CENTRIFUGES

Description

CA centrifuge can separate solid material and oil from liquid effluent. Centrifuges rotate rapidly and impose centrifugal forces of 500-5000 g on the materials to be separated greatly increasing the rate of solid separation. The rotation causes the most dense solids to migrate to the wall of the centrifuge and the least dense material (usually the liquid) to remain nearer to the centre. The separated materials are discharged independently.

In a decanter centrifuges, a horizontally or vertically mounted tube or bowl with a tapering end is rotated. A scroll rotates within the bowl at a slightly different speed. This action moves the solids to the end of the taper where they are discharged. The liquid flows over a circular weir that can be at either end of the centrifuge.

Disc centrifuges (see illustration on Oil separators technology page) are used mainly for the separation of oil from liquids and slurries. They consist of a stack of vertical cones 05-1 mm apart. The high surface area of the plates enhances the separation of oil droplets as the unit rotates. Both decanter and disc centrifuges can be used for two-phase separations, such as solids and water, and three-phase separations, such as oil, solids and water.

Centrifuges can operate continuously or in batches, and are compact and enclosed. Gastight centrifuges can be used to separate toxic, corrosive or flammable material.

Application

Centrifuges are used to dewater sludges and to thicken activated sludge for recycling. Centrifuges are also used in waste treatment and in recycling systems in breweries, oil refineries and the chemical, pharmaceutical, food and paper Industry. By reducing the water content of sludges, the cost of handling and disposal is reduced. Sewage sludge can generally be dewatered to 20-25% dry solids.

Centrifuges can handle feeds at a range of particle sizes. The finest particles can be flocculated before centrifugation. Centrifuges can operate continually, are insensitive to variations in feed and can handle sludges with high or low frictional qualities or other sticky materials.

Sizing

Centrifuges are available in a range from 4 - 200 kW and typically consume about 15 kWh per cubic metre of liquid treated. Centrifuges generally have low running costs and take up considerably less space than, for example, a filter press.