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Kaiyan News

What are the valves in the petrochemical industry

Time: 2016-12-23

Demand of petrochemical industry for petrochemical general valves and special valves

Petrochemical industry refers to the production of gasoline, kerosene, diesel, lubricating oil, liquefied petroleum gas and other petroleum products with petroleum and natural gas as raw materials; It is a modern industry that uses light oil as raw material to produce olefins and aromatics, and then produce synthetic resin, synthetic fiber, synthetic rubber and various chemical raw materials.

There are oil refineries, ethylene plants, chemical fiber plants, chemical plants, fertilizer plants, etc. in the petrochemical industry, many large-scale joint enterprises have become integrated factories of oil refining and chemical industry.

The production unit of the refinery is divided into primary processing unit, secondary processing unit, tertiary processing unit and auxiliary production unit. The primary processing unit processes crude oil by physical straight distillation. The product obtained is called straight distillation product. The unit used is atmospheric and vacuum distillation unit. The secondary processing device is a physical-chemical process that reprocesses the products processed at one time. The purpose is to improve the yield of light hydrocarbons, improve product quality, increase oil varieties and improve the economic benefits of refineries. The units used include safety valves such as catalytic cracking, hydrofining, hydrocracking, delayed coking and lubricating oil production units.

Ethylene plant: ethylene cracking is a leading device in the production unit of petrochemical plant. Downstream devices include resin series, such as polyethylene, polypropylene, polyvinyl chloride, polystyrene and ABS; Chemical fiber series include polyester, acrylic, vinylon and nylon.

Valves: Petrochemical valves are the most equipment in petrochemical production units. All kinds of gas and liquid media in petrochemical production must pass through various valves and be blocked or transported to various containers and process equipment according to the needs of the production process. Valves commonly used in petrochemical production are divided into general valves and special valves. Petrochemical general valves include gate valves, globe valves, ball valves, check valves, butterfly valves, pressure reducing valves, safety valves, regulating valves, etc; Petrochemical special valves include slide valve and high-temperature butterfly valve in catalytic cracking unit, four-way switching valve and coke blocking valve in delayed coking unit, high-temperature cracking flat gate valve and low-temperature valve in ethylene cracking unit, solid valve in polyethylene and polypropylene unit, high-temperature and high-pressure angle stop valve and throttle valve in synthetic ammonia unit, etc.

Petrochemical General valves: the domestic valve manufacturing industry is all over the country, with 1300 general valve manufacturers, which has become one of the largest valve output and market demand in the world. However, China’s valve industry is mostly small and medium-sized enterprises, with mixed good and bad, and only a dozen with an annual output value of more than 100 million yuan. Even compared with other domestic machinery industries, there is a big gap in terms of device and technical level, and few units really have the ability to independently research and develop high-end products. The specifications and models of valve products in China have reached more than 40000, most of which have been standardized and serialized, and some can be produced in accordance with international standards. The service temperature of the valve has reached 570 ℃, the temperature is as low as – 196 ℃, the pressure is as high as 600MPa, and the diameter is as large as 5350mm. General general valves basically meet most of the needs of petrochemical production, but for special valves such as safety valves, globe valves, check valves and other products, due to less sealing materials and improper matching of sealing materials, the heat treatment process can not meet the requirements, affecting the performance and service life of the valve. Automatic valves, such as safety valves, pressure reducing valves and steam traps, lack experimental research means, and the performance of some products is unstable. Butterfly valve, throttle valve and other control valves generally have no regulation characteristic curve and resistance coefficient curve due to the lack of test means. The control level of electric actuator is low, the control is ineffective and the accuracy is not high.

The technical level of foreign general valves is high and the development speed is fast, which is mainly reflected in: the valve is developing towards large-scale, high parameter, automation and complete set, the product series is increasing, the quality level of new valve products is high, the sealing can be * and the service life is long; Valve research is specialized and has a scientific research and testing base, which can carry out a variety of tests such as thermal performance, dynamic performance, wear resistance, earthquake resistance, fire prevention and reliability, and can carry out various performance tests on products.

With the development of petrochemical industry and the requirements of technological progress, the demand for high parameter general-purpose valves increases, such as the service temperature of high-temperature valves reaches 500 ~ 900 ℃; The service temperature of low-temperature valve reaches – 40 ~ – 190 ℃; The service pressure of high-pressure valve reaches 300 ~ 500MPa; Especially for valves with inflammable, explosive, strong corrosion and * * * * medium, higher and stricter requirements are put forward for the safety, functional reliability and service life of the valve.

In terms of valve material selection and manufacturing process, we should first meet the requirements of use, improve the safety and reliability of the valve, and pay attention to economy. In recent years, there have been many new high-performance materials, such as various strongly corrosion-resistant titanium and zirconium metal materials, nano materials, organic synthetic and polymer materials, industrial ceramics and other inorganic non-metallic materials and various composite materials. At the same time, there have been many new processes and new technical equipment for molding and surface treatment, such as casting, welding, spray welding, spraying, composite and sintering, It is being applied to valve production.

In order to adapt to the development of information technology, as the terminal actuator to control the fluid movement in the pipeline, valves are applying modern computing technology, sensing technology, network and remote control technology and intelligent technology to valve products, especially regulating valves, pressure reducing valves and safety valves.

Petrochemical special valves: among the petrochemical special valves, the typical ones should be the single acting slide valve and double acting slide valve in the catalytic cracking unit. The single acting slide valve sends the carbon deposited catalyst into the regenerator for combustion, or leads the regenerated catalyst from the regenerator to the riser. The design pressure is 0.2 ~ 0.3MPa. The design temperature is 500 ~ 900 ℃. Double acting slide valve is a valve used to control the pressure of regenerator. The operating medium is high-temperature flue gas with trace catalyst. The design pressure is 0.3MPa and the design temperature is 870 ℃. The slide valve is driven by pneumatic or motor. In the pneumatic motor transmission system, the pneumatic signal of 0.2 ~ 1.0kgf/cm2 is received through the valve positioner. The control system composed of command valve, wrong air exhaust valve and quick opening valve can achieve 1 / 400 sensitivity and 1 / 100 accuracy. This slide valve is produced by only a few factories in China.

The specification of cracking gas valve and sliding coke valve of ethylene cracking unit is 3 ~ 42 inches, and the operating temperature is 415 ~ 593 ℃. Welded structure, sealing surface surfacing cemented carbide. Parallel double ram, sealing pair without friction. Disc spring group and wedge mechanism ensure the flexibility of the valve. The expansion joint in the valve can prevent the cracking gas from leaking to the valve cavity. The motor drive and valve body are made of 15CrMo, and the internals are made of 15CrMo, 35CrMo and 2Cr13. At present, part of this valve can be manufactured in China, and large-diameter valves need to be imported from abroad.

The high-temperature and high-pressure angle stop valve and throttle valve in the synthetic ammonia unit have a working temperature of 560 ℃, nominal pressure P ≤ 42MPa, nominal size dn10 ~ 110mm, and the medium is methanol, hydrogen sulfide, nitrogen, etc. There are also oxygen stop valves and ball valves in the air separation unit, with nominal size DN ≤ 900mm, low temperature – 196 ℃, nominal pressure 0.2 ~ 16MPa. In addition, there are special valves for wellhead devices commonly used in oil exploitation, such as oil import valves with nominal pressure of api2000 ~ 20000psi; Api6a flat gate valve, angle throttle valve and pilot safety valve for natural gas wellhead; API6D all welded ball valve and metal seal ball valve with pressure change for long-distance oil and gas pipeline.

These Petrochemical special valves are difficult to manufacture, complex technology and high quality and reliability requirements. They must be properly selected and strict manufacturing process, which can not be achieved by general valve manufacturers. However, these valves are commonly used in petrochemical production, with high technical content and high value.

Because petrochemical production is basically in high temperature, high pressure, flammable, explosive, corrosive and * * * * media, if the valve is not opened and closed properly or sealed tightly, leakage will occur, resulting in fire, explosion and other serious personal and property accidents. Therefore, although the Petrochemical valve technology is not very complex, it has high quality requirements. In the history of domestic petrochemical production, fire accidents caused by high-temperature valve leakage of oil refining unit occur from time to time, dozens of casualties caused by hydrogen valve leakage and explosion of oxygenation unit, and suffocation and death of maintenance workers caused by nitrogen valve leakage occur almost every year.

At present, China’s valve industry is very complex and competitive. Most valve factories pursue technological progress and work hard to improve quality. There are also some valve factories with lax management, ignoring quality, and even using Jerry built materials to reduce costs, such as reducing the wall thickness of the valve body, selecting unqualified materials, and even counterfeiting brands. Some brand valve factories infinitely expanded the scope of joint venture, but lost their management. The valve quality decreased significantly and smashed their own brand. In recent years, fake and shoddy valves have been found repeatedly in petrochemical transformation and expansion projects, which is very dangerous.

The annual purchase of valves in the national petrochemical industry can reach 2.2 billion yuan. Common valves can be based at home, and high-temperature, high-pressure, low-temperature, corrosion-resistant and solid valves may also be imported from abroad.

The petrochemical industry is basically under the conditions of high temperature, high pressure, flammability, explosion, corrosion, * * * * and continuous production. The production cycle now requires 2 ~ 3 years to stop for major maintenance. There are 200 ~ 300 sets of equipment in one unit, and more than a dozen sets of units and 3000 ~ 4000 sets of equipment in one petrochemical plant. If one equipment goes wrong, the whole unit shall be shut down; If a set of devices cannot resume production soon, the whole plant will stop production, and the daily economic loss will reach tens of millions of yuan. If a fire explosion accident is caused, it will cause heavy losses to human life and property. Therefore, the petrochemical industry has strict requirements for technicians and reliability of equipment. For manufacturers, we must pay special attention to product quality on the premise of ensuring service performance. We must not allow rough manufacturing, fraud, shoddy goods and bad goods instead of good ones.

Therefore, Sinopec, PetroChina and CNOOC have established their own equipment procurement network: Sinopec material resources market, first-class supply network of CNPC and qualified suppliers of CNOOC. When entering this procurement network, enterprises are required to apply and provide enterprise manufacturing capacity data, manufacturing qualification certificate and product identification certificate, Only after sending personnel to the factory for investigation and strict approval procedures can they enter the procurement network and issue a network access certificate. Only manufacturing enterprises with certificates are eligible to participate in bidding and procurement. The qualification is reviewed once a year, and manufacturing enterprises with major problems will be eliminated.

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