The controller teaches you to cope easily with the leakage of the regulating valve in the oil refining unit

The controller teaches you to cope easily with the leakage of the regulating valve in the oil refining unit

/
Abstract: The selection of regulating valve is a very meticulous work, not only to have a solid professional theoretical knowledge, but also have rich practical experience.
Good selection is not only beneficial to adjust the PID parameters of the control loop setting, so that the adjusted parameters get better control effect, but also make the service life of the valve increase.
This paper briefly introduces the composition and selection method of regulating valve. Key words: regulating valve composition classification selection Instrument control you teach easy to cope with the oil refining unit regulating valve leakage
Introduction: Regulating valve is an indispensable part of the petrochemical refining device, the use of regulating valve variety, large number, chemical production medium is corrosive, toxic or flammable and explosive, when regulating valve leakage, not only will cause serious waste of raw materials, energy and products, but also cause serious impact on the environment, and even cause serious safety accidents. Therefore, we talked about the leakage of the regulating valve in the petrochemical production process.
1. Cause analysis of leakage of regulating valve
Normally, there are two ways to adjust valve leakage, namely external leakage and internal leakage. In the following content, the author makes a detailed analysis of the reasons for the external leakage and internal leakage of the regulating valve.
Cause analysis of 01 control valve outside leakage
The cause of valve body leakage: the valve body is usually cast, easy to form sand holes and other casting defects, the sand holes on the valve body will lead to the leakage of the medium, the leakage is generally manifested as leakage, flow is small, through the hydraulic test can be found.
Reasons for valve stem leakage: Improper design and material selection of the valve stem will cause the valve stem to be stuck in a certain position, so that the valve can not be closed or closed loosely, resulting in medium leakage.
The reason for the leakage of the valve body connection: we often say that the sealing of the valve body connection part actually refers to the connection and sealing between the valve body and the valve cover. Usually, the sealing mode between the valve body and the valve cover is flange connection sealing; However, when the nominal diameter of the regulating valve is relatively small, it is necessary to adopt the threaded connection sealing way. In these two sealing methods, if the type of gasket is unreasonable, the quality of the material is not up to standard, the size of the material is not in line with the sealing requirements, and the processing quality of the flange sealing surface is poor, the tightness of the thread connection and the tightness of the bolt are not enough, and other reasons can cause the oil and gas leakage phenomenon in the connection part of the valve body.
02 Reason analysis of internal leakage of regulating valve door
The reason for the internal leakage of the regulating valve is that the regulating valve is not closed tightly, which generally occurs in the sealing surface of the seat. The specific reasons for internal leakage of the regulating valve are as follows: There are some problems in the design of the regulating valve structure and the production of the valve and the construction technology, such as the size of a component in the valve structure when there is a certain error, and the error exceeds the allowable range of the production process, which leads to the sealing of the regulating valve is not tight, resulting in the small flow of the medium in the device continuous leakage phenomenon.
In addition to the errors and problems in the design and production process of the valve, the causes of internal leakage of the regulating valve door also include the deformation of the sealing surface of the valve seat, the valve seal is not strict, which leads to the medium leakage problem of the refining unit. The medium leakage problem caused by the deformation of the sealing surface of the valve seat is mainly manifested as leakage. In addition, if the oil refining unit is loaded with a small amount of solid impurities in the medium, it can also cause the regulating valve to close loosely, resulting in the leakage of the regulating valve, and the leakage problem caused by the solid impurities contained in the medium, the form of leakage is also leakage, but the discharge of the flow may be small, it may be large flow.
Two, to prevent the regulation valve leakage countermeasures
Optimize the selection of valve design
The control and prevention principle of regulating valve leakage is mainly to take a series of effective measures to reduce the leakage degree of regulating valve as far as possible and reduce to a relatively low, to extend the good service life of the purpose. The reduction and reduction of the medium leakage of the regulating valve, the extension of the service life of the medium in the refining unit, the improvement of the utilization rate of the medium, to a large extent depends on the reasonable design and selection of the regulating valve, the quality of the valve product quality, the superb level of the valve installation and construction technology and the correct selection of the valve seal form. In short, if we want to solve and control the leakage problem of the regulating valve, we must first consider the optimization of the design and selection of the regulating valve.
The optimization of regulating valve design and selection involves the selection of regulating valve form, the design and manufacture of regulating valve itself, and the selection of regulating valve materials. When choosing the form of regulating valve, it should be optimized from the Angle of the requirements of process conditions and design specifications. The use of regulating valve, medium temperature, pressure, flow rate, pressure drop and corrosion of the medium, all directly affect the selection of regulating valve, but also according to the temperature and corrosion of the medium, choose the materials used in manufacturing regulating valve. According to the construction and actual operation experience, in addition to meeting the relevant process requirements and design specifications, the selection of adjusting valves should also be fully considered in various specific situations, so that it can match the operating conditions as far as possible, and meet the use requirements to a greater extent.
02 Packing box leakage countermeasures
The traditional soft packing seal is achieved by the radial contact stress generated between the stem and the packing and between the packing and the side wall of the packing box by the axial pressure of the packing gland. Therefore, the axial force of the gland must be quite large, which leads to the increase of friction torque between the packing and the valve stem, the increase of wear, and the fast wear of the soft sealing packing. Therefore, the gland bolt must be tightened frequently or the packing must be replaced to ensure a better sealing effect.
The suitable packing seal and packing seal combination can improve the reliability of regulating valve and prolong its service life. For example, the combination of flexible graphite ring packing is better than that of only flexible graphite ring packing. At present, the use of single flexible graphite ring filler is more in China. In foreign countries, the use of flexible graphite ring packing combination has become popular and achieved good results.
03 Eliminate leakage of valve body connection
The valve body connection part is sealed, in terms of its sealing nature is static seal, which should meet the following requirements: can adapt to the rapid change of temperature and pressure; Multiple disassembly without damaging the sealing element; Simple structure, compact, less metal consumption; Not sensitive to vibration and impact loads; It can meet the requirements of various working media.
The connection part of the valve body is usually sealed by birch groove or concave and convex flat gasket. In recent years, the “O” sealing ring has also been applied. Zen groove type flat gasket seal, is the flat gasket installed in the closed groove, this structure on the sealing surface, can produce a high sealing pressure, usually far beyond the yield limit of the gasket material, so as to ensure reliable sealing. It is suitable for medium and high pressure regulating valves with pressure greater than or equal to 4.0MPa. The disadvantage of this sealing structure is that when removing the regulating valve, the gasket is difficult to take out from the sealing groove. If it is rigidingly removed, the gasket will often be damaged.
Concave and convex type flat gasket sealing, is the flat gasket installed on the concave and convex flange sealing surface, compared with the camphor groove type flat gasket sealing structure, has the following advantages: when disassembling the adjustment valve, the gasket is easy to take out; Because the sealing groove is a step shape, so the processing performance is better.
According to the process parameters and fluid properties, aluminum, copper, 1Cr18Ni9Ti and rubber asbestos board can be selected as the material of flat gasket. Fluorine plastic is also a commonly used gasket sealing material, but because of its cold flow, if the seal structure is not designed properly, it will lead to adverse consequences.
“O” sealing ring, its simple structure, convenient manufacturing, as long as the seal structure design is reasonable, after assembly can produce enough radial extrusion deformation, can be achieved without axial loading, therefore, the flange connection sealing, can reduce the size of the flange structure, thereby reducing the weight of the valve regulation.
04 Valve stem leakage countermeasures
Valve stem is an important component of the valve, it is mainly used for transmission, to achieve the valve switch and regulation. Because the valve stem in the valve opening and closing process to act as the role of moving parts, force parts and seals, so it must have a certain strength and toughness to meet the requirements of the valve opening and closing, and assist the valve to play its regulating role. Generally speaking, the selection of stem materials will use some corrosion resistant medium, packing and other substances, and the process performance is better. And in order to further improve the friction resistance and corrosion resistance of the valve stem, the staff will also strengthen the surface of the valve stem to prevent the impact and corrosion of the valve stem by the medium, so that the leakage of the valve stem can be effectively controlled.
conclusion
In order to completely solve the leakage problem of the regulating valve in the refining unit, the primary countermeasure is to optimize the selection of the regulating valve design, and then control the leakage phenomenon of each part of the regulating valve. Only in this way can we effectively solve and control the leakage problem of the regulating valve, prevent the leakage of the medium, and achieve the purpose of improving the utilization rate of the medium.


Post time: Dec-02-2022

Send your message to us:

Write your message here and send it to us
WhatsApp Online Chat !