Analysis on Pressure Sealing Technology of Regulating Valve in Thermal Power Plant
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[Keywords] thermal power plant, control valve, pressure seal, leak out. CLC number:S259 Document code:A Article ID:1009-914X(2018)16-0075-01
1 Adjust the form and factors of the valve leakage 1.1 Adjust the leakage of the valve packing and the reasons for the adjustment During the operation of the valve, there is relative movement between the valve stem and the packing, which includes rotation and axial movement. With the increase in the number of switches, the number of relative movements also increases, as well as the effects of temperature, pressure, and characteristics of the fluid medium. Adjusting the valve packing is the most likely to leak. It is caused by the gradual weakening of the contact pressure of the filler, the aging of the filler itself, and the loss of elasticity. At this time, the pressure medium will leak out along the contact gap between the packing and the valve stem, and will blow out part of the packing material for a long time and flush the valve stem out of the groove mark, thereby expanding the leakage.
1.2 Leakage Adjustment of Flange The flange sealing of the valve is mainly based on the pre-tightening force of the connecting bolts, through the gasket to achieve a sufficient sealing specific pressure, to prevent the leakage of the sealed pressure fluid medium. There are many reasons for its leakage, the sealing gasket's pressing force is insufficient, the roughness of the joint surface does not meet the requirements, gasket deformation and mechanical vibration will cause the sealing gasket and the flange joint surface to leak. In addition, when the bolts are deformed or extended, the gaskets are aged, the resilience is reduced, cracks, etc., can cause the flange surface to leak tightly. Flange leakage also can not be ignored that the factors, such as biasing the gasket, so that the local seal than the pressure less than the excessive force, exceeding the design limit of the gasket, and the flange fastening process uneven force or flange Displacement of the center line, resulting in false tightness, etc., are prone to leakage. Leakage of the valve body and cause of leakage The main cause of leakage of the valve body is caused by casting or forging defects in the production process of the regulating valve, such as blisters, air holes, cracks. Etc., and fluid medium scouring and cavitation are also common causes of valve body leakage.
2 Principles and advantages of pressure seals 2.1 Principle of pressure seals The principle of pressure seals is based on the principle of the sealing mechanism of liquid materials under dynamic conditions. The method is to install special equipment on the leaked part, use a chamber formed between the sealing part and the special equipment, and inject the sealant into the chamber with a special high-pressure injection glue tool, and fill the whole chamber, so that the sealant squeezes force. With the pressure of the leaking medium balanced, a new sealing structure was established to block the passage of the leaky pores and to block the leakage of the medium.
2.2 Advantages of Pressure Seals (1) There is no need to shut down or isolate the system.
(2) There is no need to depressurize the system.
(3) Save a lot of energy and manpower.
(4) The power loss caused by equipment isolation or shutdown is greatly reduced.
(5) Reduced social and economic losses.
3. Several common leakage pressure sealing methods introduced According to the specific conditions of the power plant production site, you can replace the regulating valve, replace the valve packing, replace the flange gasket or repair welding holes to eliminate the general leakage. However, in the case of inability to isolate the regulating valve during production, corresponding technical measures must be taken to eliminate the leakage, so as to ensure the normal operation of the unit's safe production.
3.1 The pressure sealing treatment of the leakage valve of the power plant regulating the leakage of the filling chamber of the power plant is a safe and reliable technical means. The special fixture and the hydraulic injection tool are used to inject the sealant outside the fixture and leak part. The sealed cavity formed on the surface rapidly compensates for various complicated leaking defects. When the pressure of the injection agent is greater than the pressure of the leakage medium, the leakage is forcibly stopped, and the injection agent itself is converted from a plastic body to an elastomer in a short time, forming an elastic sealing structure and maintaining a certain working pressure ratio. To achieve the purpose of resealing. At present, the sealed injections produced and used at home and abroad are broadly classified into two types: one is a heat-cured sealing agent, which is suitable for dynamic sealing operations at room temperature, low temperature, and high temperature. These types of sealing agents are mostly made into rods. The solid or two-component greasy material, after being installed in the high pressure injection gun, has good injection processability and filling property under a certain pressure, without losing the function of adjusting the valve switch. Here are two commonly used methods:
(1) When adjusting the wall thickness of valve stuffing box is more than 8mm, when using injection type pressure sealing to eliminate defects under dynamic conditions, you can directly open the injection hole in the wall of the packing box of the adjustment valve. It is the stuffing box itself that regulates the valve. The effect of the sealant injected into the packing box of the adjusting valve on the packing is the same. First, adjust the position of the outer wall of the valve stuffing box with a hole of 10.5mm or 8.7mm in diameter. The hole can not be drilled through, leave about 1-3mm, pull out the drill bit, tap with M12 or M10 taps, tapping end After that, screw the injection special plug valve into the open position, and use the long rod drill with 3mm diameter to drill through the remaining adjustment valve stuffing box, then the leakage medium will be blown out in the direction of the drill bit cutting. In order to prevent the high-temperature, high-pressure toxic or corrosive medium from injuring and hurting people during drilling, a baffle can be used before the drill hole. First, drill a hole with a diameter of 5mm on the baffle to make it able to On long bits, there is no danger of adding the remaining wall thickness. Drill through the hole to remove the drill bit, turn the special injection plug valve to the off position, and cut off the operation of the medium connecting the high pressure injection sealant. If the media pressure in the packing box of the adjusting valve is low, a long drill with a diameter of 3 mm can also be used to drill through the small holes directly, and then a sealed injection agent operation operation is performed.
4 Conclusion There are pressure seals on other parts of the power plant production site. If we can grasp some basic seal knowledge, it will greatly help the economic improvement of the power plant. Only 200MW units start and stop once, and the direct economic losses amount to more than RMB 300,000. Therefore, we can successfully seal the on-site leaks and reduce the number of unplanned shutdowns. The benefits are significant. In short:
(1) Pressure seal is a kind of emergency repair work. Leakage point with pressure sealing treatment is a temporary treatment measure with certain limitations and timeliness. Under conditions, it is still necessary to overhaul the leak. The basic method to eliminate the phenomenon of "running, running, dripping, and leaking" at the scene and improve the health level of equipment operation is to rely on the rationality of planned maintenance and improve the equipment maintenance and repair process.
(2) Sealing with pressure is a highly specialized technology that requires on-site resilience of operators, and has high requirements for the mastery of mechanical expertise and the use of special tools for pressure sealing. Due to the high requirements for operators and special equipment, the promotion of this technology in thermal power plants has certain difficulties. At present, the on-site pressure sealing work is completed by some professional companies.
(3) Pressure sealing is a relatively new technology. It also has a process of continuous improvement and improvement. It has its own limitations and scope of application. Sealing with pressure does not solve all leakage problems. It is still in the stage of exploration and improvement.
References [1] Lu Yanxi. "Public Power Station Manual Valve" - ​​China Electric Power Press, 2000.5.