Cassava roots are firstly delivered to a sand removal drum and
then to a rinsing gutter for cleansing and peel separation. After
washing, the clean cassava roots are sent to a chopper to chop into
small pieces (approximately 20–25 mm) and then taken to a rasper.
During rasping, water is added to facilitate the process. The
resulting slurry, consisting of starch, water, fiber, and impurities, is
then pumped into the centrifuges for extraction of the starch from
the fibrous residue (cellulose). The extraction system consists of
three or four centrifuges in series. There are two types of extractors:
a coarse extractor with a perforated basket and a fine extractor with
a filter cloth. Suitable amount of water and sulfur-containing water
are constantly applied to the centrifuges for dilution and bleaching
of the starch. The starch slurry is then separated into starch milk and
fibrous residue. The coarse and fine pulp is passed to a pulp extractor
to recover the remaining starch and the extracted pulp is
then delivered to a screw press for dewatering. The dewatered fibrous
residue is sold to a feedstock mill. The starch milk from the
fine extractor is pumped into a two-stage separator for impurity
removal from the protein. After passing to a second dewatering
machine, the starch milk has the starch content up to 18–20
Baume´ . Then, the concentrated starch milk is pumped into dehydration
horizontal centrifuges (DHC) to remove water before
drying. The DHC consists of filter cloth placed inside, rotating at
about 1000 rpm to removewater from the starch milk. The resulting
starch cake has a moisture content of 35–40%. The starch cake is
taken to a drying oven consisting of a firing tunnel and drier stack.
Drying is effected by hot air produced by oil burners. During the
drying process, the starch is blown from the bottom to the top of the
drier stack and then fallen into a series of two cyclones in order to
cool down the starch. The dried starch with a moisture content of
less than 12% is conveyed through a sifter for size separation and
finally packaging.