Detailed explanation of the cause and control measures of the four-pipe leakage of the boiler

The main pressure-bearing pipes within the scope of the boiler body are the economizer tube, water wall tube, superheater tube, and reheater tube (hereinafter referred to as the "four tubes"), which are one of the important equipment of thermal power plant boilers, which are responsible for heating the water supply. , The important task of evaporating feed water, heating steam, and heating steam for work. In normal operation, if the "four tubes" of the boiler leaks, it will only be repaired by forced shutdown. The leakage seriously affects the normal production of thermal power plants and causes great harm to power plants and power grids. The direct economic loss is For hundreds of thousands or even millions of dollars, the direct and indirect losses of users due to tripping and power outages are even greater. The leakage of the "four pipes" seriously threatens the safety of the units of thermal power plants, and the hidden dangers of the "four pipes" are major hidden dangers of the units of thermal power plants.

In recent years, coal prices have risen and the cost of power generation has continued to increase. The survival of thermal power plants has been continuously impacted, and higher requirements have been placed on the safe operation of thermal power plants. Preventing the "four pipes" of the boiler from leaking is of great significance for improving the economic efficiency of the enterprise, establishing the image of the enterprise, and increasing the competitiveness of the enterprise.

1. Analysis of the cause of leakage of the four boiler tubes

1. Abrasion is one of the main reasons for the "four pipes" leakage of the boiler.

The mechanism of wear: The flue gas of the pulverized coal furnace contains a large number of fly ash particles. These fly ash particles have a certain kinetic energy. When the flue gas washes the heating surface, the fly ash particles will continue to wash the pipe wall, every time from the pipe Cutting off extremely tiny metal shavings over time will make the pipe wall thinner, which is wear.

There are many factors that affect the wear of the heated surface, mainly in the following aspects:

①Fly ash speed: the amount of wear is proportional to the third power of the speed of fly ash. Every time the flue gas flow rate doubles, the amount of wear will increase by 7 times.

②Fly ash concentration: the increase in fly ash concentration will increase the number of fly ash impacts and increase the wear.

③Characteristics of ash particles: the coarser the ash particles, the harder and the more severe the wear. An increase in the carbon content of fly ash will also increase wear, because the hardness of coke in the ash is higher than that of ash particles.

④ Fly ash impact rate: the fly ash particles are large, the specific weight is large, the flue gas flow rate is fast, and the flue gas viscosity is small, the impact chance of the fly ash will be more, and the wear will be serious.

2. High temperature corrosion is also an important reason for the leakage of the "four tubes" of the boiler.

High-temperature corrosion mainly occurs in the area of ​​the water wall of the furnace. The corroded parts are usually above and below the burner. The power plant with centralized primary air is more serious, and the pipe on the fire side of the water wall is more serious. The high temperature corrosion of the water wall is mainly due to the formation of a molten soot layer on the surface of the pipe, and the local high concentration of H2S has a great influence on the corrosion. Oxygen-deficient combustion in the boiler, a strong reducing atmosphere is formed in the main combustion zone, HCL aggravates the damage to the oxide film, the dynamic field of the furnace is not good, the diameter of the tangent circle of the air flow in the furnace is too large, and the air flow sticks to the wall. These are the reasons for the high temperature corrosion of the water wall to burst the pipe.

3. Unsmooth water circulation causes operational problems.

In power plant boilers, one of the common problems that cause four-pipe leakage is that the water circulation is not smooth. The fundamental reason is that the power plant stays at low load for a long time, so the water circulation is not smooth. There are many reasons for the low load of the power plant, which is mainly determined by the economic development status. At the same time, in the northern part of our country, because the water freezes for a long time, this will also cause the water wall to often be unsmooth. Because the water circulation is not smooth and has a very subtle phenomenon, it is also very difficult to find in the actual equipment maintenance process. Therefore, this problem will cause problems in the operation of the boiler to a large extent.

4. Mechanical damage caused by improper maintenance by maintenance personnel.

During the maintenance process, due to the negligence of maintenance personnel or improper use of maintenance tools, the metal surface was injured, and the strength was reduced, so that the equipment could not withstand the pressure of the medium, resulting in pipe bursts; during the maintenance, other pipes were accidentally injured when sawing the pipe without being injured. detect, or not treated; tube welded nor strictly according to the welding process without heat treatment or operation procedures are all well mechanical damage. As long as the maintenance personnel are responsible and supervise the repair, and deal with the damaged pipe in time, this kind of leakage can be completely avoided.

5. The boiler design is not scientific.

The unscientific design of power plant boilers is the key reason for the leakage of the water wall of the boiler. This is because under the action of huge pressure, the welding part of the water wall can easily cause leakage because it cannot withstand the huge pressure. Under normal conditions, the root cause of this phenomenon is that the boiler design is unscientific, and the specific weight of the cold water wall pipeline is not paid enough attention, which leads to a relatively large load at the suspension point, causing a suspension point to be unable to bear it. Pressure, which in turn causes leakage.

2. Control measures to reduce the four-pipe leakage accident

1. Improve anti-wear and anti-corrosion measures, and adopt new technologies and methods to increase the service life of equipment. For example, add anti-wear protective plates at the place where the economizer penetrates through the wall and on both sides of the wall, and supplement and perfect the anti-wear cover plate on the pipe to strengthen the anti-wear effect; the combustion area of ​​the water-cooled wall pipe, especially the welding joint position, is subject to high temperature corrosion Seriously, in order to prevent high-temperature corrosion, new anti-corrosion materials are used, and the previous anti-corrosion technologies such as aluminizing have been cancelled, and the problem of high-temperature corrosion at the weld joint position is also solved.

2. Strengthen operation management. Improve over-temperature monitoring during the operation of the heating surface, strengthen technical analysis of over-temperature phenomena, and strengthen technical guidance for operators. Operators are required to correctly handle the relationship between safety and efficiency, grasp information about coal, equipment, and operation methods in advance, and strengthen combustion adjustments. Strictly control the occurrence of excessive temperature rise and fall, over-temperature and over-pressure operation, and unstable combustion during the start and stop, hydraulic test and operation of the unit, and strengthen the supervision of water and coal quality. It is recommended that all factories carry out over-temperature statistics and incorporate over-temperature and air-drop monitoring of steam temperature into the metal technology supervision system in order to strengthen technical supervision and management.

3. Strengthen boiler inspection and anti-wear and explosion-proof inspection. For the economizer, focus on checking the location of the flue gas corridor that is likely to cause wear; check whether the deflector, wear cover, anti-wear tile are intact and the pipe exhaust; check the pipe wear after the flue gas damper temperature control device. For the water wall, check the high temperature corrosion and thinning of the water wall near the burner; check the fin weld, pipe diameter expansion and fouling of the water wall, and leave a certain amount on both sides of the fins between the two medium temperatures. Expansion margin. For the superheater and reheater, check the fillet weld joints with the short header pipe joints, and improve the structure if the structure is obviously unreasonable; check for overheating such as scaling, high temperature oxidation corrosion and pipe diameter expansion in high load areas Phenomenon: whether the tube row positioning and clamping tube is loose; on the heating surface of the convection zone, check the tube wall wear that may form the flue gas corridor and the ash concentration area. The irregular or out-of-line tube must be eliminated and rectified. Check whether the pipe near the soot blower is damaged; whether the positioning screw of the desuperheater or the root of the flute-shaped spray pipe is cracked.

4. Actively train maintenance operators. Excellent boiler maintenance operators can effectively reduce the probability of boiler leakage in power plants. Therefore, the power plant must actively provide scientific and reasonable training for boiler maintenance personnel, so as to improve its technical level of maintenance and repair of power plant boilers, and enhance the maintenance technical operation ability of boiler maintenance personnel. Under normal conditions, it is necessary to hire highly qualified technicians with rich experience and superb skills to carry out technical training and explanations for boiler maintenance personnel. When conditions permit, the power plant can also actively cooperate with relevant colleges and universities, so as to use the rich resources of colleges and universities to improve the practical experience and theoretical level of maintenance operators.

5. Improving the design and appropriately increasing the safety margin during the design are the fundamental measures to prevent the "four pipes" from leaking. If reasonable consideration is given to the layout of the heating surface, the thermal strength of the furnace, the steel, the cross-mixing and the expansion system, etc., the occurrence of explosion leakage will be greatly reduced. For example, in recent years, more domestic imported 300MW units and 600MW units have been put into production. In the design, the manufacturer has made modifications to the boiler design, such as increasing the furnace height, selecting a lower furnace volume heat load, increasing the steel grade, and increasing the temperature reduction. The number of stages and points and the reduction of the smoke speed on the heating surface of the tail, etc., therefore, they have relatively few bursts.

3. Conclusion

In the safe production process of thermal power generation, the safe operation of boiler equipment plays a decisive role. Due to the leakage of the four boiler tubes and tube burst accidents, the boiler must be shut down to eliminate the shortage. Therefore, the safe operation of the four boiler tubes is the top priority of the safety production of the entire power plant. There is no shortcut to the boiler four-tube inspection. Only by investing a lot of manpower, material and energy, and adopting the attitude of compulsory repair and repair, can the safety of the boiler four-tube equipment be guaranteed. Although four-tube leakage is difficult to completely avoid for power plant boilers, it is possible to minimize the four-tube leakage by taking preventive measures. After mastering the basic law of four-pipe leakage, taking targeted measures can greatly improve the reliability of boiler operation.

In addition, the valves installed on the pipeline must also be of reliable quality.

Such as high pressure high temperature check valve