Historical development of the medical centrifuge
In ancient China, people tied the clay pot with one end of the rope, held the other end of the rope, rotated the pot, generated centrifugal force to squeeze out the honey in the pot, this was the early application of the principle of centrifugal separation.
Industrial centrifuges were born in Europe. For example, in the middle of the 19th century, three-foot centrifuges for textile dehydration and top-suspended centrifuges for separating crystalline sugar in sugar mills appeared successively. These earliest centrifuges were intermittent operation and manual slagging.
Due to the improvement of the unloading mechanism, continuous operation centrifuges appeared in the 1930s, and intermittent operation centrifuges were also developed due to the realization of automatic control.
Industrial centrifuges can be divided into filter centrifuges, sedimentation centrifuges and separators according to the structure and separation requirements.
The centrifuge has a cylinder that rotates around its axis at high speed, called a drum, and is usually driven by an electric motor. After the suspension (or emulsion) is added to the drum, it is quickly 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 effect.
The centrifugal separator has two functions: centrifugal filtration and centrifugal sedimentation. Centrifugal filtration is the centrifugal pressure generated by the suspension in the centrifugal force field, which acts on the filter medium, so that the liquid passes through the filter medium and becomes the filtrate, while the solid particles are trapped on the surface of the filter medium to achieve liquid-solid separation; centrifugal sedimentation is used The principle that the components of the suspension (or emulsion) with different densities settle rapidly in the centrifugal force field to achieve liquid-solid (or liquid-liquid) separation.
There is also a type of separator for experimental analysis, which can perform liquid clarification and solid particle enrichment, or liquid-liquid separation. This type of separator has different structural types that operate under normal pressure, vacuum, and freezing conditions.
An important indicator to measure the separation performance of a centrifuge is the separation factor. It represents the ratio of the centrifugal force to the gravity of the material to be separated in the drum. The larger the separation factor, the faster the separation and the better the separation effect. The separation factor of industrial centrifugal separators is generally 100 to 20000, the separation factor of ultra-velocity tube separators can be as high as 62,000, and the separation factor of ultra-velocity separators for analysis is as high as 610,000. Another factor that determines the processing capacity of the centrifugal separator is the working area of the drum. A large working area also has a large processing capacity.
Filter centrifuges and sedimentation centrifuges mainly rely on increasing the diameter of the drum to expand the working surface on the circumference of the drum; in addition to the circumferential wall of the drum, the separator also has additional working surfaces, such as the disc and chamber of the disc separator The inner cylinder of the separator significantly increases the settlement working surface.
In addition, the more detailed the separation of solid particles in the suspension, the more difficult it is, and the fine particles carried away in the filtrate or separated liquid will increase. In this case, the centrifuge needs a higher separation factor to effectively separate; When the liquid viscosity is high, the separation speed slows down; the density difference of each component of the suspension or emulsion is large, which is beneficial to centrifugal sedimentation, while the suspension centrifugal filtration does not require the density difference of each component.
The choice of centrifugal separator must be based on the size and concentration of the solid particles in the suspension (or emulsion), the density difference between the solid and the liquid (or two liquids), the viscosity of the liquid, the characteristics of the filter residue (or sediment), and the separation requirements A comprehensive analysis was carried out to meet the requirements for the moisture content of the filter residue (sediment) and the clarity of the filtrate (separation liquid), and which type of centrifugal separator was initially selected. Then according to the processing capacity and the automation requirements of the operation, the type and specifications of the centrifuge are determined, and finally verified by the actual test.
Generally, for suspensions containing particles greater than 0.01 mm in size, filter centrifuges can be used; for suspensions with small particles or compressible deformation, sedimentation centrifuges should be used; for suspensions with low solids content, small particles, and When liquid clarity is required, a separator should be used.
The future development trend of centrifugal separators will be to strengthen the separation performance, develop large-scale centrifugal separators, improve the slag discharge mechanism, increase special and combined drum centrifuges, strengthen the separation theory research and study the optimization control technology of the centrifugal separation process.
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