Analysis on leakage and maintenance of boiler valves in thermal power plant

Abstract : As an important part of the boiler system in thermal power plants, the safety of boiler valves has a very positive effect on the safe and stable operation of thermal power plants. This article gives a brief overview of the main causes of internal leakage and external leakage of boiler valves in thermal power plants in China, and then proposes preventive measures for valve leakage in thermal power plants. Based on this, the key points of valve leakage inspection in thermal power plants are focused on in order to focus attention on this. A person in the field provided some highly viable reference opinions to promote the vigorous development of China's thermal power generation business.
Key words: Thermal power plant; Boiler valve; Internal leakage; Safety valve maintenance With the development of China's national economy and the improvement of people's living standards, all sectors of society pay attention to the thermal power generation business in China, especially the leakage and overhaul of boiler valves in thermal power plants. The degree is getting higher and higher. In recent years, many new thermal power plants in China have adopted secondary reheating and new supercritical production technologies. Compared with common boiler valves, boiler valves in large-scale thermal power generating units have become more severe and urgently needed improvement. Its own safety and airtightness, to solve the problem of leakage of the valve, and enhance the efficiency of boiler operation in thermal power plants.
I. Boiler valve leakage in thermal power plants and their causes 1. Internal leakage of boiler valves in thermal power plants According to the location of valve leakage, the leakage of boiler valves in thermal power plants can be divided into internal leakage and external leakage. The internal leakage of the boiler valve in a thermal power plant can also continue to be refined into two forms: leakage of the root of the seal and leakage of the surface of the seal. The main reason for the internal leakage of valves in thermal power plants may be during the manufacture and installation of the valves. There is no reasonable protection measure. Impurities such as iron scraps and welding slag in the manufacturing materials block the valve core. The valve cannot be closed tightly, causing leakage inside the valve. In addition, it may be because the material selection of the valve sealing surface is not suitable, resulting in serious media corrosion problems, causing leakage and other failures inside the valve.
2. External leakage of boiler valves in thermal power plants In addition to internal leakage problems, boiler valves of thermal power plants may also have external leakage due to external factors. The main reason for the external leakage of the valve is that in the manufacturing process of the valve, a certain degree of manufacturing defects will inevitably occur, and problems such as blisters and slag inclusions will cause leakage outside the valve. In addition, if the valve packing material and the working medium cannot be fully adapted, the external pressure of the valve will be leaked to a certain extent due to the problem of the filling material under the conditions of increased working pressure, temperature, and corrosiveness of the medium.
Second, thermal power plant boiler valve leakage prevention measures 1. Optimization of thermal power plant boiler valve design and manufacturing process management standards In order to avoid thermal power plant boiler valve internal leakage and external leakage and other issues, from the boiler valve design and manufacturing, storage, transportation and construction and Installation and other aspects to increase management and control efforts to completely eliminate the leakage of the valve. In the process of valve design, it is necessary to design the valve structure, especially the sealing structure, according to the actual working conditions. For example, in the process of valve design for a boiler valve design and manufacturing unit of a thermal power plant in a certain region in China, in order to avoid leakage accidents, the sealing performance and the selection of materials are emphasized. The manufacturing unit in the region has selected a higher strength corrosion resistance. And high temperature materials, effectively enhance the valve's sealing and safety.
2. Increase the management of boiler valve storage and transportation in thermal power plants Whether it is the supply side or the purchase side of boiler valves, it is necessary to strengthen the storage and management of valves. Ensure that the warehouse environment is clean, the humidity and temperature need to be controlled within a reasonable range, and the impact of environmental factors on the quality of valve components should be reduced as much as possible. For example, in some regions of China, thermal power plant boiler valve production and manufacturing companies have strengthened the standardized management of warehouse environment in the link of valve storage, posted clear and eye-catching logos inside warehouses, and standardized the storage locations of parts and components of different specifications and models. The use of off-site storage effectively avoids the wear of boiler valve components. During the transportation process, the valve manufacturers in the region have focused on strengthening the loading and fixing work. When the valves are hoisted and unloaded, the lifting speed can be reasonably controlled to avoid damaging the valves due to external forces.
3. Strengthen management methods for construction and installation of boiler valves in thermal power plants Before formalizing the installation of boiler valves in thermal power plants, it is necessary to verify the specific models and specifications of different valves, and to check whether the fillers are substantial. And clean the welding slag and iron swarf to avoid clogging of the valve core with impurities. In the process of installation, it is necessary to strengthen the supervision of the standard operation of the staff, to avoid the construction and installation of technical workers to use the external force to violently impact the valve, do a good job of protection during the hot welding and thermal cutting, to avoid splashing and welding Material damages the valve seals. Install the boiler valve to select the appropriate equipment to avoid over tightening and cause serious damage to other sealing components such as flanges.
III. Analysis of Main Points for Maintenance of Boiler Valves in Thermal Power Plants 1. Inspection and Repair of Boiler Safety Valves in Thermal Power Plants The maintenance of boiler safety valves in ignition power plants requires starting from the valve seats, valve discs, and valve bodies and other components to inspect the valves for trachoma and cracks. In addition, the integrity of the valves, such as screws and bolts, needs to be checked to see if the straightness of the stem complies with the relevant manufacturing standards. For example, in a certain region of China's thermal power plant boiler safety valve manufacturer during the troubleshooting process of the safety valve, first disassemble the full-scale safety valve assembly, remove the cap, fork rod and handle, and finally the upper and lower end The adjustment lever is removed. And in the entire process of disassembly to do a good job of statistical records to ensure that all technical indicators are in line with the basic requirements of the design drawings. The safety valve maintenance test needs to be adjusted in order from high pressure to low pressure. When the internal pressure of the container reaches 70% of the rated pressure, the heat control room pressure gauge and the on-site pressure gauge need to be compared. If there is data entry and exit need to follow the heat The pressure gauge in the control room is the standard for debugging. Observe whether the boiler safety valve starts to jump when the pressure reaches the set pressure. After commissioning, ensure that the pressure is within 80% of the rated pressure, and you can put it into normal use.
2. Check Points for Boiler Check Valves in Thermal Power Plants Boiler check valves in thermal power plants in China are mainly divided into two types: springless and springless. To disassemble the spring-loaded check valve, it is necessary to remove the connection bolt between the valve body and the valve cover first, and then after 90° rotation, remove the valve cover and finally remove the valve flap and the spring. For springless check valve disassembly, the bolts can be removed and modified, and then the hexagonal ring is removed to remove the valve. For example, in the process of overhauling and maintaining the boiler check valve in a certain region of China's thermal power plant boiler safety management department, the inspection of the valve cover and the valve body is mainly strengthened to ensure that the valve cover and the valve body are free of cracks and trachoma. . Ensure that there are no impurities in the pipe joints inside the valve, unobstructed. The safety management department of boiler valves in thermal power plants in the area also tested the sealability of the check valve and the characteristics of the spring. Springs must not only be broken and rusted, but also need to ensure that the deviation of the verticality of each end of 100 mm can not exceed 1 mm, and the qualified valve components can continue to be used.
3. Check points for boiler regulating valve in thermal power plant The inspection and repair work for the boiler regulating valve in thermal power plant needs to focus on the presence or absence of grooves and pits on the surface of the regulating valve. For example, China's Inner Mongolia Datang International Tuoketuo Power Generation Co., Ltd., in the process of overhauling boiler regulating valves, deals with pits and grooves within 0.5 mm with coarse, medium, and fine grinding; Pits and grooves greater than 0.5 mm are eliminated by lathe processing. Thermal power companies in the region have also developed a scientific standard boiler control valve quality standard for inspection and management of boiler overhaul work. The regulations clearly state that the connection screw holes of the valve cover and the valve stem need to be kept in good condition, the degree of curvature of the valve stem needs to be within 1 inch of the full stroke, and the degree of ellipticity needs to be within 0.05 mm. In addition, there are a series of standards for managing the maintenance of internal boiler valves in thermal power plants, which have contributed positively to improving the power generation efficiency of thermal power plants in the region.
4. Check and maintenance of the boiler cut-off valve in thermal power plants The maintenance work of the boiler shut-off valve in the power plant needs to perform corresponding inspection standards according to the degree of wear of the sealing surfaces of the valve disc and the valve seat after dismantling. The service personnel of the boiler shut-off valve in the thermal power plant in a certain area in China pointed out that when there is a significant crack on the sealing surface between the valve disc and the valve seat, it is necessary to adopt a surfacing welding method to repair it. For the more serious cases, direct replacement seal can be adopted. The way to deal with. When the pit or groove depth of the sealing surface exceeds 0.5 mm, the same treatment method as the sealing surface of the regulating valve needs to be adopted, and the surface pit and the groove are eliminated through lathe machining. After the maintenance and adjustment of the valve maintenance department, the sealed surface of the boiler stop valve in the thermal power plant in the region is self-sealing and assembly, which can improve the efficiency of installation and closing of the electric device and the valve. After cleaning the connection assembly through the various parts of the valve body and the sealing surface Put in the corresponding part, you can complete the assembly. Ensure that the flexibility and quality of all parts are in compliance with the relevant standards. After the maintenance records are completed, they can be officially put into use.
IV. Conclusion In summary, in the face of leakage of boiler valves in thermal power plants, staff in related fields need to always adhere to the principle of quality first and prevention and management, and increase thermal power generation from design and production to all aspects of construction and installation. Plant boiler valve quality control. The overhaul of safety valves, check valves, regulating valves, and shut-off valves of boilers in thermal power plants shall be conducted to ensure that no safety problems occur in the use of boiler valves in thermal power plants, thereby minimizing potential safety hazards and providing firepower to our country. The continuous development of the power generation business makes a positive contribution.
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[2] Lian Hongxi. Analysis of Common Failures of Boiler Safety Valve Valves [J]. New Technology & New Products, 2015, (23): 180.
[3]LI Ruidong, LIU Yongqiang, MA Zheng. Preventive Measures for Valve Leakage of Boiler Steam System during Infrastructure Construction of Thermal Power Plants [J]. Inner Mongolia Electric Power Technology, 2011, 29(03):107-108.

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