Common problems of chemical process pumps and selection methods

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The transportation of high-temperature media places higher demands on the pump’s structure, materials, and auxiliary systems. Below, we discuss 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 required; instead, the medium itself is used for lubrication and cooling. 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℃ ； The maximum operating temperature for IHF fluoroplastic pumps can reach 200℃ ； Only the ordinary CQB magnetic pump is designed for use at temperatures not exceeding 100°C. It is worth noting 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. For high-temperature media above 300°C, not only must the pump head be cooled, but a cooling system must also be installed in the bearing housing; the pump structure is generally of a central support type, and metal bellows-type mechanical seals are preferred, although they are expensive (their price is more than 10 times that of ordinary mechanical seals). Currently, DFAY centrifugal oil pumps can operate at temperatures up to 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 usually only two types: gaskets and seals, with O-rings being the most widely used type of seal ； For dynamic sealing, 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 mainly 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 the pressure of the medium. 　　2. Sealing materials 　　Fluororubber is generally used as the material for the static seals of chemical pumps; polytetrafluoroethylene is used 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 combination of cemented carbide materials is always the best; high costs are one issue, but it’s also unreasonable if there’s no difference in hardness between the two materials. Therefore, it’s best to choose materials based on the characteristics of the medium being handled. (Note: API 610, 8th edition, provides detailed specifications for typical configurations of mechanical seals and piping systems in Appendix D.)
Viscosity issue
The viscosity of the medium has a significant impact on the performance of pumps. As viscosity increases, the pump’s head curve declines, and both the optimal head and flow rate decrease as well. At the same time, the power required by the pump increases, resulting in reduced efficiency. The parameters for typical 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 liquids with high viscosity, it is recommended to use screw pumps; the company’s DFGG single-screw pumps can handle media with a viscosity of up to 1,000,000 cSt.