The pump is a general-purpose mechanical equipment with a wide range of applications. It is widely used in petroleum, chemical, electric metallurgy, mining, shipbuilding, light industry, agriculture, civil and defense sectors, and plays an important role in the national economy. The power consumption of the pump accounts for more than 21% of the national electricity consumption.
Therefore, greatly reducing the energy consumption of the pump is of great significance for saving energy. In recent years, our pump industry has designed and developed many energy-efficient products, such as IHF, CQB, FSB, UHB and other pump products, which have played a positive role in reducing pump energy consumption.
A. Basic data of pump selection
1. Characteristics of the medium: medium name, specific gravity, viscosity, corrosivity, toxicity, etc.
2. The particle diameter and content of the solids contained in the medium.
3. Medium temperature: (°C)
4. The required flow rate The general industrial pump can ignore the leakage in the pipeline system in the process flow, but must consider the impact on the flow when the process changes. Agricultural pumps that use open channels should also consider leakage and evaporation.
5. Pressure: suction tank pressure, drain pressure, pressure drop in the piping system (head loss).
6. Pipeline system data (pipe diameter, length, type and number of pipe attachments, geometric elevation of sink to pressure tank, etc.).
The device characteristic curve should also be made if necessary. When designing the layout of the pipeline, you should pay attention to the following items:
1. Reasonably choose the diameter of the pipeline. The diameter of the pipeline is large. Under the same flow rate, the flow velocity is small, the resistance loss is small, but the price is high. The diameter of the pipeline is small, which will lead to a sharp increase in the resistance loss, which will increase the lift of the selected pump. With increased power, both cost and operating costs increase. Therefore, it should be considered from a technical and economic perspective.
2. The discharge pipe and its pipe joints should take into account the maximum pressure that can be withstood.
3. The pipeline layout should be arranged as straight pipe as much as possible, minimize the attachments in the pipeline and minimize the length of the pipeline. When turning, 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. °.
4. The discharge side of the pump must be equipped with a valve (ball valve or shut-off valve, etc.) and a check valve. The valve is used to adjust the operating point of the pump. The check valve prevents the pump from reversing when the liquid is reversed, and prevents the pump from hitting the water hammer. (When the liquid flows backwards, it will generate a huge reverse pressure, which will damage the pump)
B. Determination of the flow head
1. If the minimum, normal, and maximum flow rates have been given in the production process, the maximum flow rate should be considered.
2. If only normal flow is given in the production process, consideration should be given to leaving a certain margin. For the large flow low lift pump with ns>100, the flow balance is 5%, for the small flow high lift pump with ns<50, the flow balance is 10%, the pump with 50≤ns≤100, the flow balance is also 5 %, for pumps of poor quality and poor operating conditions, the flow margin should be 10%.
3. If the basic data only gives weight flow, it should be converted into volume flow.
C. Basic basis
1. Flow rate is one of the important performance data of the pump selection, which is directly related to the production capacity and conveying capacity of the entire device. For example, the normal, minimum and maximum flow rates of the pump can be calculated in the design of the design institute. When the pump is selected, the normal flow rate is based on the maximum flow rate. When there is no maximum flow rate, 1.1 times the normal flow rate can be taken as the maximum flow rate.
2. The head required for the installation system is another important performance data of the pump selection. Generally, the head should be selected by amplifying the 5%~10% balance.
3. Liquid properties, including liquid media name, physical properties, chemical properties and other properties, physical properties are temperature c density d, viscosity u, solid particle diameter and gas content in the medium, etc., which relates to the lift of the system, effective gas Calculation of the amount of eclipse and the type of suitable pump: chemical properties, mainly refers to the chemical corrosiveness and toxicity of the liquid medium, is an important basis for the selection of the pump material and the type of shaft seal.
4. The pipeline arrangement conditions of the equipment system refer to the data of the liquid feeding height, the liquid feeding distance, the lowest liquid level on the suction side, the highest liquid level on the discharge side, and other data and pipe specifications and their lengths, materials, pipe fittings specifications and quantities. Etc., in order to carry out the calculation of the combing process and the checking of the NPSH.
5. Operating conditions have many contents, such as liquid operation T saturated steam force P, suction side pressure PS (absolute), discharge side container pressure PZ, altitude, ambient temperature operation is gap or continuous, pump position is fixed Still removable.
D. Corrosion effects
Corrosion has always been one of the most headaches of chemical equipment. If it is slightly careless, it will damage the equipment and cause accidents and even disasters. According to relevant statistics, about 60% of the destruction of chemical equipment is caused by corrosion. Therefore, in the selection of chemical pumps, we must first pay attention to the scientific nature of material selection. There is usually a misunderstanding that stainless steel is a “universal material” and it is dangerous to hold stainless steel regardless of the medium and environmental conditions. Here are some key points for material selection for some common chemical media:
1. Sulfuric acid
As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of uses. Different concentrations and temperatures of sulfuric acid have a great difference in corrosion of materials. For concentrated sulfuric acid with a concentration above 80% and temperature less than 80 °C, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. It is not suitable as a material for pump valves; ordinary stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) are also limited in their use for sulfuric acid media. Therefore, the pump valve for conveying sulfuric acid is usually made of high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (20 alloy). Fluoroplastics have good sulfuric acid resistance, and the use of a fluorine-lined pump (F46) is a more economical option. The company's applicable products are: IHF lining fluorine pump, PF (FS) strong corrosion resistant centrifugal pump, CQB-F fluoroplastic magnetic pump.
2. Hydrochloric acid
Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and molybdenum-containing high-silicon iron can only be used for hydrochloric acid at 50 ° C and 30%. Contrary to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so rubber pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choice for transporting hydrochloric acid. The company's applicable products are: IHF lining fluorine pump, PF (FS) strong corrosion resistant centrifugal pump, CQ polypropylene magnetic pump (or fluoroplastic magnetic pump).
3. Nitric acid
Generally, most metals are quickly 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 normal temperature. It is worth mentioning that it contains molybdenum-containing stainless steel (such as 316 and 316L). The 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, titanium and titanium alloy materials are usually used. The company's applicable products are: DFL (W) H chemical pump, DFL (W) PH shielding chemical pump, DFCZ process pump, DFLZP self-priming chemical pump, IH chemical pump, CQB magnetic pump, etc., the material is 304.
4. Acetic acid
One of the most corrosive substances in organic acids, ordinary steel is severely corroded in acetic acid of all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material. Molybdenum-containing 316 stainless steel can also be used for high temperature and dilute acetic acid vapor. High-alloy stainless steel or fluoroplastic pumps are available for demanding requirements such as high temperature, high concentration acetic acid or other corrosive media.
5. Alkali (sodium hydroxide)
Steel is widely used in sodium hydroxide solutions below 80 ° C and 30% concentration. Many factories still use ordinary steel at 100 ° C and below 75%. Although the corrosion is increased, the economy is good. The corrosion resistance of ordinary stainless steel to lye has no obvious advantages compared with cast iron. Stainless steel is not recommended as long as a small amount of iron is allowed in the medium. For high-temperature alkaline liquids, titanium and titanium alloys or high-alloy stainless steels are often used. The company's general cast iron pumps can be used for low-concentration lye at normal temperature. For special requirements, all kinds of stainless steel pumps or fluoroplastic pumps can be used.
6. Ammonia (ammonium hydroxide)
Most metals and non-metals are slightly corrosive in liquid ammonia and ammonia (ammonium hydroxide), and only copper and copper alloys are not suitable. Most of the company's products are suitable for the transportation of ammonia and ammonia.
7. Salt water (sea water)
Ordinary steel in the sodium chloride solution and seawater, salt water corrosion rate is not too high, generally must be protected by paint; 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 better. The company's various chemical pumps have 316 material configurations.
8. Alcohols, ketones, esters, ethers, common alcohols are methanol, ethanol, ethylene glycol, propanol, etc., ketone media are acetone, methyl ethyl ketone, etc., ester media have various methyl esters, Ethyl ester, etc., ether medium is methyl ether, ether, dibutyl ether, etc., they are basically non-corrosive, common materials can be applied, and specific selection should also make reasonable choice according to the properties of the medium and related requirements. It is also worth noting that ketones, esters, and ethers are soluble in a variety of rubbers and avoid errors when selecting sealing materials.
E. Other factors affect
General industrial pumps can ignore the amount of leakage in the piping system during the process, but must consider the impact of the process on the flow. Agricultural pumps that use open channels should also consider leakage and evaporation.
Pressure: sink pressure, drain pressure, pressure differential in the piping system (head loss).
Pipe system data (pipe diameter, length, type and number of pipe attachments, geometric elevation of the sink to the pressure tank, etc.).
The device characteristic curve should also be made if necessary.
F. Impact of the pipeline
When designing the layout of the pipeline, you should pay attention to the following items:
1. Reasonably choose the diameter of the pipeline, the diameter of the pipeline is large, the flow velocity is small, the resistance loss is small, but the price is high, and the diameter of the pipeline is small, which will lead to a sharp increase in the resistance loss and increase the lift of the selected pump. With increased power, both cost and operating costs increase. Therefore, it should be considered from a technical and economic perspective.
2. The discharge pipe and its pipe joints should take into account the maximum pressure that can be withstood.
3. The pipe arrangement should be arranged as a straight pipe as much as possible. Minimize the accessories in the pipe and minimize the length of the pipe. When turning, the bending radius of the elbow should be 3 to 5 times the diameter of the pipe, and the angle should be as large as 90. °C.
4. The discharge side of the pump must be equipped with a valve (ball valve or shut-off valve, etc.) and a check valve. The valve is used to adjust the operating point of the pump. The check valve prevents the pump from reversing when the liquid is reversed, and prevents the pump from hitting the water hammer. (When the liquid flows backwards, it will generate a huge reverse pressure, which will damage the pump)
G. Impact of the flow head
1. If the minimum, normal, and maximum flow rates have been given in the production process, the maximum flow rate should be considered.
2. If only normal flow is given in the production process, consider leaving a certain margin. For the ns100 high-flow low-lift pump, the flow margin is 5%, for the small-flow high-lift pump of ns50, the flow balance is 10%, the pump with 50≤ns≤100, the flow margin is also 5%, the quality For pumps that are inferior and have poor operating conditions, the flow margin should be 10%.
3. If the basic data is only for weight flow, it should be converted to volume flow.
H. Effect of temperature
The transportation of high-temperature medium puts higher requirements on the structure, materials and auxiliary system of the pump. Let's talk about the cooling requirements of different temperature changes and the company's applicable pump type:
1. For media with a temperature lower than 120 °C, there is usually no special cooling system, and the medium itself is used for lubrication and cooling. Such as DFL (W) H chemical pump, DFL (W) PH shielding chemical pump (protection level of shielded motor should exceed H grade when over 90 °C); and DFCZ common type and IH chemical pump can use temperature to adopt suspension structure The upper limit is 140 ° C ~ 160 ° C; IHF lining fluorine pump can be used up to 200 ° C; only CQB ordinary magnetic pump use temperature does not exceed 100 ° C. It is worth mentioning that the medium that is easy to crystallize or contains particles should be equipped with a sealing surface flushing line (designed with an interface).
2. For mediums above 120 °C and below 300 °C, a cooling chamber shall be provided on the pump cover. The sealing chamber shall also be connected to the coolant (with double mechanical seal), when the coolant is not allowed to penetrate into the medium. It should be taken after cooling its own medium (can be realized by simple heat exchanger). At present, the company has DFCZ type chemical process pump, GRG high temperature pipeline pump and HPK hot water circulation pump (under development), and CQB-G high temperature type magnetic pump can be used for high temperature medium within 280 °C.
3. For high temperature medium 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 a normal machine seal). At present, only the DFAY centrifugal oil pump can reach a temperature of 420 °C (under development).
I. Effect of sealing
No leakage is the eternal pursuit of chemical equipment. It is this requirement that has led to the expansion of the application of magnetic pumps and shielded pumps. However, there is still a long way to go before there is no leakage, such as the life of the magnetic pump isolation sleeve and the shielded pump shield, the pitting problem of the material, the reliability of the static seal, and so on. A brief introduction to some basic aspects of sealing is now available.
1. Sealing form For static sealing, there are usually only two types of gaskets and sealing rings, and the sealing ring is the most widely used O-ring; for dynamic sealing, chemical pumps rarely use packing seals, mainly mechanical seals. The mechanical seal has single-end and double-end, balanced and unbalanced types. The balance type is suitable for high-pressure medium sealing (usually refers to pressure greater than 1.0MPa). Double-faced machine seal is mainly used for high temperature, easy crystallization, and Viscosity, granules and toxic volatilized medium, the double-end machine seal should inject the isolation liquid into the sealed cavity, and the pressure is generally higher than the medium pressure of 0.07~0.1MPa.
2. Sealing material The material of the chemical pump static sealing is generally made of fluororubber. In special cases, the PTFE material is used. The material arrangement of the mechanical seal dynamic and static ring is more important. It is not the hard alloy to the hard alloy, the price is high. On the one hand, it is not reasonable to have no hardness difference between the two, so it is best to treat them differently according to the characteristics of the medium.
J. Effect of viscosity
The viscosity of the medium has a great influence on the performance of the pump. When the viscosity increases, the lift curve of the pump decreases, and the head and flow rate of the optimal working condition decrease, and the power increases, so the efficiency decreases. The parameters on the general sample are the performance when the water is delivered. When the viscous medium is transported, the conversion should be performed (the correction coefficient for different viscosities can be found in the relevant conversion chart). For the transportation of higher viscosity pulp, paste and viscous liquid, it is recommended to use screw pump. The company DFGG single screw pump is suitable for medium viscosity up to 1000000cst.
K. Necessity
Due to unreasonable selection, many pumps are in unreasonable operating conditions, operating inefficiently, and wasting a lot of energy. Other pumps are not suitable for use because of the unreasonable selection, or the maintenance cost is increased, and the economic benefit is low. It can be seen that the rational selection of pumps is also of great significance for energy conservation. The so-called rational selection of pumps is to comprehensively consider the comprehensive technical and economic indicators such as the investment and operating costs of pump units and pumping stations, so that they meet the principles of economy, safety and application. Specifically, there are the following aspects: the flow rate and head requirements must be met, that is, the operating point of the pump (the intersection of the characteristic curve of the device and the performance curve of the pump) is required to be kept in an efficient range, which saves power. It is not easy to damage the machine. The pump selected is small in size, light in weight, inexpensive in cost, and has good characteristics and high efficiency. It has good anti-cavitation performance, which can reduce the excavation depth of the pump house without causing cavitation of the pump, stable operation and long service life. According to the pump selected to build the pumping station, the project investment is small and the operating cost is low.
