to 10 minutes each at room temperature, then air dry it naturally or dry it under vacuum at room temperature for standby.

[0070] Step 2: Accurately weigh the mass of the secondary side sample with an analytical balance, and record it as m0. This is the mass of the sample without the simulated fouling layer of secondary side deposits (the first mass).

[0071] Step 3: Take a 150 mL beaker, add 1.94 g of ferric sulfate, 8.92 g of sodium sulfate, 1 mL of 15% oxalic acid, 74 mL of acetonitrile, and 50 mL of deionized water. After mixing, stir and dissolve it magnetically to obtain a mixed aqueous solution.

[0072] Step 4: Transfer the secondary side sample whose mass has been measured to a clean autoclave. Taking a sample with a surface area of 20 cm 2 as an example, add 80 mL of the mixed aqueous solution, and carry out a hydrothermal reaction at 120 °C for 4 h to obtain a simulated fouling layer precursor.

[0073] Step 5: After cooling to room temperature, take out the test sample from the autoclave, and wash the surface precursor of the sample with deionized water and ethanol, then air dry it naturally or dry it under vacuum at room temperature.

[0074] Step 6: Transfer the processed test sample to a tubular furnace, introduce an inert gas (nitrogen or argon) at 40 mL / min, control the temperature to rise to 450 °C and burn for 2.5 h. After cooling to room temperature, take out the sample to obtain a simulated fouling layer of the secondary side deposits of the steam generator.

[0075] Step 7: Weigh the sample with the simulated fouling layer attached with an analytical balance, and record the mass as m1. This is the sum of the mass of the secondary side sample and the simulated fouling layer coated on its outside (the second mass). Calculate the difference between m1 and m0, which is the mass m of the simulated fouling layer.

[0076] The mass of the simulated fouling layer obtained by the preparation method of the simulated fouling layer of the secondary side deposits of the steam generator by hydrothermal synthesis - high-temperature calcination based on the above embodiments is 0.1 g. Specific Example 3:

[0078] Step 1: Polish the surface of the secondary side sample with fine sandpaper until the surface is smooth and free of foreign matters, and ultrasonically clean it with deionized water and ethanol for 5 to 10 minutes each at room temperature, then air dry it naturally or dry it under vacuum at room temperature for standby.

[0079] Step 2: Accurately weigh the mass of the secondary side sample with an analytical balance, and record it as m0. This is the mass of the sample without the simulated fouling layer of secondary side deposits (the first mass).

[0080] Step 3: Take a 150 mL beaker, add 2.1 g of iron nitrate, 6.4 g of sodium nitrate, 1 mL of 15% oxalic acid, 54 mL of acetonitrile, and 30 mL of deionized water. After mixing, stir magnetically to dissolve and obtain a mixed aqueous solution.

[0081] Step 4: Transfer the secondary side sample whose mass has been measured to a clean autoclave. Taking a sample with a surface area of 20 cm 2 as an example, add 80 mL of the mixed aqueous solution, and carry out a hydrothermal reaction at 120 °C for 4 h to obtain a simulated scale precursor.

[0082] Step 5: After cooling to room temperature, take out the test sample from the autoclave, wash the surface precursor of the sample with deionized water and ethanol, and dry it naturally or by vacuum drying at room temperature.

[0083] Step 6: Transfer the processed test sample to a tube furnace, introduce an inert gas (nitrogen or argon) at 40 mL / min, control the temperature to rise to 350 °C and calcine for 2.5 h. After cooling to room temperature, take out the sample to obtain a simulated scale of the secondary side deposit of the steam generator.

[0084] Step 7: Weigh the sample with the simulated scale attached using an analytical balance, and record the mass as m1, which is the sum of the mass of the secondary side sample and the simulated scale coated on its outside (the second mass). Calculate the difference between m1 and m0, which is the mass m of the simulated scale.

[0085] The mass of the simulated scale obtained by the preparation method of the simulated scale of the secondary side deposit of the steam generator by hydrothermal synthesis - high - temperature calcination based on the above - mentioned embodiment is 0.15 g.

[0086] Those skilled in the art can understand that the drawings are only schematic diagrams of a preferred implementation scenario, and the modules or processes in the drawings are not necessarily essential for implementing the present application. Those skilled in the art can understand that the modules in the device in the implementation scenario can be distributed in the device in the implementation scenario according to the description of the implementation scenario, or can be changed accordingly and located in one or more devices different from the present implementation scenario. The modules in the above - mentioned implementation scenario can be combined into one module, or further split into multiple sub - modules.

[0087] The above serial numbers of the present application are only for description and do not represent the advantages or disadvantages of the implementation scenarios. The above - disclosed are only several specific implementation scenarios of the present application. However, the present application is not limited thereto, and any changes that can be thought of by those skilled in the art should fall within the protection scope of the present application.

Claims

1. A method for preparing a scale layer on the secondary side of a steam generator, characterized in that: The method comprises: Dissolving iron salt, oxygen-containing acid salt, acid compound and organic solvent in deionized water to form a mixed aqueous solution; Using the mixed aqueous solution as a raw material, a scale precursor is deposited on a test sample on the secondary side of a steam generator by a hydrothermal method; The scale layer precursor is heated under an inert gas atmosphere to form a simulated scale layer on the test sample.

2. The method for preparing the scale layer on the secondary side of a steam generator according to claim 1, characterized in that: The concentration of iron ions in the mixed aqueous solution is 2300ppm to 5000ppm.

3. The method for preparing the scale layer on the secondary side of a steam generator according to claim 1, characterized in that: The hydrothermal reaction temperature is 80°C to 120°C, and the hydrothermal reaction time is 3h to 4h.

4. The method for preparing a scale layer on the secondary side of a steam generator according to claim 1, characterized in that: The heating temperature of the heat treatment is 350°C to 450°C, and the heating time is 1.5h to 2.5h.

5. The method for preparing the scale layer on the secondary side of a steam generator according to claim 1, characterized in that: The iron salt is ferric chloride, ferrous sulfate, ferric nitrate or ferric sulfate; The oxygen-containing acid salt is nitrate or sulfate; The acid compound is hydrochloric acid, nitric acid, sulfuric acid, acetic acid or oxalic acid; The organic solvent is methyl cyanide.

6. The method for preparing a scale layer on the secondary side of a steam generator according to claim 1, characterized in that: The molar ratio of the iron salt, the oxygen-containing acid salt and the acid compound is 4-10:35-130:0.8-2.

5.

7. The method for preparing a scale layer on the secondary side of a steam generator according to claim 1, characterized in that: Before depositing the scale precursor on the test sample on the secondary side of the steam generator by the hydrothermal method, the method further comprises: polishing the test sample, and cleaning the test sample with deionized water and ethanol; Before the scale layer precursor is subjected to a heating treatment in an inert gas atmosphere, the method further comprises: after hydrothermal cooling, washing the test sample on which the scale layer precursor is deposited with deionized water and ethanol and drying.

8. The method for preparing a scale layer on the secondary side of a steam generator according to claim 1, characterized in that: The method further comprises: Weighing respectively a first mass of the test sample without the deposited scale layer precursor and a second mass of the test sample with the deposited simulated scale layer; Calculating the difference between the second mass and the first mass to determine the mass of the scale layer; If the mass of the scale layer is less than the preset mass, the mixed aqueous solution is used as a raw material to repeatedly deposit a scale layer precursor on the test sample by a hydrothermal method, and the scale layer precursor is heated until the mass of the scale layer is greater than or equal to the preset mass.

9. The method for preparing a scale layer on the secondary side of a steam generator according to claim 1, characterized in that: The method uses the mixed aqueous solution as a raw material and adopts a hydrothermal method to deposit a scale layer precursor on a test sample on the secondary side of a steam generator, comprising: Adding the mixed aqueous solution into the reaction kettle in which the test sample is placed; heating the sealed reactor according to the hydrothermal reaction temperature and hydrothermal reaction time; After cooling, the test sample on which the scale layer precursor is deposited is taken out from the reactor.

10. A test sample for the secondary side of a steam generator, characterized in that: The surface of the test sample is coated with a simulated scale layer prepared by the scale layer preparation method for the secondary side of a steam generator according to any one of claims 1 to 9.

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