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How to choose chemical process pump in complex chemical medium
Petrochemical industry in the national economy occupy a very important position, chemical process pump as a key ancillary equipment is also more and more people's attention. Due to the complex nature of chemical media, combined with the continuous improvement of user requirements, as a manufacturer, how should we choose? Should pay attention to what aspects? ... And so on is particularly important. Now combined with the company's related product features and personal understanding of the common sense of the selection of chemical pumps to make a brief comment, hoping to benefit my colleagues in this field to better work. Corrosion resistance has been the corrosion of chemical equipment is one of the most headache hazards, a slight carelessness, ranging from damage to equipment, heavy cause accidents 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 a strong corrosive medium, sulfuric acid is a very broad use of important industrial raw materials. 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 usually adopts high silicon cast iron (casting and processing difficult), high alloy stainless steel (20 alloy) manufacturing. Fluoroplastic has good resistance to sulfuric acid, the use of fluorine pump (F46) is a more economical choice. Company products are: IHF lining pump, PF (FS) strong corrosion-resistant centrifugal pumps, CQB-F Fluorine plastic magnetic pump. 2. Hydrochloric acid solution Most of the metal materials are not resistant to hydrochloric acid corrosion (including a variety of stainless steel), 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 polypropylene, fluoroplastic, etc.) is the best choice for the delivery of hydrochloric acid. Company products are: IHF lining fluoride pump, PF (FS) strong anti-corrosion centrifugal pump, CQ polypropylene magnetic pump (or fluorine plastic magnetic pump). 3. Nitric acid Most metals are mostly corrosive in nitric acid corrosion damage, stainless steel is the most widely used nitric acid-resistant materials, all concentrations of nitric acid at room temperature have good corrosion resistance, it is worth mentioning that the molybdenum-containing stainless steel (such as 316,316 L) corrosion resistance to nitric acid is not only not superior to ordinary stainless steel (such as 304,321), and sometimes even worse. For high temperature nitric acid, usually titanium and titanium alloy materials. The company applies products: DFL (W) H chemical pump, DFL (W) PH shield chemical pump, DFCZ process pump, DFLZP self-absorption chemical pump, IH chemical pump, CQB magnetic pump, 4. Acetic acid It is one of the most corrosive substances in organic acids. Ordinary steel will be seriously corroded in all concentrations and temperatures of acetic acid. Stainless steel is an excellent acetic acid-resistant material. Molybdenum-containing 316 stainless steel is also suitable for high temperature and Dilute acetic acid steam. 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. 5. Alkali (sodium hydroxide) steel is widely used in sodium hydroxide solution below 80 ℃, 30% concentration, there are many factories at 100 ℃, 75% below the ordinary steel is still used, although the corrosion increases, but the economy is good . Ordinary stainless steel lye corrosion resistance and cast iron compared with no obvious advantages, as long as the medium allows a small amount of iron content is not recommended for incorporation of stainless steel. For high temperature alkaline use of titanium and titanium alloy or high alloy stainless steel. The company generally cast iron pump can be used for low temperature lye concentration, special requirements can be used when all kinds of stainless steel pump or fluorine plastic pump. 6. Ammonia (ammonia hydroxide) Most metals and non-metals in liquid ammonia and ammonia (ammonia hydroxide) corrosion are minor, only copper and copper alloy should not be used. Most of the company's products for ammonia and ammonia transport. 7. Saline (seawater) Common steel corrosion rate in sodium chloride solution and seawater, salt water is not too high, the general shall be used paint protection; various types of stainless steel also have a low uniform corrosion rate, but may be due to chloride ions caused by the local Corrosion, usually 316 stainless steel is better. Various types of chemical companies have 316 material pump configuration. 8. alcohols, ketones, esters, ethers Common alcohol mediums are methanol, ethanol, ethylene glycol, propanol, ketones have acetone, butanone and so on, the ester medium has a variety of methyl esters, Ethyl ether, ethers medium ether, ether, butyl ether, they are basically non-corrosive, common materials are applicable, the specific selection should also 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. 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. Cooling problems The delivery of high-temperature media sets higher requirements for the pump's construction, materials, and ancillary systems. Here are some of the different cooling requirements for temperature changes and the company's application of pumps: 1. For media temperatures below 120 ° C, Usually do not set a special cooling system, use more of their own medium to lubricate and cool. DFL (W) H chemical pump, DFL (W) PH shield chemical pump (class H should be used for shielded motor over 90 ℃); DFCZ common type and IH chemical pump can make the temperature Up to 140 ℃ ~ 160 ℃; IHF lined with fluorine pump up to a maximum temperature of 200 ℃; only CQB ordinary magnetic pump temperature does not exceed 100 ℃. It is worth mentioning that for the easy-to-crystallize or media containing particles should be equipped with a sealing surface flushing pipe (design have left interface). 2. For media above 120 ° C and within 300 ° C, a cooling chamber is normally to be provided on the pump cover and the seal chamber is also to be filled with coolant (to be fitted with a double-ended mechanical seal). When coolant is not allowed to penetrate the medium , It should be taken after the cooling medium itself access (through a simple heat exchanger). The company has DFCZ chemical process pump, GRG high temperature pipeline pump and HPK hot water circulating pump (under development) to choose from, the other CQB-G high temperature magnetic pump can be used within 280 ℃ high temperature medium. 3 for more than 300 ℃ high temperature medium, not only need to cool the pump head part, the suspension bearing chamber should also be equipped with cooling system, the pump structure is generally the central support form, the mechanical seal is best to use metal bellows type, but the price is high The price is more than 10 times the ordinary mechanical seal). At present the company only DFAY centrifugal pump temperature can reach 420 ℃ (under development). Sealing problems No leakage is the eternal pursuit of chemical equipment, it is this requirement contributed to the growing use of magnetic pumps and shielded pumps. However, there is still a long way to go without leakage, such as the life span of the magnetic pump isolation sleeve and shielding pump shielding sleeve, the material pitting problem, the reliability of static sealing, and the like. Now on the sealing of some of the basic situation is briefly described as follows: 1. Seal For the static seal, seal and seal are usually only two forms, and O-ring seal again the most widely used; for the dynamic seal, chemical Pumps rarely use packing seals, mainly mechanical seals, mechanical seals have a single end and double end, balanced and unbalanced points, balanced for high pressure medium seal (usually refers to the pressure greater than 1.0MPa), double End machine seal is mainly used for high temperature, easy to crystallize, 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 ~ 0.1MPa. 2. Sealing material Chemical pump static sealing materials generally use fluorine rubber, special circumstances only use PTFE material; mechanical seal ring static material configuration is more critical, not cemented carbide is the best on the cemented carbide, the price is high On the one hand, the hardness difference between the two is not reasonable, so it is best to distinguish between media characteristics. (Note: The American Petroleum Institute API 610 Eighth Edition typical configuration of mechanical seals and piping systems are detailed in Appendix D) Viscosity problems The viscosity of the medium on the performance of the pump is very large, when the viscosity increases , Pump head curve down, the best conditions of the head and flow are decreased, while the power is then increased, thus reducing 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 pulp, paste and viscous liquid delivery, the proposed selection of screw pump, the company DFGG single screw pump medium viscosity up to 1000000cst.