Lynne Wong's PhD thesis

In Mauritius, most of the sugar factories use lime saccharate, a mixture of milk of lime and
sucrose syrup, as this liming agent has been found more efficient than milk of lime alone
(Wong Sak Hoi and Chung, 1996). After liming, the juice is superheated to 103 – 105 °C
and allowed to flash to the constant boiling point at atmospheric pressure. This forces out
the air present in the juice and also causes bagacillo particles to burst and sink with the
solids. The flashed limed juice is then sent to decant in a large vessel called a clarifier
where the clear juice separates from the precipitated solids. Flocculation and settling are
aided by the addition of synthetic water soluble flocculants, which are partially hydrolysed
polyacrylamides. The clear juice is removed from the top and sent to evaporators while the
muds are pumped from the bottom of the clarifier to a rotary vacuum filter. The filtered
juice is sent back to process while the filter cake is returned to the fields as soil conditioner
or fertilizer.
The techniques used for clarification and filtration were comprehensively reviewed by
Whayman (1992).
1.2.5 Evaporation
The clear juice from the clarifier contains about 85% water. Two-thirds of this water is
evaporated in a vacuum multiple-effects evaporator consisting of a succession of vacuumboiling
vessels (usually 4 – 5) arranged in series or in parallel so that each succeeding body
has a higher vacuum, and therefore boils at a lower temperature. The vapours from one
body can thus boil the juice in the next one. With this arrangement, the exhaust steam
introduced into the first body of a quadruple-effect evaporator evaporates four times its
mass of water. The vapour from the final body of the evaporator goes to a barometric
condenser. The syrup leaving the evaporator contains about 65% refractometric solids
(Brix) and 35% water.
1.2.6 Crystallization
Crystallization takes place in single-effect vacuum pans, where the syrup is further
evaporated until saturated with sugar. "Seed grain" is then added to serve as nuclei for the
formation of sugar crystals, and more syrup is added as the water evaporates. Crystal
growth continues until the pan is full. For a skilled sugar boiler, the original crystals can
be grown without the formation of additional crystals (false grain), so that when the pan is
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