The mechanism of corrosion of the copper wire of the generator by the internal cold water and the protection of Chen Shesheng (Yunfu Power Plant, Yunfu 527328, Guangdong), the key is to increase the pH value of the water, combined with field practice experience. Based on the results of trial and error and the accumulated experience and lessons learned from relevant domestic and foreign parties, a feasible anti-corrosion operation method and a nitrogen treatment method were proposed.

8:B Received M4.i*03£WaAcadcJocaalElElectronicPublishing Only when the l3n is increased to 7 when the copper oxide saturated solution is concentrated, China has a considerable number of online running generators using direct water cooling for cooling, and some use single The water is cold, and some are double-cooled. For its corrosiveness, a large number of experimental studies and field tests have been carried out at home and abroad, and many important factors affecting the corrosion of copper wires have been deeply understood and some corresponding preventive measures have been taken. Even so, in operation Corrosion accidents on the copper wire of the motor are still reported.

This paper will discuss the mechanism of copper wire corrosion and the corrosion protection of copper wire.

Corrosion mechanism of copper wire The material of copper wire of generator is generally copper. The corrosion rate is generally 0.002~0.05gAm2h without protection. Oxygen is the main corrosive agent. The content of carbon dioxide in water and the degree of corrosion of water Greater impact. Under the condition of P(2)=0.1~2mg/L and P(C2)=1, the dissolved oxygen interacts with copper to form an oxide film: these copper oxides will uniformly cover the copper surface, and its protective performance is better. Poor, can not prevent the further occurrence of the substrate corrosion process. During the corrosion process, the monovalent copper ions formed by the corrosion are oxidized by dissolved oxygen to divalent copper ions. When there is no special protective measure, the corrosion intensity depends on the oxygen concentration and the Cu2+ content.

However, when the generator cooling system is operating, the corrosion of the copper wire is related to the formation of copper oxide. The rate of formation of copper oxide depends on the content of copper ions, the pH of the solution, and the temperature.

In order to precipitate copper oxide in the solution, the Cu2+ concentration must be made higher than the solubility of CuO; otherwise, the oxide is dissolved. The copper oxide dissolution curve is as shown.

At the same time, the dissolution of copper oxide is buffered; further increasing the pH causes a sharp increase in solubility, and as a result, the formation of an anionic HCuOl in the solution, in practice, even when the concentration of Cu2+ may be the smallest, greatly exceeds the solubility of CuO, that is, all The actual solution is thermally unstable. Why is this happening? It should be said that Cu2+ exists in the colloidal state in the cold water.

In fact, the solubility of copper oxide is particularly affected by temperature. At pH<7, the solubility decreases sharply with increasing temperature; when pH>9, the equilibrium concentration of copper oxide in water shows a strong opposite characteristic. Solubility increases with increasing temperature; when 7<.8> 2 Factors affecting corrosion of copper wire When oxygen is saturated in water, the mass concentration of oxygen is 6 ~ 13mg / L; when water is in direct contact with air, the concentration of oxygen in water is dissolved gas, metal and salt oxide in water, and Other organic matter, these numerous impurities make the water conductive and corrosive to copper, which directly reflects the higher the conductivity and the stronger the corrosion. However, within a certain range, the increase in conductivity causes the rate of corrosion to accelerate less than the rate at which the conductivity is too low to cause corrosion to accelerate. The carbon oxide destroys the protection of the initial oxide layer, and the dissolution of the iSh addition body in water is accelerated. Generally, the temperature increases and the corrosion rate increases. For the generator of the closed isolation system, the temperature rises and the oxidation acts on the generator of the open system. On the one hand, the temperature rises to produce the above phenomenon, which accelerates the corrosion; on the other hand, the temperature rise causes the solubility of the gas in the water to decrease, and the corrosion is slowed down. . In an open system generator, when the temperature is raised from 30*C to 60*C, the corrosion gradually increases; the temperature continues to rise, and the corrosion gradually decreases, forming a so-called "intermediate large, two small" state.

23.3 Flow Rate The flow of cooling water has two effects: the higher the flow rate of water, the greater the mechanical wear. The data show that when the flow rate of cooling water in the electrolytic copper hollow wire is 0.2m/s, the monthly corrosion amount is about 0.7mg/cm2; when the water flow rate reaches 1.65m/s, the monthly corrosion amount can reach 2mg/cm2; When the flow rate of water exceeds 5 m/s, cavitation also occurs.

The actual wear of the motor is better than that of electrolytic copper. When the water flow rate is 3m/s, it takes 350 years, and the inner surface wear depth of the hollow copper wire reaches 0.15mm, which indicates that the hollow copper wire has a long life. In the design of the motor, the calculation of the water flow velocity is generally less than 2 m/s, and the mechanical wear caused by the water flow is not important compared to other corrosion.

The flow of water accelerates the migration of corrosive substances from the water to the metal surface and destroys the passivation film. A large amount of experimental data shows that the corrosion rate of copper will be large with the flow rate.

In water, the electrode potential of copper is lower than the electrode potential of oxygen. From the point of view of chemical thermodynamics, copper can be oxidized and etched. Whether the corrosion reaction proceeds continuously depends on the nature of the corrosion product. If it deposits on the copper surface very quickly and is dense, it protects the so-called protective film; on the contrary, the corrosion deposit can not form a protective film, and the corrosion will continue.

The formation and corrosion resistance of the copper oxide film is closely related to the pH of the solution. Increasing the pH of the medium reduces the solubility of copper oxide, but too high a pH causes CuO to be converted to CuO-2, which dissolves the protective film. In fact, the natural corrosion potential of copper in water is ~10, copper is in the most stable state, and the corrosion rate is the smallest.

Ammonia is a commonly used pH adjuster. However, since it may form a stable copper-ammonium complex with copper ions and accelerate the corrosion of copper, it is considered that ammonia has a large acceleration of copper dissolution when dissolved oxygen is present in the water, because of the formation of highly soluble tetraammine. The complex ion of copper 2. In fact, this understanding is one-sided. It has already been reported in practice, and the same research report is available in China. In the early years, there were reports on the treatment of copper pipes in condensate: when the mass concentration of oxygen is 10~650å’‹/L, the pH value of the condensed water is adjusted with ammonia. When the pH is 6.0 ~ 65, the loss rate of copper is 0.2 g Am2. Day) When the pH is 8.0 to 8.5, the loss rate of copper is 0.002 g Am2 day. When the mass fraction of ammonia exceeds 105, the loss of copper is significantly increased.

The experimental study with naval copper as an example confirmed that the corrosion resistance of copper was good at pH=8.0~9.5; the corrosion resistance of p27 was significantly decreased at p10; when the pH was raised from 10 to 11, the corrosion accelerated. From 2Wn per year to 2mm or more, plus a thousand times.

Only when the mass fraction of ammonia is large (more than 10-5), the corrosion is significantly increased. However, under the specific environment and conditions of the generator, due to the limitation of the conductivity control standard, the ammonia content may not be high enough to accelerate the corrosion of the hollow copper wire of the generator.

3 Anti-corrosion method For the treatment of cold water anti-corrosion in generators, there have been some reports at home and abroad, such as closed-type isolated water-cooling system, open water-cooling system, continuous hydration, continuous discharge, plus corrosion inhibitor treatment.

3.1 Closed isolated water cooling system In the system, a certain pressure of inert gas - nitrogen or hydrogen (hydrogen for the unit with hydrogen cooling system), so that oxygen and carbon dioxide can not enter the system, to prevent oxygen corrosion and carbon dioxide acid corrosion To a certain role. The condition is that the system must be tight, use deoxygenated decarburized water, and introduce an ion exchange system, so it is cumbersome to operate.

3.2 Open water cooling system Introduces the condensate of the steam turbine into the internal cold water system, and then cools the generator and returns it to the condenser. This is because the pH of the condensate is relatively high and is good for corrosion protection. However, people are worried that the addition of copper in the internal cold water will cause the copper content of the boiler water to increase, which will affect the safety of the boiler. When the water content of the water supply and the furnace water is increased, the corrosion of the water wall tube is accelerated. The reaction is as follows: Since there is a possibility of corrosion, it is necessary to pass the test to determine whether it is feasible to use the open water cooling system.

3.3 Continuous hydration, continuous discharge method i ammonia to copper corrosion is conditional. For this 1 point 611 foreign immigrants also supplement the way of containing ammonia) suspected water. The amount of water discharged is determined according to the conductivity and the continuous discharge and continuous copper content of some domestic power plants in the domestically cooled water system. The method is to overflow from the upper part of the inner cold water tank to achieve the purpose of reducing the copper content in the water. This method is simple to operate, but it does not actually have a preservative effect, and the amount of water is large, and it is difficult to control various indexes.

3.4 Adding Corrosion Inhibitors Some power plants in the former Soviet Union added some hydrazines to the closed water-cooling system. The mass fraction was (0.5~1)X10 3, the conductivity was controlled to a very low range, and the anti-corrosion effect was quite good. The antiseptic effect of hydrazine is self-evident, but it requires a system to be sealed, and the drug has a certain toxic effect on the human body, so it is not convenient to use, so it is not popular for application.

In the late 1980s and early 1990s, many domestic power plants used anti-corrosion treatment with MBT (2-thiobenzothiazole). The specific method is: dissolve MBT in NaOH solution to make mother liquor, and add to the inner cold water tank to maintain the mass concentration of MBT at 0.5~8mg/L. The conductivity is less than 10 yang/cm. Obviously, the following problem occurs: MBT is insoluble in water, and it is necessary to increase the conductivity of cooling water by adding NaCH. Secondly, MBT may precipitate and deposit on the inner wall of hollow copper wire, causing poor heat dissipation of copper wire or hollow. Copper wire blockage accident.

In the late 1980s and early 1990s, various power plants in Hunan Province added BTA+EA (benzotriazole + ethanolamine) to the anti-corrosion treatment in the cold water system of the generator, and received certain effects. The method is as follows: BTA is dissolved in an aqueous solution of EA, and added to an internal cold water tank to maintain a BTA initial mass concentration of 10-15 mg/L. The conductivity is less than 10 å’«/cm. Similarly, BTA is insoluble in water and relies on EA to dissolve. It is also easy to implement the same problems as adding MBT drugs.

4 Anti-corrosion measures of Yunfu Power Plant Yunfu Power Plant is now operating a domestic 125MW dual-water internal cooling generator set, which was put into operation in 1991. The chemical demineralized water has been added with ammonia at the outlet of the desalinated pump before being sent to the main plant. The amount of ammonia added is adjusted and controlled by the chemical personnel; the demineralized water can enter the internal cold water tank directly after entering the main plant; in addition, the modified boiler condensate It also has direct access to the inner cold water tank. Particular emphasis is placed on conductivity, not on pH and copper content, which is a common problem in many power plants. At the beginning, the plant also treated some of the internal cold water, but it was all passive. It was only taken to ensure the conductivity of the internal cold water was qualified. The pH value of the water was not qualified for a long time, and the mass concentration of copper was also long. Unqualified, sometimes as high as 1.2mg/L. Factory Water Vapor Supervision Guide, major changes have been made to the control index of the cold water inside the generator, in which the conductivity is changed from no more than 5å’«/L to no more than 10å’«/L. This creates conditions for increasing the pH. According to the above conditions and the previous analysis and research, combined with the specific situation, Yunfu Power Plant chose to increase the pH value by adding ammonia to the inner cold water to realize the anti-corrosion treatment of the hollow copper wire of the generator. It is verified by experiments that the theoretical research of the previous 2.34 is correct. During the test, in order to ensure the absolute safe operation of the generator set, the testers took a cautious attitude and controlled the conductivity between 2 and 6 å’«/cm, so the upper limit of the pH rise did not exceed 8.5. However, the conclusion was feasible.

Correlation curve. It can be seen that pH is closely related to the degree of dissolution of copper: when the pH is less than 7, the mass concentration of Cu2+ in water is less than 200å’‹/L in the qualified range; when pH>7.8 The mass concentration of Cu2+ in water is less than 50å’‹/L. When the pH is <64, the mass concentration of Cu2+ in water reaches 900Pg/L or more. Therefore, for the treatment of the cold water in the generator, in the case of ensuring the conductivity is acceptable, the pH value in the water should be increased as much as possible, at least to ensure that the pH is > 7.4.

5 Conclusions The key to improving the corrosion resistance of the generator cooling system is to increase the pH of the water. The method of adding ammonia to increase the pH value of the internal cold water has great advantages in terms of technology and economy: the medicine cost is low, the purchase is easy, the use is safe, the amount of demineralized water is saved, and the basis is stable combustion. One of the important factors.

3.4 Change the opening degree of the exhausted baffle. Under a certain number of rotating rods and a certain primary fan speed, randomly select two sets of burners, change the opening of the exhausted baffle, and measure the exhaust gas nozzle and the main gas nozzle once. Wind speed to investigate the relationship between the opening of the exhausted baffle and the speed of the main and spent nozzles. According to the measurement results, the flame stroke, ignition and fullness of the furnace are more reliably adjusted to the optimum state during the hot state adjustment.

3.5 Changing the number of the rotating rods Under a certain degree of exhausted baffle opening and a certain primary tube wind speed, two sets of burners are randomly selected to change the number of the rotating rods and measure the primary wind speed of the exhaust gas nozzle and the main gas nozzle. In order to investigate the relationship between the position of the derotating rod and the speed of the main and the spent nozzle. In the hot state, the position of the rotating rod is adjusted according to the quality of the coal, so that the main nozzle wind speed is more suitable and the fire point is controlled more effectively.

3.6 Furnace air distribution leveling furnace air distribution leveling, including the first and second wind leveling. Select the air distribution method, measure the wind speed in the furnace, check and level the burner air distribution, and ensure that the corresponding group burners have the same symmetrical wind speed at the exit of the baffle. This link is the basis for forming a good *W* type combustion mode.

3.7 Fireworks Tracer According to the principle of modeling, fireworks are fired and photographed to visualize the flow, mixing and expansion of the airflow in the furnace. Due to the symmetry of the *W* type flame boiler combustion system, several sets of burners can be randomly selected according to the test conditions to test the condition of the furnace, determine the furnace fullness, and evaluate the distribution method. When we carried out the cold test of No. 10 boiler in Shaoguan Power Plant, we designed the following test conditions: select a group of burners and select different primary wind and speed fireworks to check the penetration of the primary wind and the wind to the furnace. The effect of fullness and shape.

Select a group of burners to design a primary wind asymmetry or a corresponding secondary wind asymmetry, and observe the influence of the distribution asymmetry on the *W* shape.

Select a group of burners, change the air distribution mode of the secondary air, and observe the influence of the air distribution method on the shape of *W*.

Select a burner, change the position of the rotating rod, observe the airflow expansion and the main airflow penetration; change the position of the exhaust air baffle and observe the change of the main airflow and the running air penetration.

Fireworks are fired in the semi-furnace to check whether the overall aerodynamic field in the furnace is in good condition.

4 Conclusions * The main feature of the W* type flame boiler is that its combustion system is symmetrical. Therefore, the cold test should be designed around this feature, which can save manpower and material resources and reflect the hot state of the furnace more realistically; *W* type The cold test content of the flame boiler shall include static inspection, especially the concentricity inspection of the burner sleeve, and examine the degree of influence of the eccentricity on the primary wind stiffness; the cold test of the *W* type flame boiler shall be carried out in the furnace. Leveling, this is the basis for ensuring the *W* type of combustion method; in accordance with the test methods and contents discussed above, the cold state test can basically grasp the flow information in the furnace and can adapt to the thermal adjustment of the coal.

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