An Evaluation Method for the Dynamic Cleaning Effect of EDTA on Corroded Hollow Copper Conductors of Generators

Abstract

The present invention discloses a method for evaluating the EDTA dynamic cleaning effect of corroded hollow copper wires of a generator. In the present invention, an aqueous solution of pure disodium EDTA is used as a flexible chemical cleaning agent to dynamically clean the actual corroded hollow copper wires. The water samples of the cleaning solution are collected at regular intervals and cooled to room temperature. The absorbance of the water samples under light of 265.6 nm is measured. The content of copper oxide dissolved by cleaning (calculated by copper content) is calculated according to the working curve of absorbance and the concentration of Cu-EDTA complex. The experimental data of copper content and cleaning time are linearly fitted, and the slope obtained by fitting is the cleaning apparent rate constant under specific conditions. The magnitude of this parameter can be used to quantitatively characterize the speed of the cleaning rate, thereby guiding the optimization of cleaning conditions. The present invention overcomes the deficiencies of the static dissolution qualitative evaluation method of corrosion products used in previous laboratory cleaning small-scale tests, and provides a scientific method basis for optimizing cleaning conditions in the laboratory.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical cleaning engineering for power generation equipment, and particularly relates to a method for evaluating the EDTA dynamic cleaning effect of corroded hollow copper conductors of a generator. Background Art

[0002] During the operation of generators in nuclear power, thermal power, and hydropower plants, a large amount of waste heat is generated in the stator copper coils. To remove this part of the waste heat, cooling water is often passed through the hollow copper conductors of the generator stator. Since the cooling water has a certain corrosive effect on the copper conductors, the copper conductors will corrode during the long-term operation, shutdown, and maintenance of the system. The corrosion products generated by corrosion will deposit in the system, which will cause system abnormalities such as local overheating. In severe cases, it may even lead to safety accidents such as insulation layer breakdown and unit unplanned shutdown. Therefore, when the system operation state reaches the chemical cleaning condition, it is necessary to chemically clean the corroded hollow copper conductors.

[0003] Currently, the most commonly used chemical cleaning method uses various organic acids and inorganic acids as the effective components of the cleaning. At the same time, to control the corrosion rate of the copper substrate not to exceed the relevant requirements, it is also necessary to additionally add a relatively high concentration of BTA or MBT copper-specific corrosion inhibitor. This cleaning method of strong chemical pickling compounded with a copper corrosion inhibitor can effectively dissolve the copper corrosion products deposited in the system, but the treatment of the waste liquid generated by the cleaning is extremely difficult, especially when the current environmental protection requirements for industrial external drainage are becoming increasingly strict. The high-concentration and difficult-to-degrade organic substances in the cleaning waste liquid have high treatment costs and long treatment cycles. The treatment of the cleaning waste liquid undoubtedly greatly increases the cleaning cost of the corroded hollow copper conductors.

[0004] Before chemically cleaning the on-site system, it is necessary to first carry out a small-scale cleaning test in the laboratory to optimize the cleaning conditions. In previous studies, generally, the corrosion products flushed out from the system were used as the objects of the cleaning test, and the static dissolution method was used to observe whether the corrosion products would be dissolved, so as to evaluate the cleaning effect. However, this test method has the following two deficiencies: on the one hand, it does not simulate the real cleaning conditions. When chemically cleaning the on-site system, the cleaning liquid acts on the corrosion products attached to the inner surface of the hollow copper conductor in a circulating flow manner. Under this circulating flow condition, the mass transfer of the effective components in the cleaning liquid to the corrosion layer and the mass transfer of the dissolved corrosion products to the cleaning liquid are relatively fast. However, the current static dissolution test of the corrosion products cannot simulate the flowing scouring effect of the cleaning liquid on the real corrosion layer; on the other hand, it cannot quantitatively characterize the speed of the cleaning rate. The observation method can only qualitatively obtain whether the corrosion products are dissolved, but cannot quantitatively characterize the dissolution rate of the corrosion layer during the cleaning process.

[0005] Considering the above two deficiencies, the results obtained by the current laboratory small-scale cleaning test method have little guidance for the actual cleaning of the system. Summary of the Invention

[0006] Aiming at the problems existing in the existing laboratory cleaning small-scale test method for corroded hollow copper wires of generators, a method for evaluating the EDTA dynamic cleaning effect of corroded hollow copper wires of generators is provided. Under the condition of simulating actual dynamic cleaning, the corroded hollow copper wires are cleaned with EDTA, providing a method basis for optimizing the cleaning test conditions, so as to better guide the cleaning of on-site systems.

[0007] The specific technical solution is as follows:

[0008] A method for evaluating the EDTA dynamic cleaning effect of corroded hollow copper wires of generators, characterized by including the following steps:

[0009] 1) Prepare corroded hollow copper wire specimens;

[0010] 2) Configure a series of concentrations of Cu-EDTA complex solutions, measure the absorbance of the solutions at 265.6 nm, and plot the Cu-EDTA complex concentration-absorbance working curve;

[0011] 3) Use the disodium EDTA aqueous solution preheated to a certain temperature as the cleaning agent to dynamically clean the corroded hollow copper wire specimens. Collect the cleaning liquid water samples at regular intervals and cool them to room temperature. Measure the absorbance of the water samples under the light of 265.6 nm. Calculate the copper content dissolved by cleaning according to the working curve, perform linear fitting on the copper content and the cleaning time. The slope obtained by fitting is the cleaning apparent rate constant, and the speed of the cleaning rate is quantitatively characterized according to the magnitude of the cleaning apparent rate constant.

[0012] The above method for evaluating the EDTA dynamic cleaning effect of corroded hollow copper wires of generators is further characterized in that the method for preparing the corroded hollow copper wire specimens in step 1) is: strip the surface insulation layer of the actual corroded hollow copper wire taken from the site, cut it into small sections, encapsulate the copper wire specimens with heat-shrinkable round tubes, and then tie the two ends of the specimens firmly.

[0013] The above method for evaluating the EDTA dynamic cleaning effect of corroded hollow copper wires of generators is further characterized in that the dynamic cleaning method in step 3) is: make the cleaning liquid flow through the corroded hollow copper wire specimens at a certain flow rate to clean the specimens under simulated real cleaning conditions.

[0014] The disodium EDTA solution is slightly acidic and has a strong complexing effect on copper ions (the logarithm of the stability complex constant lgK is as high as 18.8), which can dissolve copper oxides. At the same time, the disodium EDTA solution has a slight corrosive effect on the copper substrate, and can flexibly chemically clean the hollow copper wire without adding a copper corrosion inhibitor. The cleaning agent with a single component also provides a prerequisite for the rapid characterization of the cleaning effect.

[0015] The Cu-EDTA complex formed by copper oxide and EDTA is blue, and the copper content in the cleaning solution can be quickly determined by spectrophotometry. Moreover, the EDTA cleaning reaction of the corroded hollow copper wire is clear, the composition of its corrosion products is simple, and the components of the effective components in the cleaning solution and the products generated by cleaning are single. Therefore, the content of dissolved copper oxide can be quickly characterized according to the absorbance of the Cu-EDTA complex at the characteristic wavelength of 265.6 nm.

[0016] The beneficial effects of the above solution are:

[0017] The method provided by this application can evaluate the flexible dynamic cleaning effect of the actually corroded hollow copper wire. The measured cleaning apparent rate constant can be used to quantitatively characterize the rate of EDTA cleaning of copper corrosion products, overcoming the deficiencies of the static dissolution qualitative evaluation method of corrosion products used in previous laboratory cleaning small-scale tests, providing a scientific method basis for optimizing cleaning conditions in the laboratory, and being able to better guide the chemical cleaning of actual systems. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the dynamic cleaning device provided in the embodiment of the present invention;

[0019] Figure 2 is Figure 1 A schematic diagram of the structure of the corroded hollow copper wire specimen;

[0020] Figure 3 It is a diagram showing the influence of the cleaning solution temperature on the EDTA cleaning effect of the corroded hollow copper wire;

[0021] Figure 4 It is a diagram showing the influence of the cleaning solution concentration on the EDTA cleaning effect of the corroded hollow copper wire.

[0022] In the drawings: 1. Thermostatic heating magnetic stirrer; 2. Cleaning solution water tank; 3. Stirring magnetic bar; 4. Peristaltic pump; 5. Corroded hollow copper wire specimen; 51. Adapter; 52. Heat shrinkable round tube; 53. Plastic tie; 54. Corroded hollow copper wire; 6. Quartz cuvette; 7. Ultraviolet absorbance measurement and data analysis system. Detailed Embodiments

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0025] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but it is not limited to the present invention.

[0026] Embodiment 1

[0027] In this embodiment, a method for evaluating the EDTA dynamic cleaning effect of corroded hollow copper wires of a generator is provided, and the steps are as follows:

[0028] 1) Prepare corroded hollow copper wire specimens

[0029] Take out the corroded hollow copper wire from the on-site system and strip the insulating layer on the surface of the copper wire; use a cutting machine to cut the hollow copper wire into specimens with a length of 2 cm; use a vernier caliper to measure the size of the flowing cross-section of the hollow copper wire, with a length of 7.11 mm and a width of 1.52 mm;

[0030] Place the copper wire specimens in a transparent heat-shrinkable round tube with a length of 8 cm and a diameter of 9.5 mm, and slowly heat from the middle to both ends of the specimens with a hot air gun so that the hollow copper wire is just encapsulated in the heat-shrinkable tube (when heating the area near both ends of the specimens, avoid overheating causing the heat-shrinkable tube to collapse). After encapsulation, tie both ends of the hollow copper wire specimens firmly with plastic ties;

[0031] 2) Assemble the dynamic cleaning test device

[0032] As Figure 1 shown, use a silica gel hose to connect the cleaning liquid water tank 2, the peristaltic pump 4, the corroded hollow copper wire specimen 5, and the cleaning liquid water tank 2 to form a circulating cleaning flow path. Place the cleaning liquid water tank in the heat-collecting type constant temperature heating magnetic stirrer 1, and there is a stirring magnetic bar 3 in the cleaning liquid water tank 2;

[0033] 3) Plot the Cu-EDTA complex concentration-absorbance working curve

[0034] Prepare an aqueous solution of disodium EDTA with a concentration of 0.6 g / L and a copper nitrate solution with a concentration of 20 mg / L (calculated based on the copper element content);

[0035] Prepare Cu-EDTA complex solutions with concentrations of 0, 2, 4, 6, 8, and 10 mg / L (calculated based on the copper element content) according to the following table

[0036]

[0037] Preheat the ultraviolet-visible spectrophotometer for 30 min. Use the ultraviolet-visible spectrophotometer to measure the absorbance of the six solutions in the above table at 265.6 nm, and record it as UV 265.6 ;

[0038] Perform linear fitting on UV 265.6 and the Cu-EDTA concentration, and the working curve obtained for the two is [Cu-EDTA] (mg / L) = 20.575 × UV 265.6 - 0.0951 (R 2 = 0.9997), where [Cu-EDTA] is the copper oxide content (calculated based on the copper element content);

[0039] 4) Conduct dynamic cleaning tests

[0040] Preheat the water bath temperature of the collecting heat type constant temperature heating magnetic stirrer to 30 °C; prepare 250 mL of 0.3 g / L disodium EDTA cleaning solution, and place it in the collecting heat type constant temperature heating magnetic stirrer to keep it at a constant temperature of 30 °C;

[0041] According to the size of the cross-sectional area of the hollow copper wire measured in step 1), control the linear flow rate of the cleaning solution on the copper wire to be 0.5 m / s, and calculate the required cleaning flow rate to be 324 mL / min; connect the corroded hollow copper wire specimen to the dynamic cleaning system, adjust the flow rate of the peristaltic pump to 324 mL / min, start the peristaltic pump, turn on the stirring, start the test and time; every 10 min, use a plastic straw to take about 4 mL of the cleaning solution, and after the cleaning solution cools to room temperature, use the preheated ultraviolet-visible spectrophotometer to measure the UV of the cleaning solution water sample 265.6 , and after the measurement, pour the water sample back into the cleaning water tank, and the total test time is 1 h;

[0042] Repeat the above steps and conduct tests under the conditions of 35 °C, 40 °C, and 45 °C respectively;

[0043] 5) Fit the apparent cleaning rate constant k

[0044] According to the working curve, convert the measured UV 265.6 into the copper content in the cleaning solution, and perform linear fitting on the test data, and the results are as Figure 3 shown.

[0045] From Figure 3It can be seen that as the temperature of the cleaning solution increases, the value of the apparent cleaning rate constant k increases, and the cleaning effect is better. Further, the activation energy of the reaction is calculated to be 60 kJ / mol using the Arrhenius equation. Thus, it can be known that the EDTA cleaning of corroded hollow copper wires is sensitive to temperature. Therefore, appropriately increasing the temperature of the cleaning solution can improve the cleaning rate.

[0046] Example 2

[0047] Different from Example 1, the method for evaluating the dynamic cleaning effect of EDTA on corroded hollow copper wires of a generator provided in this example mainly examines the influence of the EDTA concentration on the cleaning effect of EDTA on corroded hollow copper wires. The steps are as follows:

[0048] 1) Prepare specimens of corroded hollow copper wires

[0049] Take out the corroded hollow copper wire from the on-site system and strip the insulating layer on the surface of the copper wire; use a cutting machine to cut the hollow copper wire into specimens with a length of 2 cm; use a vernier caliper to measure the dimensions of the flow cross-section of the hollow copper wire, with a length of 7.11 mm and a width of 1.52 mm;

[0050] Place the copper wire specimens in a transparent heat-shrinkable round tube with a length of 8 cm and a diameter of 9.5 mm. Slowly heat from the middle to both ends of the specimens using a hot air gun so that the hollow copper wire is just encapsulated in the heat-shrinkable tube (when heating the area near both ends of the specimens, avoid overheating causing the heat-shrinkable tube to collapse). After encapsulation, tie both ends of the hollow copper wire specimens firmly with plastic ties;

[0051] 2) Assemble the dynamic cleaning test device

[0052] As Figure 1 shown, use a silicone hose to connect the cleaning solution water tank 2, peristaltic pump 4, corroded hollow copper wire specimens 5, and cleaning solution water tank 2 to form a circulating cleaning flow path. Place the cleaning solution water tank in a heating magnetic stirrer 1 with heat collection and constant temperature. There is a stirring magnetic stirrer 3 in the cleaning solution water tank 2;

[0053] 3) Determine the working curve of 265.6 the UV

[0054] Prepare an aqueous solution of disodium EDTA with a concentration of 0.6 g / L and a copper nitrate solution with a concentration of 20 mg / L (calculated based on the copper element content);

[0055] Prepare Cu-EDTA complex solutions with concentrations of 0, 2, 4, 6, 8, and 10 mg / L (calculated based on the copper element content) according to the following table

[0056]

[0057] Preheat the ultraviolet-visible spectrophotometer for 30 min, and use the ultraviolet-visible spectrophotometer to measure the absorbance of the six solutions in the above table at 265.6 nm, denoted as UV 265.6 ;

[0058] Perform linear fitting on UV 265.6 and the concentration of Cu-EDTA, and the working curve of the two is obtained as [Cu-EDTA] (mg / L) = 20.575 × UV 265.6 - 0.0951 (R 2 = 0.9997), [Cu-EDTA] is the content of copper oxide (calculated based on the content of copper element);

[0059] 4) Conduct a dynamic cleaning test

[0060] Preheat the water bath temperature of the heating magnetic stirrer with thermostat to 40 °C; prepare 250 mL of 0.1 g / L disodium EDTA cleaning solution, and place it in the heating magnetic stirrer with thermostat to keep it at 40 °C;

[0061] According to the size of the cross-sectional area of the hollow copper wire measured in step 1), control the linear flow rate of the cleaning solution on the copper wire to be 0.5 m / s, calculate the required cleaning flow rate to be 324 mL / min; connect the corroded hollow copper wire specimen to the dynamic cleaning system, adjust the flow rate of the peristaltic pump to 324 mL / min, start the peristaltic pump, turn on the stirring, start the test and time; every 10 min, use a plastic straw to take about 4 mL of the cleaning solution, and use the preheated ultraviolet-visible spectrophotometer to measure the UV of the cleaning solution water sample after the cleaning solution cools to room temperature 265.6 , and pour the water sample back into the cleaning water tank after the measurement. The total test time is 1 h;

[0062] Repeat the above steps and conduct tests under the conditions of EDTA concentrations of 0.2, 0.3, and 0.4 g / L respectively;

[0063] 5) Fit the apparent cleaning rate constant k

[0064] According to the working curve, convert the measured UV 265.6 into the copper content in the cleaning solution, and perform linear fitting on the test data. The results are as Figure 4 shown.

[0065] It can be seen from Figure 4 that as the EDTA concentration increases, the value of the apparent cleaning rate constant k increases, and the cleaning effect is better.

[0066] For the cleaning of the actual system, it is necessary to comprehensively consider the cleaning cost and the requirements for copper substrate corrosion, and select an appropriate EDTA concentration.

[0067] The above are only preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention. For those skilled in the art, it should be realized that all the solutions obtained by equivalent substitution and obvious changes made by using the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for evaluating the EDTA dynamic cleaning effect of corroded hollow copper wires in a generator, characterized in that, It includes the following steps: 1) Prepare a corroded hollow copper wire specimen; 2) Configure a series of concentrations of Cu-EDTA complex solution, measure the absorbance of the solution at 265.6 nm, and plot the working curve of Cu-EDTA complex concentration-absorbance; 3) Use the aqueous solution of disodium EDTA preheated to a certain temperature as the cleaning agent to dynamically clean the corroded hollow copper wire specimen. Collect the water sample of the cleaning solution at regular intervals and cool it to room temperature. Measure the absorbance of the water sample under the light of 265.6 nm. Calculate the copper content dissolved by cleaning according to the working curve, perform linear fitting on the copper content and the cleaning time. The slope obtained by fitting is the apparent cleaning rate constant, and the cleaning rate is quantitatively characterized according to the magnitude of the apparent cleaning rate constant.

2. The method for evaluating the EDTA dynamic cleaning effect of corroded hollow copper wires in a generator according to claim 1, characterized in that, In step 1), the preparation method of the corroded hollow copper wire specimen is as follows: Strip the surface insulation layer from the actual corroded hollow copper wire taken from the site, cut it into small sections, encapsulate the copper wire specimen with a heat-shrinkable round tube, and then tie the two ends of the specimen firmly.

3. The method for evaluating the EDTA dynamic cleaning effect of corroded hollow copper wires in a generator according to claim 1, characterized in that, In step 3), the dynamic cleaning method is as follows: Make the cleaning solution flow through the corroded hollow copper wire specimen at a certain flow rate to clean the specimen under simulated real cleaning conditions.

Images