Sugar production
Step 2. Refined sugar production
A simplified process flow diagram from refined sugar production
is shown in figure. The raw sugar obtained from cane requires
refining to remove the molasses film and inorganic matter that
have not been removed during the clarification process. The
inorganic matter gives some color to the raw sugar that must
be eliminated to obtain white sugar. The refined sugar process
has several steps:
Affination
The first step in sugar refining is affination. This is a mechanical
process to remove the molasses film from raw sugar with warm,
almost saturated, syrup. Crystals are separated from the syrup
by centrifugal washing with hot water or a high purity solution
of sugar. The syrup from the crystal washing, called affination
syrup, is transferred to a remelt processing station and then
to the clarification step.
If the refinery is part of the raw sugar production facility,
the cane sugar may be washed more heavily in previous steps
and the affination step omitted.
Clarification
The main purpose of clarification is to eliminate the inorganic
impurities present in raw sugar. Chemical clarification, using
phosphatation and carbonation, is the preferred method, though
pressure filtration is also used.
The next step is decolorization, to remove soluble impurities
by adsorption by granular activate carbon and bone char, manufactured
from degreased cattle bones.
Evaporation
After clarification, the syrup must again be concentrated by
multiple-effect evaporators and crystallized by vacuum pans.
This is the same sequence used in the raw sugar process.
Multiple-effect evaporators are used to raise the syrup to 70
Brix before final concentration to the crystallization point
during the boiling process. In the multiple-effect process,
the syrup moves through several inter-connected vacuum vessels.
Every step (vessel) is called an effect.
Boiling step: The syrup is further concentrated by boiling until
sugar crystals are formed. Vacuum pans are used, requiring only
small changes in operating conditions. A final mix of white
sugar and residual molasses is obtained.
Crystallization step: Refined sugar crystallizers, as used in
raw sugar processing, cool the steam coming from the boilers
to facilitate separation of white sugar from the molasses. Separation
is carried out by centrifugation.
Drying and cooling
The damp sugar from the centrifuges is then treated in a special
piece of equipment usually consisting of 2 horizontal drums.
In the first drum, the sugar is dried by hot air and in the
second, known as the cooler, sugar crystals are dried in an
ambient temperature.
The sugar emerges from this stage with
a water content of 0.03 percent and a temperature of between
43-54 degree Celsius .
Screening
The sugar from the dryer-cooler passes over vibrating screens,
which separate out lumps that form when the sugar is sent
to the bagging hopper.
Packaging
The dried, cooled sugar is packed in 50 kilogram paper bags,
stitched with cotton thread, and labeled as white, refined,
sugar.
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