Petroleum and chemical industry occupy a very important position in the national economy. Chemical process pumps are also attracting more and more attention as a key supporting equipment. Due to the complex nature of the chemical medium, coupled with the continuous improvement of environmental protection requirements, how should we chemical pump selection? What should be the focus of attention and so on is particularly important. Today, Xiao Bian came to talk to you about chemical pump selection should pay attention to the matter!
Matters needing attention 1: corrosion-resistant problems
All along, corrosion is one of the most troublesome hazards of chemical equipment, a slight carelessness, ranging from damage to equipment, heavy cause accidents and even lead to disaster.
According to the statistics, about 60% of the destruction of chemical equipment is caused by corrosion. Therefore, the selection of chemical pumps should first pay attention to the scientific material selection.
There is often a misunderstanding that stainless steel is a "universal material," no matter what the media and environmental conditions are held out of stainless steel, which is very dangerous. The following for some common chemical media to talk about the selection of the main points:
1, sulfuric acid
As one of the most corrosive media, sulfuric acid is a very important industrial raw material.
Different concentrations and temperatures of sulfuric acid on the corrosion of materials vary greatly, for the concentration of more than 80%, the temperature is less than 80 ℃ of concentrated sulfuric acid, carbon steel and cast iron has good corrosion resistance, but it is not suitable for high-speed flow of sulfuric acid, Not suitable for pump valve material; common stainless steel such as 304 (0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti) sulfuric acid medium is also limited use.
Therefore, the delivery of sulfuric acid pump valve is usually made of high silicon cast iron (casting and processing difficult), high alloy stainless steel (No. 20 alloy) manufacturing, but its processing is difficult and expensive, so people are not optimistic.
Fluoroplastics alloy has good resistance to sulfuric acid. It is a patented material of Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. It has been proved by the Chinese Academy of Sciences that there is no chemical medium to react with it at present. Therefore, Fluorine fluoride pump (F46) A more economical choice.
2, hydrochloric acid
Most metal materials are resistant to hydrochloric acid corrosion (including a variety of stainless steel materials), molybdenum high ferrosilicon can only be used for 50 ℃, 30% hydrochloric acid.
In contrast to metallic materials, the vast majority of non-metallic materials have good corrosion resistance to hydrochloric acid, so lined rubber pumps and plastic pumps (such as engineering plastics, fluoroplastics, etc.) are the best choice for the delivery of hydrochloric acid.
3, nitric acid
Most metals are rapidly corroded in nitric acid. Stainless steel is the most widely used nitric acid resistant material and has good corrosion resistance to nitric acid at all concentrations. It is worth mentioning that stainless steel containing molybdenum (such as 316,316 L ) The corrosion resistance of nitric acid is not only not superior to ordinary stainless steel (such as 304,321), sometimes even worse. For high temperature nitric acid, usually using fluorine plastic alloy material.
4, acetic acid
It is one of the most corrosive substances in organic acids. Ordinary steel will be severely corroded in all concentrations and temperatures of acetic acid. Stainless steel is an excellent acid-resistant material. Molybdenum-containing 316 stainless steel is also suitable for high temperature and dilute acetic acid vapor .
For high temperature and high concentration of acetic acid or other corrosive media containing harsh requirements, the choice of high-alloy stainless steel or fluorine plastic pump. Such as CQB magnetic pump, CQ stainless steel magnetic pump.
5, alkali (sodium hydroxide)
General corrosive is not very strong, but the general alkaline solution will have a crystal, so the optional configuration of graphite 169 material mechanical seal FSB-type fluoride alloy alkali pump.
6, ammonia (ammonia hydroxide)
Most metals and non-metals in liquid ammonia and ammonia (ammonia hydroxide) in the corrosion are minor, only copper and copper alloy should not be used. At this time use CQF plastic magnetic pump, FSB fluorine alloy centrifugal pump is better.
7, salt water (sea water)
Ordinary steel in sodium chloride solution and seawater, salt water corrosion rate is not too high, generally need to use paint protection; various types of stainless steel also have a low uniform corrosion rate, but may cause localized corrosion due to chloride ions, usually 316 stainless steel better.
8, alcohols, ketones, esters, ethers
Common alcohol mediums are methanol, ethanol, ethylene glycol, propanol and so on. Ketones have acetone, butanone, etc. There are various kinds of methyl esters and ethyl esters in ester media. The ether media are methyl ether, ethyl ether, Butyl ether, etc., their basic corrosive is not strong, so you can use ordinary stainless steel, the specific selection should be based on the media properties and related requirements to make a reasonable choice.
It is also noteworthy that ketones, esters, ethers are soluble in a wide variety of rubbers and avoid mistakes when selecting sealing materials. It is recommended to choose inorganic seal fluorine plastic magnetic pump.
There are many other media can not be introduced in this one, in short, should not be arbitrarily and blindly selected materials, should consult more information or learn from mature experience.
Matters needing attention II: Chemical pump sealing problem
No leakage is the eternal pursuit of chemical equipment, it is this requirement has led to the growing use of magnetic pumps.
However, there is still a long way to go without leakage, such as the life span of the magnetic pump isolation sleeve, the material pitting problem, the reliability of the static seal, and the like.
Now some of the basic aspects of sealing a brief introduction is as follows:
1, sealed form
For the static seal, usually only two forms of seals and seals, and O-ring seal again the most widely used.
For the dynamic seal, the chemical pump seldom used packing seal, the main mechanical seal, mechanical seal and single-sided and double-ended, balanced and unbalanced type, balanced type for high pressure medium seal (usually refers to the pressure greater than 1.0MPa), double-end machine sealing is mainly used for high temperature, easy crystallization, viscosity, containing particles and toxic volatile medium, double seal should be injected into the sealed chamber isolation liquid, the pressure is generally higher than the medium pressure 0.07 ~ 0.1 MPa.
2, sealing material
Chemical magnetic pump static sealing materials generally use fluoroelastomers, special circumstances before the use of PTFE material; mechanical seal ring static material configuration is more critical, not the best cemented carbide on the high price is on the one hand, Neither hardness difference is not reasonable, so it is best to distinguish between media characteristics.
Note three: viscosity problems
The viscosity of the medium has a large effect on the performance of the pump. As the viscosity increases, the lift of the pump decreases, the head and flow of the optimum condition decrease, and the power rises accordingly, reducing the efficiency.
General parameters on the sample are the performance of the transport of water, when the transport of viscous media should be converted (different viscosity correction factor can be found in the relevant conversion chart).
For the viscosity of the pulp, paste and viscous liquid delivery, the proposed selection of mortar pump.
Pump selection principle
When installing the equipment, determine the pump's purpose and performance parameters and select the pump type. First of all, this choice from the choice of pump type and form of the beginning, then what principle to choose the pump? What is the basis?
1, Make the type and performance of the selected pump meet the requirements of process parameters such as device flow, head, pressure, temperature, NPSH, suction and so on.
2, must meet the characteristics of the media requirements
Pumps that deliver flammable, explosive toxic or valuable media require dependable shaft seals or leak-free pumps such as magnetically-driven pumps (no shaft seal, indirect magnetically isolated drive);
For conveying corrosive media pumps, convection parts require corrosion-resistant materials, such as fluorine plastic corrosion-resistant pump;
Pumps containing solid particulate media are required to have a wear-resistant material for the convection components and flush with a cleaning fluid if necessary.
3, the mechanical requirements of high reliability, low noise, small vibration.
4, the correct calculation of pump purchase cost of investment.
5, conveying corrosive media (such as "concentrated sulfuric acid, concentrated nitric acid"), the transport of flammable and explosive media, the use of the environment can not have any pollution: the choice of magnetic pump, such as "CQB series of magnetic pump, IMD series of magnetic Pump, self-priming, optional FZB fluorine plastic self-priming pump.
6, IHF centrifugal pump and FSB centrifugal pump with high speed, small size, light weight, high efficiency, large flow, simple structure, infusion without pulsation, stable performance, easy operation and maintenance features such as the use of conditions no special requirements When the centrifugal pump can be used better.
7, conveying the pump containing solid particles of chemical medium, convection parts require wear-resistant materials: UHB mortar pump for the best selection of objects, UHB corrosion-resistant wear-resistant mortar pump material for high strength new engineering plastics UHBWPE, it is a change Sexual ultra-high molecular weight (5 million or more) polyethylene. In plastic, it has excellent abrasion resistance, the experimental comparison, its wear resistance is much higher than stainless steel, and impact resistance, creep resistance and excellent corrosion resistance (with F4), as well as Adhesion and other unique properties.
8, when the liquid level below the pump installation position: FZB fluorine plastic self-priming pump should be used, such as the need to meet the characteristics of the magnetic pump, optional ZMD fluorine plastic self-priming magnetic pump
9, According to the pump performance curve to choose the best specifications Model: When the requirements of the performance parameters can not find the appropriate type of model can refer to the pump performance curve to select the most suitable pump.
Chemical pump
How to choose these types of pump?
1, the delivery of acidic water containing solid particles, the choice of what pump?
Q: We need to transport the medium a little corrosive (acidic water), which contains about 20% of the solid particles, would like to choose a corrosion-resistant wear-resistant pump?
A: If the corrosiveness is not very strong, you can choose UHB-ZK series corrosion-resistant mortar pump, the internal flow components are all made of ultra-high molecular weight polyethylene with good corrosion resistance and wear resistance can be made to transport solids Not more than 40%, corrosive medium, and long service life, easy maintenance.
If corrosive, you should choose fluorine plastic centrifugal pump, corrosion-resistant wear-resistant type of mechanical seal.
2, our medium temperature is high, highly corrosive, what pump is good?
Q: We need to transport the medium temperature is very high (about 140 degrees), corrosive (glacial acetic acid), we would like to use a leak-free, corrosion-resistant pump, what pump should I choose?
A: It is recommended to use IMD high-temperature fluorine plastic magnetic pump, the specific material is: pump casing selection Fluoroplastics alloy (F4 / F46), impeller, isolation sleeve and other components use PFA (soluble Teflon) , And good corrosion resistance.
3, conveying medium corrosive, the choice of what pump?
Q: We need to transport the media as aqua regia, at room temperature, the election what pump?
A: It is recommended to use fluorine plastic pump, fluorine plastic is one of the best corrosion-resistant materials today.
4, conveying a little corrosive media, the election what pump?
Q: We need to transport the medium concentration of 30% hydrofluoric acid, the temperature is about 40 degrees, the election what pump?
A: The choice of engineering plastics (reinforced polypropylene) pump, plastic pump can convey the range of media are as follows:
If the delivered media is found available in the table above, the following list of engineering plastic pumps is listed below:
1, CQF-type engineering plastic magnetic pump
2, FUH plastic centrifugal pump
3, QBY plastic pneumatic diaphragm pump
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