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Centrifugal Screens for Starch Extraction and Refining

Centrifugal screens and hydrocyclones are good partners in starch production. Hydrocyclones using gravity and screens using size in starch separation. A magnificent process brings them to work making high quality starch for a demanding international market.

Centrifugal screens are used for extracting tuber and root starches. Starchy tubers and roots are finely grated. Rotating rasper drums are used for the grating. The resulting rasping is pumped direct into the center of a rotating conical sieve, while we all the time flush with water or juice from a set of conical arranged sprays. The fibrous parts of the rasping is sliding off the rotating cone and dumps from the front edge of the cone. The starch is flushed through the screen onto the back of the cone and leaves the extractor as a crude starch slurry. The fibrous part - the pulp - is extracted more times in order to maximize starch yield. A counter current process allows extraction with a minimum of liquid and today we have no need for water in the extraction but use the juice from the raw materials themselves.

Today we also apply larger screens. Some with a diameter of one meter and a throughput of rasping from as much as 50 tones of potatoes or 30 tones of cassava per hour. Picture right show an extraction section for 3.500 tones of fresh raw material per day with three units in parallel.

The sieve itself is made in stainless steel and the precision perforation is made by a photographic technique making holes only 115 microns across. Screens are made of thin replaceable sieve plate placed on a stronger supporting frame or as thicker long-life self-supporting sieve plates.

The pulp leaves the extractor as a wet pulp - fine for cattle feeding. The crude starch slurry is passed on to hydrocyclones and more screens for refining.