Perforated Basket Centrifuge

Principle

• It is a filtration centrifuge. The separation is through a perforated wall based on the difference in the densities of solid and liquid phases

• The bowl contains a perforated side wall

• The liquid phase passes through the perforated wall, while solid phase is retained in the bowl

• The solid is removed after cutting the sediment by a blade after stopping the centrifuge

Construction

It consists of a stainless steel perforated basket (typically 1-2 m in diameter) lined with a filter cloth

The basket rotates at a speed which is typically < 25 s-1, higher speeds tending to stress the basket excessively

The product enters centrally and is thrown outwards by centrifugal force and held against the filter cloth

The filtrate is forced through the cloth and removed via the liquid outlet; the solid material is retained on the cloth

The cake can be washed if required by spraying water into the centrifuge

Working

• The material is kept on a basket when the basket is stationary

• The amount of material should be optimum, otherwise, during Centrifugation it puts a great strain on the basket. The loading of material done to give even distribution

• Power is applied to rotate the basket and maximum speed must be attained quickly

• The basket runs at 1000 revolutions per minutes

• The power require for running is small compared to the power require for starting and bringing it to the full speed

• During Centrifugation, the liquid passes through the perforated wall, while the solid phase retains in the basket • The liquid leaves the basket and is collected at the outlet

• The cake is then spun to dry as much as possible

• Sometimes higher speeds are used so that the cake will be completely dried

• After a definite period of time, the power is turned off. By applying a brake the Centrifuge is stopped

• The basket is brought to rest

• The solid cake is cut using a blade and then unloaded manually

Uses

1. Perforated basket Centrifuge is extensively used for separating crystalline drugs (such as aspirin) from the mother liquor is removed completely

2. It is also used for removing unwanted solids from a liquid. For example, precipitated proteins are removed from insulin

3. Sugar crystals are separated using perforated basket centrifuge

Advantages

1. The Centrifuge is very compact and it occupies very little floor space

2. It can handle slurries with a high proportion of solid and even those having paste like consistency

3. The final product has a very low moisture content

4. In this method, the dissolved solids are separated from the cake

5. The process is rapid

Disadvantages

1. The entire cycle is complicated resulting in considerable labour costs

2. It is a batch process

3. If the machine is adapted for prolonged operation, there is considerable were and tear of the equipment. On prolonged operation, the solids may from hard cake, due to the centrifugal force, which is difficult to remove simultaneously.