ISPE Glossary of Pharmaceutical and Biotechnology Terminology

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Centrifuge

A device in which solid or liquid particles of different densities are separated by rotating them in a tube in a horizontal circle. The denser particles tend to move along the length of the tube to a greater radius of rotation, displacing the lighter particles to the other end.

Publication Source: Food and Agricultural Organization of the United Nations (FAO)
Publication Date: 1999

Centrifuge

A centrifuge operates on the principle of centrifugal force, the inertial reaction by which a body tends to move away from a center about which it revolves. This technique is commonly used to separate solids from liquids or liquids of different densities. Centrifugal equipment is divided into two major types, sedimenters and filters:

Sedimenters

For sedimentation, batch and continuous centrifuges are available. There are three types of centrifuges for continuous sedimentation.

a) Disc – constructed on the vertical axis, disc centrifuges are solid-bowl units. All are capable of separating liquids from solids, solids from two immiscible liquids and two immiscible liquids. Disc-stack centrifuges differ in their ability to handle different volumes of solids in the feed stream, and in the way that the separated solids are removed from the separation vessel: solids-retaining, solids-ejecting, and nozzle-bowl separators.

b) Decanters – consists of a cylindrical settling section with a tapered end. Inside the bowl is a scroll conveyor that is driven usually at a slightly faster rate than the bowl and can be controlled by a differential speed device or back drive.

c) Tubular – a vertical solid-wall cylinder provided with caps on both ends; a tubular centrifuge generally has a bottom feed inlet. When two liquids of different specific gravities are fed, the heavier phase is concentrated against the wall while the lighter phase “floats” on the heavier phase.

Filters

Filtering centrifuges accommodate a range of liquid-solid separations. The two batch types, basket and peeler centrifuges, can separate almost any liquid-solid slurry. For continuous operation, there are pusher and conical centrifuges.

a) Pusher – with a horizontal axis, the pusher centrifuge operates at a constant fixed speed. It has a perforated bowl, generally with a bar-type screen. One end of the bowl is open while the opposite end is closed with a reciprocating diaphragm, or disc, which rotates with the bowl.

b) Conical – the standard conical centrifuge consists of a cone with a small closed end and a large open end to which is attached a coarsely woven drainage screen, topped with a filter screen or perforated plate. A compartmentalized casing surrounds the bowl. There are two variations of the basic conical centrifuge: the tilting conical centrifuge and the conveyor conical type.

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