How to select chemical pumps

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How to choose a chemical pump? The petrochemical industry holds a very important position in the national economy, and chemical process pumps, as key supporting equipment, are attracting increasing attention. Given the complex nature of chemical media, along with the ever-rising demands from users, how should we choose the appropriate products as manufacturers? What aspects should be given special attention? …Waiting, etc., is particularly important. Based on the characteristics of the company’s relevant products as well as my limited understanding, I would like to provide a brief overview of the selection process for common chemical pumps, in the hope that it will be helpful for colleagues to carry out their work better in this field. Corrosion issues 　　Corrosion has always been one of the most troublesome hazards for chemical processing equipment; even a slight carelessness can lead to equipment damage, and in severe cases, it can result in accidents or even disasters. According to relevant statistics, about 60% of the damage to chemical processing equipment is caused by corrosion; therefore, when selecting chemical pumps, it is essential to pay attention to the scientific choice of materials. There is a common misconception that stainless steel is an ”**** material” – that it is the best choice in any medium or under any environmental conditions; this is very dangerous. Below are the key points for material selection when dealing with some commonly used chemical media: 1. Sulfuric acid As one of the highly corrosive media, sulfuric acid is an important industrial raw material with a wide range of applications. Sulfuric acid at different concentrations and temperatures causes varying degrees of corrosion to materials. For concentrated sulfuric acid with a concentration of over 80% and a temperature below 80°C, carbon steel and cast iron exhibit good corrosion resistance; however, it is not suitable for sulfuric acid that flows at high speeds, and thus cannot be used as material for pumps and valves ； Common stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) also have limited applicability in sulfuric acid media. Therefore, pump valves for transporting sulfuric acid are usually made of high-silicon cast iron (which is difficult to cast and process) or highly alloyed stainless steel (grade 20 alloy). Fluoroplastics exhibit good resistance to sulfuric acid, making the use of fluorinated-lined pumps (F46) a more economical option. The company’s applicable products include IHF fluorine-lined pumps, PF(FS) highly corrosion-resistant centrifugal pumps, CQB-F fluoroplastic magnetic pumps, and more. 　　2. Hydrochloric acid: The vast majority of metal materials are not resistant to corrosion by hydrochloric acid (including various stainless steel materials); high-molybdenum high-silicon iron can only be used in hydrochloric acid at temperatures below 50°C and concentrations of 30% or less. Unlike metal materials, the vast majority of non-metallic materials exhibit good corrosion resistance to hydrochloric acid; therefore, rubber-lined pumps and plastic pumps (such as those made of polypropylene or fluoroplastics) are the best choices for transporting hydrochloric acid. The company’s applicable products include: IHF fluorine-lined pumps, PF(FS) highly corrosion-resistant centrifugal pumps, CQ polypropylene magnetic pumps (or fluoroplastic magnetic pumps), etc. 　　3. Nitric acid Most metals are rapidly corroded and damaged by nitric acid. Stainless steel is the most widely used material resistant to nitric acid; it exhibits good corrosion resistance to nitric acid at all concentrations at room temperature. It is worth noting that stainless steels containing molybdenum (such as 316 and 316L) do not have better corrosion resistance to nitric acid than ordinary stainless steels (such as 304 and 321), and in some cases their resistance is even lower. For high-temperature nitric acid, titanium and titanium alloy materials are commonly used. The company’s applicable products include: DFL(W)H chemical pumps, DFL(W)PH shielded chemical pumps, DFCZ process pumps, DFLZP self-priming chemical pumps, IH chemical pumps, CQB magnetic pumps, etc., all made of 304 material. 　　4. Acetic acid: It is one of the most corrosive organic acids; ordinary steel is severely corroded by acetic acid at all concentrations and temperatures. Stainless steel is an excellent material resistant to acetic acid, and 316 stainless steel containing molybdenum can also be used in high-temperature environments as well as with dilute acetic acid vapors. For demanding applications such as high-temperature, high-concentration acetic acid or environments containing other corrosive agents, high-alloy stainless steel or fluoroplastic pumps can be used. 　　5. Bases (sodium hydroxide) Steel is widely used in sodium hydroxide solutions at temperatures below 80°C and with concentrations up to 30%. Many factories still use ordinary steel at temperatures of 100°C and concentrations below 75%; although corrosion increases, it remains cost-effective. Ordinary stainless steel does not have a significant advantage over cast iron in terms of corrosion resistance to alkaline solutions; it is not recommended to use stainless steel when only a small amount of iron is allowed to be present in the medium. For high-temperature alkaline solutions, titanium and titanium alloys or highly alloyed stainless steels are commonly used. The company’s standard cast-iron pumps can be used for alkaline solutions at normal temperatures and low concentrations; for special requirements, various stainless steel pumps or fluoroplastic pumps can be employed. 　　6. Ammonia (ammonium hydroxide) Most metals and non-metals suffer only mild corrosion in liquid ammonia and ammonium hydroxide solutions; only copper and its alloys are not suitable for use in such environments. Most of the company’s products are suitable for transporting ammonia and ammonia water. 　　7. Saltwater (seawater) Ordinary steel experiences a low rate of corrosion in sodium chloride solutions as well as in seawater and brackish water; coating protection is generally required ； Various types of stainless steel also have very low uniform corrosion rates, but local corrosion may occur due to chloride ions; therefore, 316 stainless steel is generally the better choice. All types of chemical pumps produced by the company are available in 316 material configuration. 　　8. Alcohols, alkanes, esters, ethers Common alcohol-based media include methanol, ethanol, ethylene glycol, propanol, etc.; alkanes include propane, butane, etc.; ester-based media comprise various methyl esters, ethyl esters, etc.; ether-based media include methyl ether, ethyl ether, butyl ether, etc. These substances have little corrosive effect, and most common materials can be used with them. When making a selection, it is necessary to consider the properties of the medium as well as relevant requirements in order to make a proper choice. It is also worth noting that alcohols, esters, and ethers are soluble in various rubbers, which helps to avoid mistakes when selecting sealing materials. 　　There are many other media that cannot be listed here one by one. In short, when selecting materials, one should not act casually or blindly; instead, it is necessary to consult relevant information and draw on proven experience. Cooling issues The transportation of high-temperature media places higher demands on the pump’s structure, materials, and auxiliary systems. Below are the cooling requirements associated with different temperature levels, as well as the types of pumps suitable for use in such applications: 1. For media with temperatures below 120°C, a dedicated cooling system is usually not necessary; the medium itself is often used for lubrication and cooling purposes. Such as DFL(W)H chemical pumps, DFL(W)PH shielded chemical pumps (for temperatures above 90°C, the protection class of the shielded motor should be H grade) ； The standard version of DFCZ and IH chemical pumps can achieve an upper temperature limit of 140°C to 160°C thanks to their suspension structure℃ ； IHF fluoroplastic pump* can reach a maximum operating temperature of 200℃ ； Only the ordinary CQB magnetic pump is designed for use at temperatures not exceeding 100°C. It is worth mentioning that media that are prone to crystallization or contain particles should be equipped with a sealing surface flushing pipeline (interfaces are provided during design). 　　2. For media with temperatures above 120°C and below 300°C, a cooling chamber is generally required on the pump cover, and the sealing chamber should also be connected to coolant (a double-end face mechanical seal is necessary). When it is not allowed for coolant to penetrate into the medium, the medium itself should be cooled before being fed in (this can be achieved using a simple heat exchanger). Currently, the company offers DFCZ-type chemical process pumps, GRG high-temperature pipeline pumps, and HPK hot water circulation pumps (under development) for selection; in addition, the CQB-G high-temperature magnetic pump can be used for high-temperature media up to 280°C. 　　3. For high-temperature media above 300°C, not only the pump head but also the suspension bearing chamber requires a cooling system. The pump structure is generally of a central support type, and mechanical seals**** use metal diaphragm types; however, they are expensive (their cost is more than 10 times that of ordinary mechanical seals). Currently, only the DFAY centrifugal oil pump in the company can reach a operating temperature of 420°C (under development). Sealing issues 　　Zero leakage is an eternal goal for chemical processing equipment, and it is precisely this requirement that has led to the increasing use of magnetic pumps and shielded pumps. However, there is still a long way to go before true leaklessness can be achieved, such as the lifespan issues of magnetic pump isolation sleeves and shielded pump shielding sleeves, the problem of pitting in materials, and the reliability of static seals, among others. Here is a brief introduction to some basic aspects of sealing: 1. Sealing types. For static sealing, there are generally only two types: gaskets and seals, with O-rings being the most widely used type of seal ； For dynamic seals, chemical pumps rarely use packing seals; mechanical seals are preferred instead. Mechanical seals come in single-face and double-face types, as well as balanced and unbalanced versions. Balanced mechanical seals are suitable for sealing high-pressure media (typically those with pressures greater than 1.0 MPa). Double-face mechanical seals are used primarily for media that are high-temperature, prone to crystallization, viscous, contain particles, or are toxic and volatile. An isolation fluid must be injected into the sealing chamber using double-face mechanical seals, and its pressure is usually 0.07–0.1 MPa higher than that of the medium. 　　2. Sealing materials 　　Fluororubber is generally used as the material for the static seals of chemical pumps; polytetrafluoroethylene is employed only in special cases ； The material selection for the stationary and rotating rings of mechanical seals is quite important. It’s not true that one carbide material must be used against another; high costs are one factor, but it’s also unreasonable if there is no difference in hardness between the two materials. Therefore, the choice of materials should be determined based on the characteristics of the medium being handled. 　　(Note: Appendix D of API 610, eighth edition, provides detailed specifications for the typical configurations of mechanical seals and piping systems.) Viscosity issues The viscosity of the fluid has a significant impact on the performance of the pump; as viscosity increases, the pump’s head curve declines. As a result, both the head and flow rate at operating conditions decrease, while power consumption increases, leading to reduced efficiency. The parameters for normal samples represent the performance when transporting clean water; conversions are required when transporting viscous media (the correction factors for different viscosities can be found in the relevant conversion tables). For the transfer of slurries, pastes, and viscous fluids with high viscosity, it is recommended to use screw pumps; the DFGG single-screw pump offered by the company can handle media with viscosities up to