Centrifugal machine is mainly used to separate solid particles in suspension liquid from liquid; Or separate two immiscible liquids with different densities in the emulsion (e.g. separating cream from milk); It can also be used to remove liquids from wet solids, such as drying wet clothes with a washing machine; The special overspeed tubular separator can also separate gas mixtures with different densities; Taking advantage of the different settling velocity of solid particles with different density or particle size in liquid, some settling centrifuges can also classify solid particles according to density or particle size.
Industrial centrifuges were invented in Europe. For example, in the mid-19th century, there were three-column centrifuges for textile dehydration and top-suspended centrifuges for separating crystalline granulated sugar in sugar factories. These earliest centrifuges were operated intermittently and discharged manually. Due to the improvement of slag unloading mechanism, continuous operation centrifuge equipment appeared in the 1930s, and intermittent operation centrifuge has also been developed due to the automatic control.
According to the structure and separation requirements, industrial centrifuges can be divided into filter centrifuges, sedimentation centrifuges and separators. A centrifuge has a cylinder called a drum rotating at high speed around its axis, which 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. Under the action of centrifugal force, each component is separated and discharged respectively. Generally, the higher the rotating speed of the drum, the better the separation effect.
The working principle of industrial centrifuge includes centrifugal filtration and centrifugal sedimentation. Centrifugal filtration is to make the centrifugal pressure generated by the suspension under the centrifugal force field act on the filter medium, making the liquid become filtrate through the filter medium, and the solid particles are intercepted on the surface of the filter medium, so as to realize liquid-solid separation; Centrifugal sedimentation is the principle of rapid sedimentation and stratification of components under centrifugal force field in different density of suspension (or emulsion) to realize liquid-solid (or liquid-liquid) separation. There is also a kind of separator for experimental analysis, which can carry out liquid clarification and solid particle enrichment, or liquid-liquid separation. This kind of separator has different operating structural types under atmospheric pressure, vacuum and freezing conditions.
The separation factor is an important index to measure the separation performance of centrifugal separator. It represents the ratio of the centrifugal force of the separated material in the drum to its gravity. The greater the separation factor is, the faster the separation is usually, and the better the separation effect is. The separation factor of industrial centrifugal separator is generally 100 ~ 20000, the separation factor of overspeed tubular separator can be as high as 62000, and the separation factor of overspeed separator for analysis can be as high as 610000. Another factor that determines the processing capacity of the centrifugal machine is the working area of the drum. The working area is large and the processing capacity is also large.
The selection of centrifugal machine shall be based on the comprehensive analysis of the size and concentration of solid particles in suspension (or emulsion), the density difference between solid and liquid (or two liquids), liquid viscosity, the characteristics of filter residue (or sediment) and the separation requirements as well as peeler centrifuge working principle, so as to meet the requirements for the moisture content of filter residue (sediment) and the clarity of filtrate (separation liquid). Then preliminarily select the type of centrifuge. Then the type and specification of centrifuge are determined according to the processing capacity and automation requirements for operation, and finally verified by actual test.
Generally, for suspensions containing particles with particle size greater than 0.01 mm, filter centrifuge equipment can be selected; For fine particles or compressible deformable particles in suspension, sedimentation centrifuge should be selected; When the suspension has low solid content, small particles and high requirements for liquid clarity, a separator shall be selected.