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Chemical pump

Energy saving pump jointly designed by the whole country

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Chemical pump is an energy-saving pump jointly designed by the whole country. Its performance and technical requirements are designed according to the performance and size specified in the international standard ISO2858. Its advantages: the whole series of water conservancy performance layout is reasonable, the user's selection range is wide, the "back opening" structure is convenient for maintenance, efficiency and suction head reach the international advanced level.

Chinese name: Chemical pump
Foreign name: Chemical pump

Pinyin: huà gōng bèng
Material: Fluoroplastic alloy, cast iron
Industry: Machinery manufacturing

catalog

brief introduction

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Chemical pump is an energy-saving pump jointly designed by the whole country. Its performance and technical requirements are designed according to the performance and size specified in the international standard ISO2858, which can be divided into Stainless steel chemical pump , plastic chemical pump, Fluoroplastics chemical pump , electric chemical pump, pneumatic chemical pump^[1] 。

advantage

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The advantages of chemical pumps are reasonable layout of the whole series of hydraulic performance, wide selection range of users, "back opening" structure, convenient maintenance, efficiency and suction head reaching the international advanced level.

purpose

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It is widely used for industrial and urban water supply and drainage, as well as farmland and orchard irrigation and drainage, to transport clean water or other liquids with physical and chemical properties similar to clean water.

classification

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According to the different materials of chemical pumps, their application fields are classified as follows:

1) Chemical pump（ Stainless steel material ）It is widely used in petroleum, chemical industry, metallurgy, synthetic fiber, pharmacy, food, synthetic fiber and other sectors to transport alkali Corrosive medium ；

2) Chemical pump（ Fluoroplastics Material) is used to transport any acidic and alkaline corrosive medium;

3) Chemical pumps (made of cast iron) are used for industrial and urban water supply and drainage, as well as farmland and orchard irrigation and drainage, to transport clean water or other liquids with physical and chemical properties similar to clean water.

2、 According to the different uses of chemical pumps, their classifications are introduced in detail:

1) Process pumps: including feed pump, reflux pump, circulating pump, flushing pump, sewage pump, make-up pump, output pump, etc.

2) Utility pump: including boiler pump, cooling tower pump, fire pump, water source deep well pump, etc.

3) Auxiliary pumps: including lubricating oil pump, seal oil pump, hydraulic transmission pump, etc.

4) Pipeline delivery pump: pump for oil transmission pipeline, pump for loading and unloading vehicle, etc.

3、 Classification according to working principle and structure:

1) Vane pump: When the pump shaft rotates, it drives various impeller blades to apply centrifugal force or axial force to the liquid, and transports the liquid to the pipeline or container, such as centrifugal pump, vortex pump, mixed flow pump and axial flow pump.

2) Positive displacement pump: a pump that uses the continuous change of the volume in the pump cylinder to deliver liquid, such as reciprocating pump, piston pump, gear pump, screw pump.

3) Other types of pumps: there are electromagnetic pumps that use electromagnetism to transport liquid conductive bodies; Pumps that use fluid energy to deliver liquids, such as jet pumps, air lift devices, etc.

4、 Classification by conveying medium:

1) Water pump: including clean water pump, boiler feed pump, condensate pump and hot water pump.

2) Corrosion resistant pump: including stainless steel pump, high silicon cast iron pump, ceramic acid resistant pump, impermeable graphite pump, hard rubber lined pump, rigid polyvinyl chloride pump, canned motor pump, diaphragm pump, titanium pump, etc.

3) Impurity pump: including slurry pump, sand pump, sewage pump, coal powder pump, ash pump, etc.

4) Oil pump: cold oil pump, hot oil pump, submersible pump, slurry pump, liquid hydrocarbon pump, etc.

5、 Classification according to service conditions:

1) Large flow and micro flow pumps: the flow is 300m ³/min and 0. O1L/min respectively;

2) High temperature pump and low temperature pump: high temperature up to 500 ℃, low temperature down to - Z53 ℃;

3) High pressure pump and low pressure pump: high pressure up to 200MPa, vacuum degree 2.66 -- 10.66kPa (20-80mmHg);

4) High speed pump and low speed pump: high speed up to 24000r/min, low speed 5-10r/min;

5) Accurate metering pump: the metering accuracy of flow is ± 0 3%；

6) High viscosity pump: viscosity up to several kilopascals (Pa · s)^[1] 。

working principle

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Negative pressure pump

Before starting the pump, Suction pipe And the pump must be filled with liquid. After the pump is started, the impeller rotates at a high speed. The liquid in the impeller rotates with the blade. Under the centrifugal force, it flies away from the impeller and shoots out. The speed of the injected liquid in the diffusion chamber of the pump housing gradually slows down, the pressure gradually increases, and then flows out from the pump outlet and discharge pipe. At this time, due to the liquid being thrown around at the center of the blade, a vacuum low-pressure area with neither air nor liquid is formed. Under the effect of the atmospheric pressure on the pool surface, the liquid in the liquid pool flows into the pump through the suction pipe. In this way, the liquid is continuously pumped up from the liquid pool and continuously flows out of the discharge pipe.

Positive pressure pump

It mainly refers to the working principle of the submerged pump. Taking the submerged pump and the long shaft submerged pump in the gas station as an example, the submerged pump submerges the motor and the pump together into the tank bottom, and the motor drives the impeller to boost the pressure to push the medium to the ground target. The long shaft submerged pump connects the pump and the motor separately with a long shaft, and its working principle is to transport the medium under positive pressure, Therefore, the problem of air resistance and cavitation of impeller caused by negative pressure conveying medium is solved. The motor of the submersible pump is not above the liquid level, but below the liquid level. The motor is a submersible motor, which is connected with the pump wheel into a potential liquid. The main advantages of this design are: the pump bearing is only a few hundred millimeters, there is no long shaft, there is no swing problem, the operation is stable, the sound is very low, and there is almost no wear.

Sealing form of chemical pump

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It mainly includes oil seal, gasket seal, thread seal, labyrinth seal, packing seal, power seal and mechanical seal.

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Oil seal

It is a self tightening lip seal with simple structure, small size, low cost, convenient maintenance and small resistance torque. It can not only prevent medium leakage, but also prevent the invasion of external dust and other harmful substances. It also has a certain compensation ability for wear, but it is not resistant to high pressure, so it is generally used in chemical pumps in low-pressure occasions.

2、 Gasket seal

Gasket is the basic element of static seal of centrifugal pump, and its application range is very wide. The selection of gaskets is mainly determined by factors such as the medium conveyed by the chemical pump, temperature, pressure and corrosivity.

3、 Thread seal

Generally, there are two types of chemical pumps, one is the threaded connection gasket seal, the other is the threaded and filled seal, both of which are used in the sealing of small diameter threaded connections. The sealing element of the gasket seal of the threaded electric diaphragm pump is the gasket, and the thread only serves to provide the compression force.

4、 Labyrinth seal

When the design is reasonable, the processing is excellent, the assembly is complete, and the speed is high, the labyrinth seal effect is good. However, in practical applications, the resulting chemical pump leakage is very large, so it is not commonly used in chemical pump seals.

5、 Packing seal

The packing with compressibility and resilience is put into the stuffing box, and the axial compression force of the gland is converted into the radial sealing force to play a sealing role.

This sealing method is called packing sealing, and this packing is called sealing packing. The packing seal is widely used in the design of chemical pumps because of its simple structure, convenient replacement, low price, wide adaptability to speed, pressure and medium.

6、 Power seal

When the chemical pump is running with, the pressure head generated by the auxiliary impeller balances the high-pressure liquid at the outlet of the main impeller, thus achieving sealing. The auxiliary impeller does not work during shutdown, so the shutdown sealing device must be equipped at the same time to solve the possible leakage of chemical pump during shutdown.

The auxiliary impeller seal is simple in structure, reliable in sealing and long in service life. The chemical pump can achieve no leakage during operation, so it is often used in the chemical pump to transport media containing impurities.

7、 Mechanical seal

Chemical pump industry is the most widely used seal form. Because mechanical seal has the advantages of less leakage and long life, mechanical seal is the most important shaft seal form in these equipment in the world today. Mechanical seal, also called end face seal, is defined in the relevant national standards as "a device to prevent fluid leakage, which is composed of at least one pair of end faces perpendicular to the rotation axis, under the action of fluid pressure, elastic force (or magnetic force) of compensation mechanism, and the cooperation of auxiliary seal, to keep sticking and relative sliding."^[1]

technical parameter

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For a long time, corrosion is one of the most troublesome hazards of chemical equipment. A little carelessness may damage equipment, or even cause accidents or even disasters. According to relevant statistics, about 60% of the damage of chemical equipment is caused by corrosion. Therefore, when selecting chemical pumps, we should first pay attention to the scientificity of material selection. There is usually a misunderstanding that stainless steel is a "universal material". It is very dangerous to hold stainless steel pumps regardless of media and environmental conditions. Here are the key points of material selection for some common chemical media:

1. As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of uses. The corrosion of sulfuric acid with different concentrations and temperatures on materials varies greatly. For concentrated sulfuric acid with concentration above 80% and temperature below 80 ℃, carbon steel and cast iron have good corrosion resistance, but they are not suitable for high-speed sulfuric acid and are not suitable for pump valve materials; Ordinary stainless steel, such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti), also has limited use for sulfuric acid medium. Therefore, the pump valve for sulfuric acid delivery is usually made of high silicon cast iron (difficult to cast and process) and high alloy stainless steel (No. 20 alloy). Fluoroplastics have good sulfuric acid resistance, so it is a more economical choice to use fluorine lined pumps (F46).

2. Most metal materials in hydrochloric acid are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and molybdenum containing high silicon iron can only be used for hydrochloric acid below 50 ℃ and 30%. Contrary to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so rubber lined pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choice for delivering hydrochloric acid.

3. Most common metals in nitric acid are rapidly corroded and destroyed in nitric acid. Stainless steel is the most widely used nitric acid resistant material, which has good corrosion resistance to all concentrations of nitric acid at room temperature. It is worth mentioning that the corrosion resistance of molybdenum containing stainless steel (such as 316, 316L) to nitric acid is not only not better than ordinary stainless steel (such as 304, 321), but sometimes even worse. For high-temperature nitric acid, titanium and titanium alloy materials are usually used.

4. Acetic acid is one of the most corrosive substances in organic acids. Ordinary steel will be severely corroded in acetic acid of all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material. Molybdenum containing 316 stainless steel can also be used for high temperature and dilute acetic acid steam. High alloy stainless steel pump or fluoroplastic pump can be selected for high temperature and high concentration acetic acid or other corrosive media.

5. Alkali (sodium hydroxide) steel is widely used in sodium hydroxide solution below 80 ℃ and within 30% concentration. Many factories still use ordinary steel at 100 ℃ and below 75%. Although corrosion increases, it is economical. The corrosion resistance of ordinary stainless steel to alkali solution has no obvious advantages compared with cast iron. As long as a small amount of iron is allowed to be mixed in the medium, stainless steel is not recommended. For high-temperature alkaline solution, titanium and titanium alloy or high alloy stainless steel are mostly used.

6. Ammonia (ammonia hydroxide) Most metals and nonmetals are slightly corroded in liquid ammonia and ammonia water (ammonia hydroxide), and only copper and copper alloys are not suitable for use.

7. The corrosion rate of salt water (sea water) ordinary steel in sodium chloride solution, sea water and salt water is not too high, and it must be protected by coating generally; All kinds of stainless steel also have low uniform corrosion rate, but may cause local corrosion due to chloride ion. Generally, 316 stainless steel is preferred.

8. Common alcohol media of alcohols, ketones, esters and ethers include methanol, ethanol, ethylene glycol, propanol, etc. Ketone media include acetone, butanone, etc. Ester media include various methyl esters, ethyl esters, etc. Ether media include methyl ether, ether, butyl ether, etc., which are basically non corrosive, and common materials are applicable, The specific selection should also be based on the properties of the media and related requirements to make a reasonable choice. In addition, it is worth noting that ketones, esters and ethers are soluble to a variety of rubbers, so mistakes should be avoided when selecting sealing materials.

Cooling problems

The transportation of high-temperature medium puts forward higher requirements for the structure, materials and auxiliary system of the pump. Now let's talk about the cooling requirements of different temperature changes and the pump types applicable to the company:

1. For the medium whose temperature is lower than 120 ℃, there is usually no special cooling system, and its own medium is mostly used for lubrication and cooling. For example, IHG, ISWH chemical pump, PHG shielded chemical pump (when the temperature exceeds 90 ℃, the protection level of shielded motor shall be H); The upper temperature limit of CZ ordinary type and IH chemical pump can reach 140 ℃~160 ℃ due to the suspension structure; The maximum operating temperature of the IHF fluorine lined pump can reach 200 ℃; Only CQB ordinary magnetic pump is used at a temperature not exceeding 100 ℃. It is worth mentioning that the media that are easy to crystallize or contain particles should be equipped with sealing surface flushing pipelines (interfaces are reserved during design).

2. For the medium above 120 ℃ and within 300 ℃, generally, a cooling chamber must be set on the pump cover, and the sealing chamber should also be connected with coolant (it must be equipped with a double end mechanical seal). When the coolant is not allowed to penetrate into the medium, its own medium should be connected after cooling (it can be achieved through a simple heat exchanger). In addition, CQB-G high-temperature magnetic pump can be used for high-temperature medium within 280 ℃.

3. For high temperature medium above 300 ℃, not only the pump head needs to be cooled, but also the suspension bearing chamber should be equipped with a cooling system. The pump structure is generally in the form of central support. The mechanical seal should preferably be of metal bellows type, but the price is high (more than 10 times the price of ordinary mechanical seal).

Sealing problems

Leakage free is the eternal pursuit of chemical equipment. It is this requirement that has led to the growing application of magnetic pump and canned motor pump. However, there is still a long way to go to truly achieve no leakage, such as the life of magnetic pump isolation sleeve and canned motor pump shielding sleeve, material pitting, reliability of static seal, etc. Some basic information about sealing is briefly introduced as follows:

1. For static seal, there are usually only two types of seal gasket and seal ring, and O-ring is the most widely used seal ring; For dynamic seals, chemical pumps rarely use packing seals, which are mainly mechanical seals. Mechanical seals can be divided into single end and double end, balanced type and unbalanced type. The balanced type is suitable for sealing high-pressure media (usually the pressure is greater than 1.0MPa). Double end mechanical seals are mainly used for media with high temperature, easy crystallization, viscosity, particles and toxic volatilization, The double end mechanical seal shall be injected with isolating liquid into the seal chamber, whose pressure is generally 0.07~0.1MPa higher than the medium pressure.

2. Sealing material The static sealing material of chemical pump is generally fluororubber, and polytetrafluoro material is only used in special circumstances; The material configuration of the dynamic and static rings of mechanical seals is more critical, and hard alloy is not the best for hard alloy. On the one hand, the price is high, and there is no difference in hardness between the two is not reasonable, so it is best to treat them differently according to the characteristics of the media.

(Note: The typical configuration of mechanical seal and pipeline system in the 8th edition of API 610 of American Petroleum Institute is detailed in Appendix D)

Viscosity problem

The viscosity of the medium has a great impact on the performance of the pump. When the viscosity increases, the head curve of the pump decreases, and the head and flow under the optimal working condition decrease, while the power increases, thus reducing the efficiency. Generally, the parameters on the sample are the performance when conveying clean water. When conveying viscous media, conversion should be carried out (for correction factors of different viscosities, refer to the relevant conversion chart). For the transportation of slurry, paste and viscous liquid with high viscosity, it is recommended to use screw pump. The viscosity of G single screw pump can reach 1000000cst.

matters needing attention

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Extended service life

In order to make the pump run normally, we should form a good habit of inspection and maintenance every day, which can avoid many troubles and also improve the work efficiency. Therefore, daily inspection and maintenance are very important and should not be ignored.

environmental quality

Although the operating environment of pumps in our country is constantly improving, there are still some people who put pumps in places with poor environment. However, if they are placed in places with poor conditions, they should always clean them. In this case, people should always check and maintain them.

Daily inspection

In the daily inspection, we should not only fully control the operation of chemical pumps and test the instruments, but also give play to people's subjective initiative. Check whether the pressure, current, voltage, flow and temperature indicated by various instruments are normal, whether there is deformation, deformation, leakage, blockage, etc; Listen to whether there is any abnormal sound in each part, such as impact sound, breaking sound, friction sound, etc. At the same time, pay attention to whether the vibration of the chemical pump is very large.

Number of inspections

In order to ensure the working efficiency when using chemical pumps, everyone should check at least twice a day, even if Degree of automation Regular inspection is also required for higher pumps.

development

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Driven by the huge demand for oil, the middle east and coastal areas of China have become the fastest growing regional market for the pump valve industry. As China's investment in environmental water treatment, coal chemical industry, urban infrastructure and other related fields is further increased, the pump valve industry will also benefit again. According to the analysis of experts in the industry, the demand for pump valves in the domestic market will continue to grow by more than 10% in the next few years, and will increase year by year.

Pump valve The ratio in the domestic market is rising, and the import and export are also showing no weakness. According to the statistical survey of Zhejiang Pump and Valve Industry Association, it is estimated that by 2020, China's import of pump and valve equipment will reach a staggering $80 billion, surpassing the US $70 billion and becoming the world's largest pump and valve importer. At that time, Japan, India, Germany and France will rank third to sixth in the import volume of pump and valve equipment.

If China's pump valve industry wants to have long-term development, it must adjust and optimize the industrial structure. It must not only continue to give full play to the advantages of the traditional pump valve industry, but also vigorously develop knowledge and technology intensive industries and emerging industries to promote the upgrading of the valve industry. Only in this way can the gap between China's valve industry and developed countries be shortened as soon as possible. Therefore, as long as enterprises can seize the opportunity, strengthen research and development capabilities, and constantly improve the scientific and technological content and product quality of products, they will be able to take the initiative in the broad market competition^[1] 。

Material selection method

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2. Most metal materials of hydrochloric acid are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and molybdenum containing high silicon iron can only be used for hydrochloric acid below 50 ℃ and 30%. Contrary to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so rubber lined pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choice for delivering hydrochloric acid.

3. Most common metals in nitric acid are rapidly corroded and destroyed in nitric acid. Stainless steel is the most widely used nitric acid resistant material, which has good corrosion resistance to all concentrations of nitric acid at room temperature. It is worth mentioning that stainless steel containing molybdenum (such as 316, 316L) is not only inferior to ordinary stainless steel (such as 304, 321), but sometimes even inferior to nitric acid. For high-temperature nitric acid, titanium and titanium alloy materials are usually used.

6. Ammonia (ammonia hydroxide) Most metals and nonmetals are slightly corroded in liquid ammonia and ammonia water (ammonia hydroxide), and only copper and copper alloys are not suitable for use.

8. Common alcohol media of alcohols, ketones, esters and ethers include methanol, ethanol, ethylene glycol and propanol; ketone media include acetone and butanone; ester media include various methyl esters and ethyl esters; ether media include methyl ether, ether and butyl ether, which are basically non corrosive and can be applied to commonly used materials, The specific selection should also be based on the properties of the media and related requirements to make a reasonable choice. In addition, it is worth noting that ketones, esters and ethers are soluble to a variety of rubbers, so mistakes should be avoided when selecting sealing materials.

There are many other media that cannot be introduced here one by one. In short, we must not be arbitrary and blind when selecting materials. We should consult more relevant materials or learn from mature experience^[1] 。

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