As we all know, in the production of petrochemical industry, rotating equipment is a very important part. Its normal and effective operation plays an important role in the whole production system. But in actual production, because

 

There are numerous events that affect production due to the failure of rotating equipment. Some data show that in this kind of fault, especially the leakage caused by seal failure is the main form, accounting for more than 50% of the total fault. Therefore,

 

It is of great significance to solve the history of the development of various types of seals and the factors of use, and to analyze and study the problem of seal leakage, which is of great significance to reduce the failure rate and ensure the safe operation of the device.

 

1. Packing seal

 

Packing seal, also known as compressed packing seal, commonly known as packing, English derived from the word Packings. Filler seal is one of the oldest forms of sealing, China's ancient water lifting machinery on the use of filled cotton yarn

 

Methods to plug leaks, early steam engines also used this form of sealing. In the 19th century, in order to adapt to the development of large-scale exploitation of petroleum energy technology, packing seal materials also have a new development.

 

exhibition. After entering the 20th century, due to the simple structure, low cost and wide adaptability of the packing seal, it is widely used in various static stuffing box seals and rotary reciprocating seals in petrochemical production.

 

And the sealing of the valve stuffing box, etc.

 

With the advancement of science and technology, engineering has put forward higher requirements for packing seals, and for decades, the continuous advent of new materials has provided the possibility for the development of new sealing fillers. Faced with a wide variety

 

Sealing packing, how to choose to adapt to different working conditions of the material is a new problem of great value. The following will introduce the common sealing filler, and provide the use status of typical petrochemical enterprises.

 

 

Figure 1: Petrochemical Source: Network

 

1.1 asbestos filler

 

Due to the long history of asbestos filler, the application experience is very mature, and the price is relatively low. However, due to the many inherent weaknesses of asbestos materials: high temperature water loss, fiber penetration, friction system

 

The number of large, so that asbestos filler will often produce seepage leakage, need frequent maintenance in use, and asbestos seasoning service life is relatively short, the pump shaft, valve stem wear is also relatively large and open

 

Start the trouble. The asbestos filler has a maximum temperature resistance of 450 ℃ and a maximum pressure resistance of 6 MPa. In actual production, it is generally used in parts where the temperature is lower than 200 ℃. Most of them are placed at both ends of the expanded graphite filler for compacting.

 

Sealed.

 

1.2 flexible graphite packing ring

 

Flexible graphite packing ring, also known as expanded graphite packing ring, has a relatively short history of use of asbestos packing ring. In the late 1970 s, China began industrial production, due to the flexible graphite packing ring.

 

It has excellent characteristics, so it quickly replaces the asbestos filler, especially in the original asbestos filler is difficult to seal well. Flexible graphite packing ring for a wide range of applications, good sealing performance, service life.

 

Long life, easy maintenance. Its disadvantages are low strength and numerous specifications. At present, petrochemical production is mostly used in "single flexible graphite", that is, pure flexible graphite packing ring. Pure flexible graphite fill

 

When the material is used, both ends should be braided filler or metal retainer to prevent extrusion.

 

1.3 carbon fiber filler

 

Carbonized fibers are manufactured by oxidizing man-made fibers such as acrylonitrile at a certain temperature, and the carbonized fibers are carbonized at a high temperature to become carbon fibers. Carbon fiber was successfully developed in the 1960 s,

 

And in our country as a large number of sealing filler is used in the late 1990 s. At present, the most used filler is carbonized fiber impregnated PTFE woven filler, which is very important for acid,

 

Alkali and organic solvents, such as the vast majority of media have good tolerance, while the coefficient of thermal expansion is small, good thermal conductivity, good self-wetting, so its applicability is quite wide, especially suitable for high-speed pumps.

 

1.4 PTFE packing

 

The advantage of PTFE is resistant to almost all known media, and is not easy to age, good self-wetting; and the disadvantage is that the thermal conductivity is small, the thermal expansion coefficient is large, so the use of high-speed pumps will make the friction production.

 

accumulation of raw heat. When the temperature reaches 200 ℃ and the linear velocity of the shaft is greater than 3. 5 m/s, the PTFE will soften and stick to the shaft, resulting in seal failure. To eliminate this shortcoming, the U.

 

A company has developed a woven packing containing graphite polytetrafluoroethylene, which improves the poor thermal conductivity of polytetrafluoroethylene, so that it can be used in high-speed pumps.

 

1. 5 Aramid braided packing

 

Aramid is a man-made fiber, according to its composition can be divided into several different types, as the filler used is a bright yellow para-aramid. The advantage of this fiber is high strength, the same quality of the fiber.

 

The strength is five times that of ordinary steel, and it is quite wear-resistant; it has good thermal stability, and it starts to decompose above 427°C; its thermal expansion coefficient is small. Aramid braided filler is woven with this fiber

 

Dip PTFE emulsion. It is particularly suitable for the sealing of mud pumps or other rotating equipment containing granular media.

 

 

Figure 2: Chemical Petroleum Source: Network

 

2. Mechanical seal

 

Although after years of development, packing seal has been widely used and constantly updated, but with the increasing requirements of environmental protection, at the same time, the sealing medium is also more and more complex.

 

The packing seal has not been well adapted to the sealing requirements of some equipment, so the mechanical seal has gradually replaced the packing seal on the stage of history.

 

As a sealing device, the main advantages of mechanical seals are reliable work, small leakage, long service life, and low power consumption. Therefore, they are used in pumps, mixers, compressors, centrifuges, reactors, and turntable towers.

 

And filter and other process equipment has been widely used. According to data, about 95% of the rotating equipment in the foreign petrochemical industry uses mechanical seals.

 

2. 1 History of mechanical seals at home and abroad

 

The earliest mechanical seal appeared in the United Kingdom in 1885, when it appeared in the form of a patent, and it was not officially applied until 1900. The structure of the end face mechanical seal that appeared at that time was very simple.

 

single, but also solved the problem of shaft sealing in the machine manufacturing industry at that time. Compared with the usual packing seals at that time, mechanical seals are advanced both in principle and function.

 

Sex. However, due to the lack of suitable materials and processing technology, although mechanical seals have many advantages, they are still not widely used. Until 1920, due to new technologies and new materials

 

The mechanical seal is gradually used more in the refrigeration device. After 1930, mechanical seals began to be used in large-scale shaft seals for internal combustion engine water pumps.

 

After the Second World War, mechanical seals developed by leaps and bounds in the United States. In the middle of the 20th century, due to the development of petrochemical technology, graphite, ceramics, carbide and other new materials in

 

The application of mechanical seal manufacturing and the improvement of processing technology control level, a new type of balanced mechanical seal and intermediate ring seal appeared in the late 1950 s. In the early 1960 s, due to the needs of the nuclear industry

 

hydrodynamic seal and hydrostatic seal appeared. In the early 1970 s, due to the special requirements of aerospace and nuclear power, new types of multi-stage seals and new types of silicon carbide and carbon graphite appeared.

 

Materials. In the 1980 s and 1990 s, with the continuous improvement of people's awareness of environmental protection, mechanical seals with the goal of "zero leakage" appeared; at the same time, some technicians developed on the basis of the principle of fluid dynamic pressure sealing.

 

A new type of thermal fluid power wedge mechanical seal and upstream pumping mechanical seal.

 

Since the beginning of the new century, with the gradual maturity of sealing technology, researchers have focused not only on the development of new types of mechanical seals, but also on the failure analysis and maintenance of specific rotating machinery.

 

At the same time, with the development of computer simulation software, there have been many studies on simulation analysis.

 

 

Figure 3: Petrochemical Source: Network

 

The application of mechanical seal technology in China started late. After the founding of New China, Lanzhou Refinery, Shenyang Water Pump Factory and other units took the lead in trial-producing mechanical seals for pumps in 1965. Tianjin Machinery before 1966

 

Seals factory began to produce mechanical seals. Before 1970, the scientific research, production, and use units under the Ministry of Machinery Industry, the Ministry of Petroleum, and the Ministry of Chemical Industry transferred scientific research personnel to form a joint design team.

 

Examination of foreign advanced technology, the joint design of the "series of mechanical seals for pumps".

 

In 1975, the Ministry of machinery industry approved the promulgation of the "pump mechanical seal standard". In 1978, the Ministry of Chemical Industry approved the promulgation of the "kettle with mechanical seal standards." In order to improve product quality, accelerate sealing technology

 

After 1980, advanced technologies from Britain, the United States, Germany, Japan and other countries were introduced one after another. Through tackling key problems and digestion, mechanical seals were made in terms of varieties, materials, technical parameters, etc.

 

Raised to a new stage. In 1993, the state promulgated the national standard "GB/T14211-1993 Mechanical Seal Test Method". In 1999, the State Administration of Machinery Industry revised the "Mechanical Seal Technology".

 

The classification method of mechanical seals provides a guarantee that mechanical seal products are close to the advanced level of foreign countries.

 

2. 2 Application Technology of Mechanical Seal

 

In more than a century, along with the continuous understanding of the mechanism of mechanical seals, people have successfully designed and manufactured all kinds of new mechanical seals, and applied them to petrochemical, power generation, aerospace

 

and the nuclear industry. At present, the application technology of mechanical seal mainly includes surface modification technology, combined sealing technology and controllable mechanical seal technology.

 

2. 2. 1 Surface modification technology

 

The so-called surface modification technology refers to the technology that improves the lubrication condition between the end faces by slotting the end faces of the seal, so as to realize the long-term operation of the mechanical seal [9]. According to the different depth of the slot, can be divided

 

There are two types of deep grooves and shallow grooves.

 

Open deep groove refers to a groove with a depth of millimeter (usually 1~2mm) on the end face of the mechanical seal. According to the different sealing principles, the end face deep groove mechanical seal can be divided into hydrostatic mechanical seal and

 

Thermohydrodynamic wedge mechanical seal.

 

Shallow groove refers to the opening of micron-level grooves on the end face of the mechanical seal, relying on the relative movement between the end faces of the seal and the step and conveying effect of the groove, thereby generating fluid dynamic pressure, and then balancing the closing force,

 

The non-contact sealing of the end face is realized. The more advanced dry gas seal and upstream pumping seal are mechanical seals with shallow grooves on the end face. Mechanical seals with shallow grooves can be used for gas or liquid media.

 

2. 2. 2 Combined sealing technology

 

With the rapid development of modern industry, high temperature, high pressure and the emergence of a variety of new media, industrial production of sealing requirements are also getting higher and higher, many times a single seal is difficult to meet the harsh

 

condition. Therefore, people combine several seals and make full use of the inherent advantages of all kinds of seals to make them play a full role, and the combination seal arises at the historic moment.

 

Although there are many forms of combined sealing, its essence is nothing more than non-contact sealing and contact sealing combination and contact sealing and contact sealing combination. In combination seals, mechanical

 

Sealing is mainly used to prevent leakage, while other forms of sealing are mainly used to throttle the role of block.

 

It is an important technical development trend to replace the traditional floating ring seal with mechanical floating ring combination seal in medium and low pressure process gas compressor. According to data, after the 1970 s, it was introduced from abroad.

 

In the large-scale petrochemical plant, the proportion of mechanical-floating ring combination seal is increasing, and the scope is also involved in various fields of petrochemical industry.

 

The combination seal that is used more under medium and high pressure conditions is a mechanical-dry gas combination seal. This type of seal is usually divided into two stages. The first stage seal is a mechanical seal, the sealing medium is a liquid, and the second stage seal

 

It is a dry gas seal, and the sealing medium is the trace medium leaked from the first-level seal and the inert gas introduced from the outside. The mechanical-dry gas combination seal is characterized by the mechanical seal as the main seal for the process medium.

 

Seal, dry gas seal is used as an auxiliary seal reinforcement seal form.

 

2. 2. 3 Controllable mechanical seal technology

 

After realizing the high parameter design and manufacture of mechanical seal, the researchers turned their research focus to the simultaneous control of leakage rate and wear. Leakage rate and wear rate are the two characteristics of mechanical seal performance.

 

parameters. The high leakage rate leads to the thickness of the liquid film between the end faces of the seal, the end face wear is small during work, and the mechanical seal has a long service life; while the low leakage rate leads to the thin liquid film between the end faces of the seal, and the end face during work

 

The wear is large and the service life of the mechanical seal is short. Therefore, it is very important to find the best working point of mechanical seal, that is, the key to realize performance control of mechanical seal.

 

In practical applications, acoustic emission technology is usually used for early seal failure monitoring, voltage or eddy current sensors are used to monitor changes in the thickness of the end face film, and resistance strain gauges are used to test torque.

 

To monitor the relationship between operating parameters and friction coefficient, the leakage monitoring method is used to monitor the sealing working condition. In addition, the mechanical seals of some key equipment even use intelligent monitoring systems.

 

system, the use of computer control technology, continuous automatic adjustment of the various parameters of the seal, in order to achieve the best operating conditions. For example, countries such as the United States and Japan will use acoustic emission, ultrasound, and microelectronics and sensing

 

The technology is applied to the mechanical seal monitoring system of the nuclear reactor condensate pump and the liquid oxygen pump in the aerospace field. The domestic petroleum university has developed the mechanical seal phase monitoring system and has been applied in industry.

 

Although controllable sealing technology is not yet widely used on a large scale at this stage, with the development of computers, electronic sensor technology and sealing theory, controllable mechanical sealing technology will be used in various fields in the future.

 

The domain is widely used.

 

3. Conclusion

 

After years of research and development, the sealing device of rotating equipment has developed from the initial simple packing seal to an advanced combination seal and controllable seal, from reducing leakage to "zero leakage", a variety of new materials.

 

New technologies are constantly improving the reliability of this device. Although seal failure events still occur in the petrochemical industry due to increasingly harsh operating conditions and operating conditions, it is believed that with the sensing

 

With the rapid development of electronics, new materials and advanced processing technology, the real environmental protection, efficient and safe sealing technology will eventually embark on the stage of history.

 

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