How to choose the most suitable pump has always been a concern of chemical workers.
Different occasions, different media, different materials... It seems not so easy to choose the right chemical pump.
This article talks about the knowledge of pump selection, friends in need can collect and forward.
01. Principles of chemical pump selection
To choose a pump, we must first understand and master the principles of chemical pump selection.
1. Make the type and performance of the selected pump meet the requirements of process parameters such as device flow, head, pressure, temperature, cavitation flow, and suction.
2. Must meet the requirements of media characteristics.
For pumps that transport flammable, explosive, toxic, or valuable media, reliable shaft seals or leak-free pumps, such as magnetic drive pumps, diaphragm pumps, and canned pumps, are required.
For pumps that transport corrosive media, the convection parts are required to use corrosion-resistant materials, such as AFB stainless steel corrosion-resistant pumps, and CQF engineering plastic magnetic drive pumps.
For pumps that convey solid particles, the convection parts are required to be made of wear-resistant materials, and the shaft seal should be flushed with clean liquid when necessary.
3. High mechanical reliability, low noise and low vibration.
4. Economically, the total cost of equipment costs, operating costs, maintenance costs and management costs should be taken into account in the lowest.
5. Selection of chemical pumps in common situations:
(1) The centrifugal pump has the characteristics of high speed, small size, light weight, high efficiency, large flow, simple structure, no pulsation of infusion, stable performance, easy operation and convenient maintenance.
(2) When there are metering requirements, use metering pumps.
(3) When the head requirements are very high, the flow is small and there is no suitable small flow high head centrifugal pump to choose from, the reciprocating pump can be used. If the cavitation requirement is not high, the vortex pump can also be used.
(4) When the head is very low and the flow is large, an axial flow pump and a mixed flow pump can be selected.
(5) When the medium viscosity is large (greater than 650~1000mm2/s), consider using a rotor pump or a reciprocating pump (gear pump, screw pump)
(6) When the medium contains 75% air, the flow is small and the viscosity is less than 37.4mm2/s, a vortex pump can be used.
(7) For occasions with frequent start-up or inconvenient pump filling, pumps with self-priming performance should be selected, such as self-priming centrifugal pumps, self-priming vortex pumps, and pneumatic (electric) dedicated pump membrane pumps.
02. Selection basis for chemical pumps
The pump selection basis should be considered from five aspects according to the process flow and water supply and drainage requirements.
1. Flow rate is one of the important performance data of pump selection, it is directly related to the production capacity and conveying capacity of the whole 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 the pump, take the maximum flow as the basis and take into account the normal flow. When there is no maximum flow, 1.1 times the normal flow can usually be taken as the maximum flow.
2. The head required by the installation system is another important performance data for pump selection. Generally, the head should be selected after magnifying 5%-10% of the margin.
3. Liquid properties, including the name of the liquid medium, physical properties, chemical properties and other properties, which involve the lift of the system, the calculation of the effective cavitation allowance, the type of suitable pump, the choice of pump material and the type of shaft seal, etc. .
4. The piping layout conditions of the device system refer to the liquid delivery height, the liquid delivery distance and the liquid delivery direction, the lowest liquid level on the suction side, the highest liquid level on the discharge side, etc. Some data and piping specifications and their length, materials, pipe fitting specifications, and quantity Etc., in order to carry out the combing head calculation and cavitation allowance check.
5. Determination of operating conditions, such as liquid operation T saturated vapor power, suction side pressure (absolute), discharge side container pressure, altitude, ambient temperature, whether the operation is intermittent or continuous, and whether the pump position is fixed or movable of. Both are important basis for selection.
03. Considerations under various conditions
Piping layout of chemical pump
When designing and laying out pipelines, the following items should be noted:
A. Reasonably choose the pipe diameter, the pipe diameter is large, the liquid flow speed is small, the resistance loss is small at the same flow rate, but the price is high, and the pipe diameter is small, which will cause the resistance loss to increase sharply and increase the head of the selected pump. With the increase of belt power, the cost and operating expenses are increased. Therefore, it should be considered from the perspective of technology and economy.
B. The discharge pipe and its pipe joints should consider the maximum pressure it can withstand.
C. The pipeline layout should be as straight as possible, minimize the accessories in the pipeline and minimize the length of the pipeline. When turning is necessary, the bending radius of the elbow should be 3 to 5 times the diameter of the pipeline, and the angle should be greater than 90 ℃.
D. Valves (ball valves or stop valves, etc.) and check valves must be installed on the discharge side of the pump. The valve is used to adjust the working point of the pump. The check valve can prevent the pump from reversing when the liquid is flowing backwards and prevent the pump from being hit by water hammer. (When the liquid flows back, it will produce huge reverse pressure and damage the pump)
The choice of chemical pump sealing
Leak-free is the eternal pursuit of chemical equipment, and it is this requirement that has contributed to the increasing application of magnetic pumps and canned motor pumps.
1. Sealing form
For static sealing, there are usually only two forms of gasket and sealing ring, and the O-ring is the most widely used sealing ring;
For dynamic seals, chemical pumps seldom use packing seals, mainly mechanical seals. Mechanical seals are divided into single end face and double end face, balanced type and unbalanced type. The balanced type is suitable for the sealing of high pressure medium (usually refers to the pressure greater than 1.0MPa), the double end face machine seal is mainly used for high temperature, easy to crystallize, viscosity, particle-containing and toxic volatile media. The double end face machine seal should inject the isolating fluid into the sealed cavity, and its pressure is generally higher than the medium pressure by 0.07~0.1 MPa.
2. Sealing material
Chemical pump static seal materials generally use fluorine rubber, and PTFE materials are used in special circumstances; the material configuration of mechanical seal dynamic and static rings is more critical. It is not that cemented carbide is the best to cemented carbide. The high price is one thing, two It is not reasonable that there is no difference in hardness, so it is best to treat them differently according to the characteristics of the medium.
The choice of chemical pump under special medium
sulfuric acid
The corrosion of sulfuric acid with different concentrations and temperatures is quite different. For concentrated sulfuric acid with a concentration above 80% and temperature less than 80℃, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid.
Materials not suitable for use as pump valves:
Ordinary stainless steel such as 304 (0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti)
Pump valves for transporting sulfuric acid are usually made of high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (alloy 20). Fluoroplastics have better resistance to sulfuric acid, and fluorine-lined pumps (F46) are a more economical choice.
hydrochloric acid
Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and ferrosilicon containing molybdenum can only be used for hydrochloric acid below 50°C and 30%.
Contrary to metal materials, most non-metal materials have good corrosion resistance to hydrochloric acid, so rubber pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choices for transporting hydrochloric acid.
Nitric acid
Most 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 steels containing molybdenum (such as 316, 316L) ) The corrosion resistance to nitric acid is not only not better than ordinary stainless steel (such as 304, 321), and sometimes even worse. For high temperature nitric acid, titanium and titanium alloy materials are usually used.
acetic acid
It is one of the most corrosive substances in 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 is also suitable for high temperature and dilute acetic acid vapor. . For harsh requirements such as high temperature and high concentration of acetic acid or other corrosive media, high alloy stainless steel or fluoroplastic pumps can be used.
Alkali (sodium hydroxide)
The corrosion resistance of ordinary stainless steel to lye has no obvious advantages compared with cast iron. As long as a small amount of iron is allowed to be mixed in the medium, stainless steel is not recommended.
For high-temperature lye, titanium and titanium alloy or high-alloy stainless steel are mostly used. The company's general cast iron pumps can be used for low-concentration lye at room temperature, and various stainless steel pumps or fluoroplastic pumps can be used for special requirements.
Ammonia (Ammonia Hydroxide)
Most metals and non-metals have slight corrosion in liquid ammonia and ammonia (ammonia hydroxide). Only copper and copper alloys are not suitable for use.
Salt water (sea water)
The corrosion rate of ordinary steel in sodium chloride solution, sea water and salt water is not very high, and coating protection is generally required. Various types of stainless steel also have a very low uniform corrosion rate, but may cause localized corrosion due to chloride ions, usually 316 stainless steel is better.
Alcohols, ketones, esters, ethers
Common alcohol media include methanol, ethanol, ethylene glycol, propanol, etc., ketone media include acetone, butanone, etc., ester media include various methyl and ethyl esters, and ether media include methyl ether, ethyl ether, Butyl ether, etc., they are basically non-corrosive, and common materials can be applied. When selecting, a reasonable choice should be made 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, so errors should be avoided when selecting sealing materials.
Effect of viscosity temperature
The viscosity of the medium has a great influence on the performance of the pump. When the viscosity increases, the head curve of the pump decreases, and the head and flow of the best working conditions decrease, while the power increases accordingly, and the efficiency decreases. Generally, the parameters on the sample are the performance when transporting clean water, and should be converted when transporting viscous media (the correction coefficients for different viscosities can be found in the relevant conversion chart). For the transportation of high viscosity slurries, pastes and viscous liquids, screw pumps are recommended.
For media with a temperature lower than 120°C, no special cooling system is usually set up, and its own media is mostly used for lubrication and cooling.
For the medium above 120°C and within 300°C, a cooling chamber must be provided on the pump cover, and the sealed chamber should also be connected with coolant (double mechanical seal is required). When the coolant is not allowed to penetrate into the medium, After cooling the medium itself, it is connected (can be realized by a simple heat exchanger).
For the high temperature medium above 300℃, 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 center support. The mechanical seal is preferably metal bellows, but the price is high (the price is More than 10 times that of ordinary mechanical seals).
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Wuxi Xinjiuyang Pumps does not yield to price pressure in terms of product quality. Although market competition is fierce, it will never reduce product quality. Three guarantees for product quality (repair, replacement, and return) are implemented for one year, and spare parts will be provided free of charge due to product quality problems (repair, replacement) within one year, and cost will be charged as appropriate after one year. Wuxi Xinjiuyang The pump company provides lifetime warranty and accessories. If we are unable to deal with the quality problem, we will refund within one year.
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1. The products produced by our company have reached strict corporate standards and the standards of the Ministry of Machinery.
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3. During the warranty period, if the product is indeed damaged or not working properly due to quality problems, our company is responsible for free repair or replacement, and provide relevant maintenance knowledge; if the damage is caused due to improper use by the user or outside the warranty period Damaged or abnormal work, the company provides lifetime maintenance services for the product. If the user needs, the company provides free consultation and on-site guidance for installation and commissioning.
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