Chemical pump, the right choice is the pump, the wrong choice is the accident chemical pump valve and pipeline equipment antifreeze measures

Chemical pump, the right choice is the pump, the wrong choice is the accident chemical pump valve and pipeline equipment antifreeze measures

The petroleum and chemical industry occupy a very important position in the national economy, and the chemical process pump as a key supporting equipment has been paid more and more attention. Because of the complex characteristics of the chemical medium, coupled with the increasing requirements of environmental protection, how should we choose the type of chemical pump? What should be paid attention to and so on are particularly important. Xiaobian to talk with you about the chemical pump selection should pay attention to matters!
Note one: corrosion resistance
Corrosion has always been one of the hazards of chemical equipment. If you are careless, the equipment will be damaged, and the heavy will cause accidents or even disasters.
According to relevant statistics, about 60% of the damage of chemical equipment is caused by corrosion, so we should first pay attention to the scientific nature of material selection when selecting chemical pump.
There is usually a misunderstanding that stainless steel is “material”, no matter what medium and environmental conditions are holding out stainless steel, this is very dangerous. The following for some common chemical medium to talk about the main points of material selection:
1, sulfuric acid,
As one of the strong corrosive media, sulfuric acid is a very versatile and important industrial raw material.
Different concentrations and temperatures of sulfuric acid on material corrosion difference is large, for the concentration of more than 80%, the temperature is less than 80℃ concentrated sulfuric acid, carbon steel and cast iron have better corrosion resistance, but it is not suitable for high-speed flow of sulfuric acid, not suitable for the pump valve material; Ordinary stainless steel such as 304(0Cr18Ni9), 316(0Cr18Ni12Mo2Ti) also has limited use for sulfuric acid medium.
Therefore, the pump valve for conveying sulfuric acid is usually made of high-silicon cast iron (casting and processing difficulty), high-alloy stainless steel (No. 20 alloy), but its processing difficulty and expensive, so it is not favored by people.
Fluorine plastic alloy has a very good sulfuric acid resistance, it is the Chinese Academy of Sciences Shanghai Institute of Organic Chemistry patent material, the Chinese Academy of Sciences experiment proved that there is no chemical medium can react with it, so the use of fluorine lined pump (F46) is a more economic choice.
2, hydrochloric acid
Most metal materials are not resistant to hydrochloric acid corrosion (including a variety of stainless steel materials), molybdenum-containing ferrosilicon can also be used for 50℃, 30% below hydrochloric acid.
In contrast to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so lined rubber pump and plastic pump (such as engineering plastics, fluorine plastics, etc.) is a better choice to transport hydrochloric acid.
3, nitric acid
General metals are mostly rapidly corroded in nitric acid, stainless steel is widely used in nitric acid resistance materials, all concentrations of nitric acid at room temperature have good corrosion resistance, it is worth mentioning that molybdenum containing stainless steel (such as 316, 316L) corrosion resistance to nitric acid is not better than ordinary stainless steel (such as 304, 321), sometimes even worse. For high temperature nitric acid, fluorine plastic alloy material is usually used.
4, acetic acid,
It is one of the most corrosive substances in organic acids. Ordinary steel will be seriously corroded in acetic acid of all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material, and molybdenum 316 stainless steel can also be used for high temperature and dilute acetic acid steam.
For high temperature high concentration acetic acid or containing other corrosive medium and other harsh requirements, can choose high alloy stainless steel or fluorine plastic pump. Such as CQB magnetic pump, CQ stainless steel magnetic pump.
5. Base (sodium hydroxide)
Generally corrosive is not very strong, but the general alkali solution will produce crystallization, so you can choose the FSB type fluoroalloy alkali pump with the mechanical seal of silica graphite 169 material.
6. Ammonia (ammonia hydroxide)
The corrosion of most metals and non-metals in liquid ammonia and ammonia (ammonia hydroxide) is very mild. Only copper and copper alloys should not be used. At this time, CQF engineering 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 must use paint protection; All kinds of stainless steel also has a very low uniform corrosion rate, but may cause local corrosion due to chloride ions, usually 316 stainless steel is better.
8, alcohol, ketones, esters, ethers
Common alcohol medium such as methanol, ethanol, ethylene glycol, propylene glycol, ketone, such as medium, there are all kinds of methyl esters medium, ethyl ester, ethers media such as methyl ether, butyl ether, their basic not strong corrosive, so all can choose ordinary stainless steel, concrete selection should also according to the requirements of the dielectric properties and related make reasonable choice.
In addition, it is worth noting that ketone, ester and ether are soluble to a variety of rubber, and avoid mistakes when choosing sealing materials. It is recommended to choose inorganic sealed fluorine plastic magnetic pump.
There are many other media can not be introduced in this one by one, in short, in the selection of materials must not be random and blind, should consult more relevant information or learn from mature experience.
Note two: chemical pump seal problem
No leakage is the eternal pursuit of chemical equipment, and it is this requirement that has contributed to the increasing application of magnetic pump.
However, there is still a long way to go to achieve no leakage, such as the service life of the magnetic pump isolation sleeve, the corrosion of the material, the reliability of the static seal and so on.
Some basic information about sealing is briefly introduced as follows:
1. Sealing form
For static sealing, there are usually only two forms of gasket and sealing ring, and the sealing ring is widely used in O-ring.
For dynamic seal, chemical pump packing seal, is scarcely used to is given priority to with mechanical seal, mechanical seal and single face and double face, equilibrium and non-equilibrium model, equilibrium model is suitable for the seal of high pressure medium (usually refers to the pressure is greater than 1.0 MPa), double end face sealing machine is used for high temperature, easy to crystallization, viscosity, and toxic volatile medium including particle, The double-end machine seal should inject isolation liquid into the sealing cavity, and the pressure is generally higher than the medium pressure 0.07~0.1MPa.
2. Sealing material
Chemical magnetic pump static seal material generally uses fluorine rubber, special cases only use PTFE material; The material configuration of mechanical seal dynamic ring is more critical, not hard alloy on hard alloy is better, the price is high on the one hand, the two have no poor hardness is not reasonable, so it is better to discriminate according to the characteristics of the medium.
Note three: viscosity problem
The viscosity of the medium has a great influence on the performance of the pump. When the viscosity increases, the pump head curve drops, and the head and flow in better working conditions decline, while the power rises accordingly, so the efficiency is reduced.
Generally, the parameters on the sample are the performance of clean water transportation, and conversion should be carried out when transporting viscous media (please refer to the relevant conversion chart for the correction coefficients of different viscosity).
For the transport of higher viscosity slurry, paste and viscous liquid, it is recommended to choose mortar pump.
Pump selection principle
In the installation of equipment, to determine the use of the pump and performance parameters and select the pump type. This choice first has to start from the choice of the type and form of the pump, so in what principle to choose the pump? On what basis?
1. Make the type and performance of the selected pump meet the requirements of the device flow, head, pressure, temperature, cavitation allowance, suction and other process parameters.
2, must meet the requirements of the medium characteristics
For the transmission of inflammable, explosive, toxic or valuable medium of the pump, the shaft seal is required to be reliable or no leakage pump, such as magnetic drive pump (no shaft seal, the use of isolation magnetic indirect drive);
For the transmission of corrosive medium pump, the convection parts are required to use corrosion resistant materials, such as fluorine plastic corrosion resistant pump;
For the transmission of pumps containing solid particle medium, the convection parts are required to use wear-resistant materials, and when necessary, the shaft seal is washed with clean liquid.
3, mechanical requirements of high reliability, low noise, small vibration.
4. Correctly calculate the input cost of pump purchase.
5, transport corrosive medium (such as “concentrated sulfuric acid, concentrated nitric acid”), transport flammable and explosive medium, the use of the environment should not have any pollution: can choose magnetic pump, such as “CQB series magnetic pump, IMD series magnetic pump, if you need to self-priming, can choose FZB fluorine plastic self-priming pump.
6. IHF centrifugal pump and FSB centrifugal pump have the characteristics of high speed, small volume, light weight, high efficiency, large flow, simple structure, no pulsation in infusion, stable performance, easy operation and convenient maintenance, such as the use of conditions without special requirements, can choose the centrifugal pump is better.
7, the transmission of solid particle chemical medium pump, the convection parts are required to use wear-resistant materials: UHB mortar pump is a better choice of objects, UHB corrosion resistance wear-resistant mortar pump material for the highest degree of new engineering plastic UHBWPE, it is a modified ultra-high molecular weight (more than 5 million) polyethylene. Among plastics, it has excellent wear resistance. Experimental comparison shows that its wear resistance is much higher than that of stainless steel, and it has unique properties such as impact resistance, creep resistance and good corrosion resistance (comparable to F4), as well as non-adhesion.
8. When the medium liquid level is below the installation position of the pump: FZB fluoroplastic self-priming pump should be selected. If you also need to meet the characteristics of the magnetic pump, ZMD fluoroplastic self-priming magnetic pump can be selected
9, according to the pump performance curve to choose a better specification model: when the use requirements in the performance parameter table can not find the suitable model can refer to the pump performance curve to choose the most suitable pump type.
Chemical pump