What are the working principles of sedimentation centrifuges?

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The drum wall of a sedimentation centrifuge has no pores; under the action of centrifugal force, the phases in the mixture separate into layers based on their density or particle size. Those with higher density or particle size accumulate on the drum wall, while those with lower density or particle size accumulate in the center, thereby achieving the separation of the materials. The suspension added to the drum forms a ring-shaped liquid layer under the effect of centrifugal force; the solid particles in this layer settle onto the wall of the drum, forming sediment. The clarified liquid is discharged through the drum overflow port or suction pipe, and is known as the separated liquid. At the end of the separation, the sediment is removed by manual or mechanical means. As the solid particles settle toward the drum wall, they also move axially along with the liquid flow. When the feed rate is too high, these particles flow to the overflow port along with the liquid, while the finer particles that have not yet settled against the drum wall are discharged from the drum along with the separated liquid, causing the separated liquid to become turbid. For difficult-to-separate suspensions with a small density difference between the solid and liquid phases, small solid particles, or high liquid viscosity, a sedimentation centrifuge with a high separation factor should be used. Extending the time that the suspension stays in the drum is necessary to ensure that the separated liquid is clear – this can be achieved by reducing the feed rate or using a drum of larger length. Settling centrifuges have a wide range of applications; they are particularly suitable for the separation of suspensions in centrifugal filtration processes where excessive filtering resistance occurs due to solid particles clogging the filtering medium, or where too many fine particles escape. However, the moisture content of the sediment is relatively high. Settling centrifuges can be used for the separation of suspensions such as crystals, chemical precipitates, and coal powder, for the dewatering of various sewage sludges, and for removing impurities and clarifying animal and vegetable oils