How a Basket Centrifuge Works

A basket centrifuge separates solids from liquids much like a spin cycle in a washing machine, but at far higher speed and with a filter medium in place. The mixture is fed into a rotating cylindrical basket. Centrifugal force drives the liquid outward and through the basket, while the solids are held back and pile up against the wall as a filter cake.

The force involved is many times gravity, which pushes liquid through the cake and drains it far more completely than gravity draining ever could. This makes basket centrifuges good at producing a relatively dry cake and at recovering fine or high-value solid product.

There are two families of basket centrifuge, and they separate in different ways. A perforated (screen) basket has holes in its wall and is lined with a filter cloth or screen. Liquid passes through the cloth and out the perforations, and the solids stay behind as a cake. This is true filtration and is the most common basket type.

An imperforate basket has a solid wall and no perforations. It works by sedimentation, not filtration: denser solids settle against the solid wall and the clarified liquid forms an inner layer that overflows a lip or is skimmed off. Imperforate baskets are used when particles are too fine to filter, such as polishing a liquid to remove trace solids.

Most basket centrifuges run as batch machines. A charge of slurry is fed in and the basket spins up. Liquid filters through the cake while solids accumulate. When the cake reaches the design thickness, feed stops and the machine spins to dry the cake by driving out residual liquid.

If the product needs rinsing, a wash liquid is sprayed onto the cake and spun through, displacing mother liquor without redissolving the solids. After the dry-spin, the machine is unloaded. In a manual basket the operator stops the machine and digs the cake out; larger automated units slow down and use a plow or a scraper knife to peel the cake while still turning.

Because each cycle stops to load and unload, throughput is lower than a continuous machine, but the batch approach gives excellent control over cake washing and dryness, which is why basket centrifuges are common in fine chemical, pharmaceutical, and food processing.

The filter cloth or screen is a consumable and blinds (clogs) or tears over time, which shows up as slow filtration or solids bleeding into the filtrate. The basket itself can crack or corrode, and because it spins fast, a cracked basket is a serious safety concern that requires immediate inspection.

Bearings, the drive, the brake, and the seals all wear. Baskets must stay balanced, so uneven cake loading, corrosion, or a worn suspension can produce vibration. Repairs typically include recladding or replacing the basket, renewing bearings and cloth, and static and dynamic balancing followed by a test run before the machine returns to service.