Types of Separation

One approach to classify centrifugal separations is according to the phase of the medium and the phase of the material to be purified, e.g. gas-gas, liquid-liquid or liquid-solid. Centrifugal separations of gas-phase materials are conducted in continuous mode only, while liquid-liquid and liquid-solid may be conducted in batch, semi-batch, or continuous modes. Gas-phase separations are very important in certain applications, particularly uranium isotope enrichment, but are highly specialized and not widely used. For space considerations, gas-phase separations are omitted from this discussion. Likewise, while liquid-liquid and even liquid-liquid-solid separations are common, discussion of the separation of immiscible liquids is, for the most part, limited to the discussion of centrifuge types in subsequent sections. Suffice it to say that the principles and approaches discussed in relation to liquid-solid separations generally apply to liquid-liquid separations. That is, small droplets of a liquid dispersed in a second, immiscible liquid will behave like solid particles settling through a liquid medium until the droplets sediment and coalesce, after which the methods to remove the separated liquids from the centrifuge usually differ from those used for solids removal.

Centrifugal separations may also be classified according to the method by which purified fractions are recovered. Three modes are used: (1) batch mode, in which the total sample to be separated is processed and then recovered at the conclusion of the run by decanting the supernatant and scraping the pellet from the rotor wall; (2) semi-batch mode, in which the sample mix is continuously fed to a spinning rotor as the supernatant is continuously discharged and the pellet is permitted to accumulate for post-run removal; and (3) continuous mode, in which the sample mixture is fed continuously, the supernatant is continuously discharged, and denser liquid or solid materials are either intermittently or continuously discharged while the run is in progress.

The types of separation to be discussed focus on the separation of solids from liquid media using any of the recovery modes described above. Discussion of simpler batch-mode operation is emphasized for simplicity. Three primary types of centrifugal separations are discussed: differential sedimentation, density gradient and filtration, with density gradient being further divided into rate-zonal and isopycnic (in isopycnic separations, particles sediment until they attain a position in the gradient at which the medium density is equal to their own).

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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