The principle and historical development of the centrifuge A centrifuge is a machine that uses centrifugal force to separate liquid and solid particles or components of a mixture of liquid and liquid. The centrifuge is mainly used to separate the solid particles in the suspension from the liquid, or separate the two liquids of different density and incompatible liquid in the emulsion (for example, separating the cream from the milk); it can also be used to exclude Liquid in wet solids, such as wet clothes in a washing machine; special ultra-speed tubular separators can also separate gas mixtures of different densities; use different density or granularity of solid particles to set different velocity in liquid, some sedimentation Centrifuges can also classify solid particles by density or particle size. A centrifuge is a machine that uses centrifugal force to separate liquid and solid particles or components of a mixture of liquid and liquid. The centrifuge is mainly used to separate the solid particles in the suspension from the liquid; or to separate the two liquids of different density and immiscible in the emulsion (for example, separating the cream from the milk); it can also be used to exclude Liquid in wet solids, such as wet clothes in a washing machine; special ultra-speed tubular separators can also separate gas mixtures of different densities; use different density or granularity of solid particles to set different velocity in liquid, some sedimentation Centrifuges can also classify solid particles by density or particle size. Centrifuges are widely used in chemical, petroleum, food, pharmaceutical, mineral processing, coal, water treatment and shipbuilding sectors. In ancient China, people used one end of a rope to hold a clay pot, and held the other end of the rope, rotating the pottery jar, and generating centrifugal force to squeeze out the honey in the pot. This is the early application of the centrifugal separation principle. Industrial centrifuges were born in Europe. For example, in the middle of the 19th century, there were three-legged centrifuges for textile dehydration and top-suspension centrifuges for separating crystal sugar from sugar factories. These earliest centrifuges were batch operated and manually drained. Due to the improvement of the slag discharge mechanism, a continuously operating centrifuge appeared in the 1930s, and the intermittent operation of the centrifuge was also developed due to the realization of automatic control. Industrial centrifuges can be divided into three types: filtration centrifuge, sedimentation centrifuge and separator according to structure and separation requirements. The centrifuge has a cylinder that rotates at a high speed about its own axis, called a drum, which is usually driven by an electric motor. After the suspension (or emulsion) is added to the drum, it is rapidly driven to rotate at the same speed as the drum, and the components are separated under the action of centrifugal force and discharged separately. Generally, the higher the drum speed, the better the separation. The centrifugal separator has two working principles: centrifugal filtration and centrifugal sedimentation. Centrifugal filtration is the centrifugal pressure generated by the suspension under the centrifugal force field, acting on the filter medium, causing the liquid to pass through the filter medium to become the filtrate, and the solid particles are trapped on the surface of the filter medium to achieve liquid-solid separation; centrifugal sedimentation is utilized The principle of rapid sedimentation and stratification of the components with different densities (or emulsions) in the centrifugal force field enables liquid-solid (or liquid-liquid) separation. There is also a type of separator for experimental analysis that can perform liquid clarification and solid particle enrichment, or liquid-liquid separation. These separators have different structural types operating under atmospheric pressure, vacuum, and freezing conditions. An important indicator for measuring the separation performance of a centrifuge is the separation factor. It represents the ratio of the centrifugal force to the gravity of the separated material in the drum. The larger the separation factor, the faster the separation is usually and the better the separation effect. The separation factor of the industrial centrifugal separator is generally 100 to 20000, the separation factor of the super-speed tubular separator can be as high as 62000, and the separation factor of the analytical super-speed separator is up to 610000. Another factor that determines the processing capacity of the centrifuge is the working area of ​​the drum, which is also large in processing area. The centrifuge should be selected according to the size and concentration of solid particles in the suspension (or emulsion), the density difference between solid and liquid (or two liquids), the viscosity of the liquid, the characteristics of the filter residue (or sediment), and the requirements for separation. A comprehensive analysis was carried out to meet the requirements for the moisture content of the filter residue (sludge) and the clarity of the filtrate (separation liquid), and which type of centrifugal separator was initially selected. Then according to the amount of processing and the automation requirements for the operation, determine the type and specifications of the centrifuge, and finally verify by the actual test. Generally, for suspensions containing particles larger than 0.01 mm in size, a filter centrifuge can be used; for fine or compressible deformation of the suspension, a sedimentation centrifuge should be used; for the suspension, the solid content is low, the particles are small and When the liquid clarity is high, a separator should be used. Folding centrifuge price Centrifuge price The difference between the domestic centrifuge and the imported centrifuge is not very large. At present, the core technology of the centrifuge has been supported in China. The price difference between centrifuges of the same grade is not very large, mainly in terms of performance and configuration. The difference between the mainframes is that in terms of performance, centrifuges with refrigeration are much more expensive than ordinary ones, and some centrifuges also have heating functions. The more the order, the higher the price of the centrifuge. The big difference is the configuration aspect, and sometimes the price of the attachment is often higher than the price of the host. When purchasing Note that in addition to the main unit, the selected rotor (quantity and type), plus the necessary centrifuge tubes, sleeves, special centrifuge bottles or blood bags, All of this adds up to the price of a complete centrifuge. Principle of centrifugation When the suspension containing fine particles is left stationary, the suspended particles gradually sink due to the action of the gravitational field. The heavier the particles, the faster the sinking, whereas the particles with a lower density than the liquid will float. The rate at which particles move under the gravitational field is related to the size, morphology, and density of the particles, and is related to the strength of the gravitational field and the viscosity of the liquid. Particles of the size of red blood cells, a few micrometers in diameter, can be observed under normal gravity. In addition, the substance is accompanied by a diffusion phenomenon when it settles in the medium. Diffusion is unconditional and absolute. The diffusion is inversely proportional to the mass of the material, and the smaller the particle, the more severe the diffusion. The settlement is relative, and if it is conditional, it must be subjected to external forces to move. The settlement is proportional to the weight of the object, and the larger the particle, the faster the sedimentation. For particles smaller than a few micrometers such as viruses or proteins, they are in a colloidal or semi-colloidal state in solution, and it is impossible to observe the sedimentation process by gravity alone. The smaller the particles, the slower the sedimentation, and the more severe the diffusion phenomenon. Therefore, it is necessary to use a centrifugal machine to generate a strong centrifugal force in order to force these particles to overcome the diffusion to produce a settling motion. Centrifugation is the use of the powerful centrifugal force generated by the high-speed rotation of the centrifuge rotor to accelerate the sedimentation velocity of the particles in the liquid, and separate the sedimentation coefficient and the buoyant density of the sample. History development In ancient China, people used one end of a rope to hold a clay pot, and held the other end of the rope, rotating the pottery jar, and generating centrifugal force to squeeze out the honey in the pot. This is the early application of the centrifugal separation principle. Industrial centrifuges were born in Europe. For example, in the middle of the 19th century, there were three-legged centrifuges for textile dehydration and top-suspension centrifuges for separating crystal sugar from sugar factories. These earliest centrifuges were batch operated and manually drained. Due to the improvement of the slag discharge mechanism, a continuously operating centrifuge appeared in the 1930s, and the intermittent operation of the centrifuge was also developed due to the realization of automatic control. Industrial centrifuges can be divided into three types: filtration centrifuge, sedimentation centrifuge and separator according to structure and separation requirements. The centrifuge has a cylinder that rotates at a high speed about its own axis, called a drum, which is usually driven by an electric motor. After the suspension (or emulsion) is added to the drum, it is rapidly driven to rotate at the same speed as the drum, and the components are separated under the action of centrifugal force and discharged separately. Generally, the higher the drum speed, the better the separation. The centrifugal separator has two working principles: centrifugal filtration and centrifugal sedimentation. Centrifugal filtration is the centrifugal pressure generated by the suspension under the centrifugal force field, acting on the filter medium, causing the liquid to pass through the filter medium to become the filtrate, and the solid particles are trapped on the surface of the filter medium to achieve liquid-solid separation; centrifugal sedimentation is utilized The principle of rapid sedimentation and stratification of the components with different densities (or emulsions) in the centrifugal force field enables liquid-solid (or liquid-liquid) separation. There is also a type of separator for experimental analysis that can perform liquid clarification and solid particle enrichment, or liquid-liquid separation. These separators have different structural types operating under atmospheric pressure, vacuum, and freezing conditions. An important indicator for measuring the separation performance of a centrifuge is the separation factor. It represents the ratio of the centrifugal force to the gravity of the separated material in the drum. The larger the separation factor, the faster the separation is usually and the better the separation effect. The separation factor of the industrial centrifugal separator is generally 100 to 20000, the separation factor of the super-speed tubular separator can be as high as 62000, and the separation factor of the analytical super-speed separator is up to 610000. Another factor that determines the processing capacity of the centrifuge is the working area of ​​the drum, which is also large in processing area. The filter centrifuge and the sedimentation centrifuge mainly rely on increasing the diameter of the drum to enlarge the working surface on the circumference of the drum; in addition to the circumferential wall of the drum, the separator has additional working surfaces, such as discs and chambers of the disc separator. The inner cylinder of the separator significantly increases the settlement working surface. In addition, the more difficult it is to separate the solid particles in the suspension, the fine particles carried away in the filtrate or the separation liquid will increase. In this case, the centrifugal separator needs a higher separation factor to effectively separate the suspension; When the viscosity of the liquid is large, the separation speed is slowed down; the difference in density of the components of the suspension or the emulsion is large, which is advantageous for centrifugal sedimentation, and the centrifugal filtration of the suspension does not require density difference of each component. The centrifuge should be selected according to the size and concentration of solid particles in the suspension (or emulsion), the difference in density between solid and liquid (or two liquids), the viscosity of the liquid, the characteristics of the filter residue (or sediment), and the requirements for separation. The comprehensive analysis is carried out to meet the requirements for the moisture content of the filter residue (sludge) and the clarity of the filtrate (separation liquid), and which type of centrifugal separator is initially selected. Then according to the amount of processing and the automation requirements for the operation, determine the type and specifications of the centrifuge, and finally verify by the actual test. Generally, for suspensions containing particles larger than 0.01 mm in size, a filter centrifuge can be used; for fine or compressible deformation of the suspension, a sedimentation centrifuge should be used; for the suspension, the solid content is low, the particles are small and When the liquid clarity is high, a separator should be used. The future development trend of centrifugal separators will be to strengthen separation performance, develop large centrifugal separators, improve slag discharge mechanism, increase dedicated and combined drum centrifuges, strengthen separation theory research and study centrifugal separation process optimization control technology. The enhanced separation performance includes increasing the rotation speed of the drum; adding a new driving force during the centrifugal separation process; speeding up the slag pushing speed; increasing the length of the rotating drum to prolong the time of centrifugal sedimentation separation. The development of large-scale centrifugal separators, mainly to increase the diameter of the drum and the use of double-sided drums to improve the processing capacity, so that the equipment investment, energy consumption and maintenance costs of processing unit volume of materials are reduced. In theoretical research, the main research is on the fluid flow condition and the formation mechanism of filter residue in the drum, and the calculation method of minimum resolution and processing capacity is studied. Daily maintenance Centrifuge drum Before the centrifuge is operated, the power should be cut off and the centrifuge brake should be loosened first. You can manually turn the drum to see if there is any bite. Check for other parts of the area for looseness and abnormality. Turn on the power and start the drive in a clockwise direction (usually about 40-60 seconds from standstill to normal operation). Usually, each equipment must be empty for about 3 hours after it arrives at the factory. It can work without abnormal conditions. Place the material as evenly as possible. Must be operated by a person, the capacity must not exceed the rated amount. Never overspeed the machine to avoid affecting the life of the machine. After the machine is started, if there is an abnormal situation, it must be stopped for inspection and repaired if necessary. The centrifuge is running at high speed, so it is not possible to touch the drum with the body to prevent accidents. The mesh size of the filter cloth should be determined according to the size of the solid phase particles of the separated material, otherwise the separation effect will be affected. In addition, the filter cloth should be installed with filter cloth. The sealing ring is embedded in the drum sealing groove to prevent the material from running in. In order to ensure the normal operation of the centrifuge, please rotate the parts every 6 months. At the same time, check the running lubrication condition of the bearing, whether there is wear phenomenon; whether the components in the brake device are worn or not, and replace it severely; the bearing cover has no oil leakage. After the machine is used, it should be cleaned and kept clean. Do not separate the non-preservative centrifuge from the highly corrosive materials; in addition, strictly follow the equipment requirements and regulations, non-explosion-proof centrifuges should not be used in flammable or explosive places. Folding centrifuge "surge" Centrifuges in refrigeration centrifugal units often experience "surge". The principle of a refrigerating centrifugal compressor is to compress a large molecular weight refrigerant by a high-speed movement to a small space for compression, and then condense by cooling. The energy adjustment mode of the centrifugal chiller is to adjust the compression ratio by adjusting the angle of the guide plate rotating at a high speed. When the cooling capacity is reduced, the work done by the guide vanes is lowered, and the pressure of the compressed gas is similar to the pressure of the gas sucked into the compressor, causing mechanical reversal of the gas backflow. (Also called "surge") Surge can cause damage to mechanical parts. Centrifuge Development Centrifuge is a device for separating samples. It is widely used in biomedicine, petrochemical, agricultural, food hygiene and other fields. It uses the difference in precipitation speed of different substances in the centrifugal force field to realize the analysis and separation of samples. Since the advent of the centrifuge, the progress of low speed, adjustment and overspeed has been mainly reflected in the centrifugal equipment and centrifugal technology, and the two complement each other. From the perspective of rotational speed, the desktop centrifuge is basically in the category of low-speed, high-speed centrifuges. Therefore, it has the technical characteristics of low-speed and high-speed centrifuges. Its structure is mainly composed of motor drive system, refrigeration system, mechanical system, rotor and system control. The composition is only a small size and capacity compared to the floor-standing centrifuge. The development of general-purpose desktop centrifuges has blurred the boundaries of low-speed, high-speed, micro- and large-capacity centrifuges. Numerous rotors provide researchers with a wide range of applications and become the preferred model for research laboratories, such as ST2l in Sorvall, USA. , Germany's Heraeus new model Biofuge Stratos and so on. How to choose There are many types and types of centrifuges, and the price is relatively expensive. When purchasing, it should be measured according to the work. Usually should consider the following factors: (1) The purpose of centrifugation, analysis of centrifugation or preparation of centrifugation; (2) The type and quantity of the sample, whether it is a cell, a virus, or a protein, the amount of the sample. Based on these factors, decide whether to purchase an analytical centrifuge or a centrifuge; whether it is low speed, high speed or overspeed; whether it is a large capacity, a constant or a small amount of centrifuge. (3) Economic ability: When the model is determined, the manufacturer and price should be considered, and the performance of the price and product is synchronized. (4) Other details: such as whether the centrifugal operation is simple, whether the maintenance is convenient, whether the design is outdated, and whether the wearing of the consumables is convenient. (5) Matching problem: It is impossible for a centrifuge to operate at low speed, high speed and over speed at the same time. Generally speaking, the ultracentrifuge is limited to ultracentrifugation. It is not suitable for high speed centrifugation and is not suitable for low speed centrifugation. The same high speed centrifuge is not suitable for low speed centrifugation. Therefore, if you want to buy a supercentrifuge, you should consider a high-speed centrifuge, otherwise you will not be able to play an advantage. Generally speaking, the use of low speed and high speed is relatively high, and the utilization rate of the ultracentrifuge is low. The ultracentrifuge is only used in the laboratory for frequent purchase or considering regional common settings. After the model of the centrifuge is determined, what kind of centrifugal rotor is purchased. The most important basis for consideration is the capacity of the sample and the conditions of centrifugation. Usually there is one horizontal rotor and one corner rotor, or one large capacity (relatively lower speed) rotor and one small capacity high speed rotor can meet different needs in the work. Because there are many types of centrifugal rotors, many are similar, and the speed of the overspeed machine is quite expensive. It is not necessary if the price is all several times higher than the centrifuge mainframe. Due to the different prices of the rotor speed, the price difference is very large. From the speed of rotation, it is not advisable to pursue the higher the better, but there should be a rotor with the highest speed allowed by the centrifuge, otherwise it is a waste for the centrifuge. Units with two centrifuges can be considered to save money by considering the complementary rotor models. Centrifuge management, from the use of centrifuges in many years in China, all types of centrifuges should be managed and maintained by special personnel. High and ultra-speed centrifuges require regular inspection and maintenance. Users should record the experimental status and maintenance conditions in detail to ensure the safe use of the centrifuge. High and low speed centrifuges can be used by themselves after reading the instructions and training the centrifuge operating procedures. The structure of the ultracentrifuge is complicated, the working procedure is also cumbersome, and the accident is easy to occur, and the centrifugal head should be carefully maintained and used. From the perspective of domestic use and management for many years, the storage and operation of special personnel is the guarantee that the instrument is in good condition. Management and operation personnel should be trained so that they are not only familiar with the operation, but also should understand the instrument. Explosion-proof special [1] Centrifuges are widely used in many fields of the national economy, such as chemical and pharmaceutical industries. They are still the main equipment for solid-liquid separation in the production process of chemical intermediates and pharmaceutical raw materials. Due to the different physical and chemical properties of the applications, processes and media used in centrifuges in these industries, there are different requirements for centrifuges, such as material requirements, structural requirements, anti-corrosion requirements, and explosion-proof requirements. The following linkage hardware introduces you to the design of a nitrogen protection explosion-proof system that combines the application of a digital oxygen meter with an effective safety and safety production of centrifuges in chemical and pharmaceutical industries. Explosion protection requirements We know that the three elements that generate explosions are temperature, fire source, oxygen, and the simultaneous existence of three basic conditions to prevent chemical explosion. It is the basic theory for preventing chemical explosion of combustible materials. In other words, the essence of all technical measures to prevent chemical explosion of combustible materials is to prevent the simultaneous existence of three basic conditions of chemical explosion. among them: (1) Temperature, for a specific medium, whether it is liquid phase or gas phase, the operating temperature of the centrifuge should be considered in the process design, which depends mainly on the process conditions, and will not be elaborated here; (2) Fire source, in the design of the centrifuge, apply enough safety air-rotor pump room to the moving parts to eliminate possible mechanical friction and impact. At the same time, the machine must have measures to eliminate static electricity. For brake devices, mechanical friction brakes should not be used, generally in the form of electrical energy brakes (non-contact brakes, the disadvantage is that the brake time is longer than the contact type, especially when fully loaded) This is especially true in cases where the inertia is large.) In addition, for the drive belt, an anti-static belt is used to eliminate or reduce the possibility of static electricity generation; (3) Oxygen is generally protected by an inert gas. The inside of the centrifuge is filled with nitrogen to replace the air inside, so that the oxygen concentration is maintained within a safe range. Explosion-proof measures At present, the commonly used centrifuge nitrogen protection is actually only a nitrogen inlet pipe and a nitrogen gas outlet pipe are arranged on the casing. When the centrifuge is working, the inner cavity is filled with nitrogen. As to whether the nitrogen concentration can reach the safe range, there is no quantitative control, and therefore, the reliability of the nitrogen protection is poor. An improved nitrogen protection system is designed with an online oxygen detection device and a pressure transmission sensor to detect the oxygen concentration in the centrifuge chamber during operation, and to perform quantitative control to control the oxygen content within a safe range (also That is to say, the oxygen concentration in the machine is outside the explosion limit of the flammable and explosive medium). 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