Centrifuge is the use of centrifugal force, separation of liquid and solid particles or liquid and liquid mixture of the components of the mechanical. The centrifuge is mainly used to separate the solid particles from the liquid from the liquid; or to separate the two different densities and incompatible liquids in the emulsion (for example, to separate the cream from the milk); it can also be used to exclude Wet solids in the liquid, such as washing clothes with wet clothes; special ultra-speed tube separator can also be separated from different density of gas mixture; the use of different density or particle size of solid particles in the liquid settling speed of different characteristics, some settlement The centrifuge can also classify the solid particles by density or particle size.
In ancient China, people tied one end of the rope with the end of the rope, holding the other end of the rope, rotating the pot, and 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, such as the mid-19th century, there have been three-foot textile dehydration centrifuge, and the sugar factory separation of crystalline sugar with the hanging centrifuge. These first centrifuges are intermittent and manual slag.
As a result of the improvement of the slagging mechanism, the continuous operation of the centrifuge in the 1930s, intermittent operation of the centrifuge is also achieved by the automatic control and development.
Industrial centrifuge according to the structure and separation requirements, can be divided into filter centrifuge, sedimentation centrifuge and separator three categories.
The centrifuge has a cylinder that rotates about its own axis at high speed, called a drum, usually driven by a motor. Suspension (or emulsion) after adding the drum, was quickly driven with the drum at the same speed rotation, under the action of centrifugal force components separated, and were discharged. Usually, the higher the drum speed, the better the separation effect.
Centrifugal separator principle of the role of centrifugal filtration and centrifugal sedimentation two. Centrifugal filtration is the centrifugal pressure generated by the suspension in the centrifugal force field, acting on the filter medium, passing the liquid through the filter medium into the filtrate, and the solid particles are trapped on the surface of the filter medium to achieve liquid-solid separation; centrifugal sedimentation Suspension (or emulsion) density of the different components in the centrifugal force field quickly settling the principle of separation, to achieve liquid - solid (or liquid - liquid) separation.
There are also a class of analytical separators for liquid clarification and solid particle enrichment, or liquid-liquid separation. These separators have different structural types of operation under normal pressure, vacuum and freezing conditions.
An important indicator of the separation performance of centrifugal separators is the separation factor. It indicates that the separation of the material in the drum by the centrifugal force and its gravity ratio, the greater the separation factor, usually the more rapid separation, the better the separation effect. Industrial centrifugal separator separation factor is generally 100 ~ 20000, ultra-speed tube separator separation factor can be as high as 62000, analysis of ultra-speed separator separation factor up to 610000. Another factor that determines the handling capacity of the centrifuge is the working area of the drum, and the working area is also large in handling capacity.
Filter centrifuge and sedimentation centrifuge, mainly rely on to increase the drum diameter to expand the drum circumference on the face; separator in addition to drum peripheral wall, there are additional work surface, such as disc separator disc and room The inner cylinder of the separator significantly increases the settlement face.
In addition, the more difficult the separation of the solid particles in the suspension, the more difficult to remove the fine particles in the filtrate or separation solution. In this case, the centrifugal separator requires a higher separation factor to be effectively separated; When the viscosity of the liquid is large, the separation rate slows down; the density difference of the components of the suspension or the emulsion is large, which is favorable for the centrifugal sedimentation, and the centrifugal filtration of the suspension does not require the density difference of the components.
The choice of centrifugal separator shall be based on the size and concentration of solid particles in the suspension (or emulsion), the density difference between the solid and the liquid (or both liquids), the viscosity of the liquid, the characteristics of the residue (or sediment), and the separation requirements And so on a comprehensive analysis to meet the residue (sediment) moisture content and filtrate (separation liquid) clarity requirements, the initial choice of which type of centrifugal separator. And then according to the amount of processing and operation of the automation requirements to determine the type and specifications of the centrifuge, and finally verified by the actual test.
In general, a filter centrifuge may be used for suspensions containing particles larger than 0.01 mm in size; for sediment small particles or compressible and deformable, a settling centrifuge is preferred; for suspensions containing low solids, small particles and Liquid clarity requirements are high, should use the separation machine.
The future development trend of centrifugal separators will be to enhance the separation performance, the development of large-scale centrifugal separator, improve the slagging mechanism, increase the dedicated and combined drum centrifuge, strengthen the separation theory research and study the centrifugal separation process optimization control technology.
Strengthen the separation performance, including to improve the drum speed; in the centrifugal separation process to add a new impetus; speed up the slag speed; increase the length of the drum to centrifugal sedimentation separation time and so on. The development of large-scale centrifugal separator, mainly to increase the drum diameter and the use of double-sided drum to improve the processing capacity of the unit volume of equipment to invest in equipment, energy consumption and maintenance costs reduced. Theoretical research, the main study of the drum fluid flow and the formation mechanism of residue, the study of the minimum separation and processing capacity of the calculation method
When the suspension containing fine particles is stationary, the suspended particles gradually sink due to the action of the gravitational field. The heavier the particles, the faster the sink, and the smaller the density of the particles than the liquid will float. The velocity of the particles moving under the gravitational field is related to the size, morphology and density of the particles, and is related to the strength of the gravity field and the viscosity of the liquid. Like the size of red blood cells, the diameter of a few microns, you can observe the normal gravity of their settlement process.
In addition, the material in the medium when the sedimentation is accompanied by a diffusion phenomenon. Diffusion is unconditional absolute. Diffusion is inversely proportional to the quality of matter, and the smaller the particle, the more severe the diffusion is. While the settlement is relative, conditional, to be external force to exercise. Settlement is proportional to the weight of the object, and the larger the settling of the particles. For particles smaller than a few microns such as viruses or proteins, they are colloidal or semi-colloidal in solution, and it is impossible to observe the sedimentation process by gravity alone. Because the smaller the sediment the slower the particles, and the more serious the diffusion phenomenon. So the need to use a centrifuge to produce a strong centrifugal force in order to force these particles to overcome the proliferation of sedimentation movement.
Centrifugation is the use of centrifugal rotor high-speed rotation of the powerful centrifugal force generated to speed up the settling of the liquid particles in the sample, the different sedimentation coefficient and buoyancy density of the