Apr. 02, 2024
1. Flow rate is one of the important performance data for pump selection. It is directly related to the production capacity and delivery capacity of the entire device. For example, in the process design of the design institute, the normal, minimum and maximum flow rates of the pump can be calculated. When selecting a pump, take the maximum flow rate as the basis and take into account the normal flow rate. When there is no maximum flow rate, 1.1 times the normal flow rate can usually be taken as the maximum flow rate.
2. The head required by the installation system is another important performance data for pump selection. Generally, the head should be enlarged by 5% to 10% to select the type.
3. Liquid properties, including the name of the liquid medium, physical properties, chemical properties and other properties. The physical properties include temperature c, density d, viscosity u, solid particle diameter and gas content in the medium, etc. This involves the head of the system, effective gas Erosion allowance calculation and suitable pump type: Chemical properties, mainly referring to the chemical corrosiveness and toxicity of the liquid medium, are important basis for selecting pump materials and which type of shaft seal to use.
4. The pipeline layout conditions of the device system refer to the liquid delivery height, liquid delivery distance, liquid delivery direction, the lowest liquid level on the suction side, the highest liquid level on the discharge side, and other data as well as pipeline specifications and their length, materials, pipe fitting specifications, and quantity. etc., in order to calculate the system comb head and check the NPSH.
5. There are many contents of operating conditions, such as liquid operation T saturated steam force P, suction side pressure PS (absolute), discharge side container pressure PZ, altitude, ambient temperature, whether the operation is intermittent or continuous, and whether the pump position is fixed. It's still removable.
Corrosion has always been one of the most troublesome hazards of chemical equipment. If you are not careful, it may damage the equipment, or cause accidents or even disasters. According to relevant statistics, about 60% of the damage to chemical equipment is caused by corrosion. Therefore, when selecting a chemical pump, you must first pay attention to the scientific nature of material selection. There is usually a misunderstanding that stainless steel is a "universal material". It is very dangerous to use stainless steel regardless of the medium and environmental conditions. Let’s talk about the key points of material selection for 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 uses. The corrosion of materials by sulfuric acid at different concentrations and temperatures is quite different. For concentrated sulfuric acid with a concentration above 80% and a temperature less than 80°C, carbon steel and cast iron have good corrosion resistance, but they are not suitable for high-speed flowing sulfuric acid. It is not suitable for use as a material for pump valves; ordinary stainless steel such as 304 (0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti) also has limited use for 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) and high-alloy stainless steel (No. 20 alloy). Fluorine plastic has good sulfuric acid resistance, and using a fluorine-lined pump (F46) is a more economical choice. The company's applicable products include: IHF fluorine-lined pumps, PF (FS) strong corrosion-resistant centrifugal pumps, CQB-F fluorine plastic magnetic pumps, etc.
2. Hydrochloric acid: Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and molybdenum-containing high-silicon ferrosilicon can only be used in hydrochloric acid below 50°C and 30%. Contrary to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so rubber-lined pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choices for transporting hydrochloric acid. The company's applicable products include: IHF fluorine-lined pumps, PF (FS) strong corrosion-resistant centrifugal pumps, CQ polypropylene magnetic pumps (or fluorine plastic magnetic pumps), etc.
3. Nitric acid. Most general metals are rapidly corroded and destroyed in nitric acid. Stainless steel is the most widely used nitric acid-resistant material. It has good corrosion resistance to all concentrations of nitric acid at room temperature. It is worth mentioning that stainless steel containing molybdenum (such as The corrosion resistance of 316, 316L) to nitric acid is not only no better than that of ordinary stainless steel (such as 304, 321), but sometimes even worse. For high-temperature nitric acid, titanium and titanium alloy materials are usually used. The company's applicable products include: DFL(W)H chemical pump, DFL(W)PH shielded chemical pump, DFCZ process pump, DFLZP self-priming chemical pump, IH chemical pump, CQB magnetic pump, etc. The material is 304.
4. Acetic acid is one of the most corrosive substances among organic acids. Ordinary steel will be severely corroded in acetic acid at all concentrations and temperatures. Stainless steel is an excellent acetic acid-resistant material. 316 stainless steel containing molybdenum can also be used in high temperatures and Dilute acetic acid vapor. For demanding requirements such as high temperature, high concentration acetic acid or other corrosive media, high alloy stainless steel or fluoroplastic pumps can be selected.
5. Alkali (sodium hydroxide): Steel is widely used in sodium hydroxide solutions below 80°C and with a concentration of 30%. There are also many factories that still use ordinary steel at temperatures below 100°C and 75%. Although corrosion increases, the economy is good. . The corrosion resistance of ordinary stainless steel to alkali liquid has no obvious advantage compared with cast iron. As long as a small amount of iron is allowed to be incorporated into the medium, stainless steel is not recommended. For high-temperature alkaline solutions, titanium and titanium alloys or high-alloy stainless steel are often used. The company's general cast iron pumps can be used for low-concentration alkaline liquids at room temperature. Various stainless steel pumps or fluoroplastic pumps can be used when special requirements are required.
6. Ammonia (ammonium hydroxide): Most metals and non-metals corrode very slightly in liquid ammonia and ammonia (ammonium hydroxide). Only copper and copper alloys should not be used. Most of the company's products are suitable for the transportation of ammonia and ammonia water.
7. Salt water (sea water) The corrosion rate of ordinary steel in sodium chloride solution, sea water, and salt water is not very high, and generally must be protected by coatings; various types of stainless steel also have very low uniform corrosion rates, but localized corrosion may be caused by chloride ions. For corrosion, 316 stainless steel is usually better. The company's various chemical pumps are equipped with 316 materials.
8. Alcohols, ketones, esters and ethers. Common alcohol media include methanol, ethanol, ethylene glycol, propanol, etc.; ketone media include acetone, methyl ethyl ketone, etc.; ester media include various methyl esters, Ethyl ether, etc. Ether media include methyl ether, ethyl ether, butyl ether, etc. They are basically non-corrosive and can be used with commonly used materials. The specific selection should be based on the properties of the medium and related requirements. Reasonable selection should be made. It is also worth noting that ketones, esters, and ethers are soluble in a variety of rubbers, so avoid mistakes when selecting sealing materials.
Generally, the leakage in the pipeline system of industrial pumps can be ignored in the process flow, but the impact on the flow rate when the process changes must be considered. If agricultural pumps use open channels to transport water, leakage and evaporation must also be considered.
Pressure: suction pool pressure, drainage pool pressure, pressure difference (head loss) in the pipeline system.
Pipeline system data (pipe diameter, length, type and number of pipe accessories, geometric elevation from suction pool to pressure pool, etc.).
If necessary, the device characteristic curve should also be drawn.
When designing and laying out pipelines, the following matters should be noted:
A. Choose the pipe diameter reasonably. A large pipe diameter will have a small liquid flow speed and a small resistance loss at the same flow rate. However, the price is high and the pipe diameter is small, which will cause a sharp increase in resistance loss and increase the head of the selected pump. As the belt power increases, the cost and operating expenses increase. Therefore, it should be considered comprehensively from a technical and economic perspective.
B. The discharge pipe and its pipe joints should consider the maximum pressure they can withstand.
C. The pipeline layout should be as straight as possible, minimize the accessories in the pipeline and shorten the length of the pipeline. When it is necessary to turn, the bending radius of the elbow should be 3 to 5 times the diameter of the pipeline, and the angle should be as large as 90 degrees. ℃.
D. The discharge side of the pump must be equipped with valves (ball valves or stop valves, etc.) and check valves. The valve is used to adjust the operating point of the pump. The check valve prevents the pump from reversing when the liquid flows back and protects the pump from water hammer. (When the liquid flows back, it will generate huge reverse pressure and damage the pump)
Determination of flow rate
A. If the minimum, normal and maximum flow rates have been given in the production process, the maximum flow rate should be considered.
B. If only normal flow is given in the production process, a certain margin should be considered.
For ns100 large-flow low-lift pumps, the flow margin is 5%. For ns50 small-flow high-lift pumps, the flow margin is 10%. For pumps with 50≤ns≤100, the flow margin is also 5%. For quality For inferior pumps and poor operating conditions, the flow margin should be 10%.
C. If the basic data only gives weight flow rate, it should be converted into volume flow rate.
The transportation of high-temperature media puts forward higher requirements on the structure, materials and auxiliary systems of the pump. Let’s talk about the cooling requirements of different temperature changes and the company’s applicable pump types:
1. For media with a temperature lower than 120°C, a special cooling system is usually not set up, and the own medium is often used for lubrication and cooling. Like DFL(W)H chemical pumps and DFL(W)PH shielded chemical pumps (the protection level of the shielded motor should be H level when it exceeds 90°C); while the DFCZ ordinary type and IH chemical pumps adopt a suspension structure that can reduce the temperature The upper limit reaches 140℃~160℃; the maximum operating temperature of IHF fluorine-lined pump can reach 200℃; only the operating temperature of CQB ordinary magnetic pump does not exceed 100℃. It is worth mentioning that media that is prone to crystallization or contains particles should be equipped with sealing surface flushing pipelines (interfaces are left in the design).
2. For media with temperatures above 120°C and within 300°C, a cooling chamber must generally be provided on the pump cover, and the sealing chamber should also be connected to the coolant (must be equipped with a double-end mechanical seal). When the coolant is not allowed to penetrate into the medium , the medium itself should be cooled and then connected (can be achieved through a simple heat exchanger). At present, the company has DFCZ 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 within 280°C.
3. For high-temperature media above 300°C, not only the pump head part needs to be cooled, but also the suspension bearing chamber should be equipped with a cooling system. The pump structure is generally in the form of a central support. The mechanical seal is preferably a metal bellows type, but the price is high ( The price is more than 10 times that of ordinary machine seals). At present, the company only has the DFAY centrifugal oil pump that can reach a service temperature of 420°C (under development).
No leakage is the eternal pursuit of chemical equipment. It is this requirement that has contributed to the increasing application of magnetic pumps and canned pumps. However, there is still a long way to go to truly achieve no leakage, such as the life problems of the magnetic pump isolation sleeve and the canned pump shield sleeve, the pitting corrosion problem of the material, the reliability of the static seal, etc. Now let’s briefly introduce some basic information about sealing.
1. Seal form For static seals, there are usually only two forms: gaskets and sealing rings, and O-rings are the most widely used sealing rings; for dynamic seals, chemical pumps rarely use packing seals, and mechanical seals are the main ones. , Mechanical seals can be divided into single-end face and double-end face, balanced type and unbalanced type. The balanced type is suitable for sealing of high-pressure media (usually refers to pressure greater than 1.0MPa). The double-end mechanical seal is mainly used for high temperature, easy to crystallize, and hazardous materials. For media with high viscosity, particles and toxic volatilization, the double-end mechanical seal should inject isolation liquid into the seal cavity, and its pressure is generally 0.07~0.1MPa higher than the medium pressure.
2. Sealing material. The material of the static seal of chemical pumps is generally fluorine rubber, and polytetrafluoroethylene is used in special cases. The material configuration of the dynamic and static rings of the mechanical seal is more critical. It is not that cemented carbide is the best over cemented carbide because of the high price. On the one hand, it is unreasonable that there is no difference in hardness between the two, so it is best to treat them differently according to the characteristics of the medium.
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