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 incompatible liquid in the emulsion (for example, separating the cream from the milk); it can also be used for elimination. Liquids in wet solids, such as wet clothes in washing machines; 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 The centrifuge 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, so that the liquid passes 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 normal 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 superspeed separator is up to 610000. Another factor that determines the processing capacity of the centrifuge is the working area of ​​the drum, which has a large processing capacity.
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. 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.
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