Centrifuges are sedimentation devices in which suspended solids are separated from a liquid under the action of centrifugal forces generated by spinning the internal bowl of the centrifuge.
The resulting settling velocities of the solids can be significantly higher than those generated by gravity forces.
Centrifuges can be thought of as sedimentation vessels operating under high “gravitational” forces.
Decanter centrifuges provide a highly versatile and reliable option for a large variety of separation processes. They are commonly used for the following applications:
- The separation of solid-liquid suspensions (two-phase separation),
- The separation of solid-liquid-liquid suspensions (three-phase separation),
- The thickening or dewatering of separated solids,
- The clarification of a liquid phase or liquid phases,
- The sizing of solids,
- The sorting of solids.
PROCESS FUNCTION OF CENTRIFUGE :-
Separation (solid/liquid, solid/liquid/liquid and solid/solid/liquid
Centrifugation can be used for solid-liquid separation provided the solids areheavier than the liquid. Centrifuge can also be used to separate a heavy phase,and two lighter liquid phases, with one of the lighter phases being lighter than theother. As discussed, solids can be lighter than liquid and separation is by flotationof the dispersed solid phase.
Clarification- minimal solids in liquid product
Centrifuge can be used to clarify the discharged separated lighter liquid phase.The objective is to minimize the discrete suspended solids in the light continuousphase. Usually, only fine submicron biosolids are left uncaptured by
centrifugation and they escape with the discharged light phase.
Classification -sort by size and density
Centrifuge is used to classify solids of different sizes. One of the several possible applications is to classify crystals of different size range, with the finer submicron sizes leaving with the light phase and retaining only the larger sizes in the separated heavy phase. Either of the separated solids can be the product. For example, the larger crystals can be the product crystals while the finer crystals are returned to the crystallizer to grow to larger crystals. Another similar application is to classify smaller size cell debris in the light liquid phase from the heavier
products after homogenizing cells.
Degritting- remove oversized and foreign particles
Degritting is similar to classification where unwanted particles, larger or denser, are rejected in the sediment, with product (smaller or less dense) overflowing in the lighter liquid phase. Another situation is where smaller unwanted particles are rejected in the light liquid phase, and valuable heavier solids are settled with the
Thickening or concentration- remove liquid, concentrate solids
Centrifuge is frequently used to concentrate the solid phase by sedimentation and compaction, removing the excess liquid phase in the overflow or centrate. This reduces the volume of the product in downstream processing.
Separation and repulping – remove impurities by washing or diluting
With a concentrated suspension containing contaminants such as salts and ions, it is diluted and washed so that the contaminants are dissolved in the wash liquid. Subsequently, the suspension is sent for centrifugation to remove the spent wash liquid with dissolved contaminants or finely suspended