Sugar Production from Sugar Cane
Practical Action
Boiling
The boiling operation uses cascade type furnaces of various configurations. The massecuite is
removed from the final boiling pan at about 84ºBrix, at a temperature of around 112ºC.
Crystallisation
The massecuite is placed in U-shaped vessels where it is slowly rotated and allowed to cool for
up to 48 hours. This technique is often referred to as crystallisation in motion. Rotation
promotes even cooling of the massecuite which helps to achieve uniform crystal growth.
Seeding can also be carried out: that is granulated massecuite from a crystalliser in which grains
have already been developed are placed into the crystalliser before it is filled with fresh
massecuite. This helps to promote uniform crystal growth. The massecuite, now consisting of
crystals suspended in molasses, is transferred to the centrifuge.
Centrifuging
The centrifuge, a scaled-down version of those used in large-scale factories, consists of a
perforated inner drum located inside a larger drum. The perforated drum is rotated rapidly,
forcing the molasses to separate from the crystals. Water is sprayed into the spinning drum to
assist in the removal of the molasses.
The crystals of sugar are then removed from the centrifuge and transferred for drying. The
molasses are collected and can be reboiled, crystallised and re-centrifuged to produce a second,
lower quality, crystal sugar know as number two or B-sugar.
Drying and packaging
The crystals can be dried in a number of ways: by placing them in the sun, or by using simple
solar driers, or rotary or hopper driers which require fuel to provide drying heat. The dried
product can then be packed into suitable containers or bags for distribution.
Mini vacuum pan (VP) sugar processing
This is a scaled down version of large-scale sugar processing technology common throughout the
world. It is a high-cost, low-labour process suited to processing upward of 500 tonnes of sugar
cane per day with recovery rates of between 10 and 12%.
Extraction
The cane is first shredded then crushed using hydraulically loaded 3, 4 or 5-mill tandems. The
major difference between this and OPS roll mills is that water is sprayed onto the bagasse before
the final mill and diluted juice is recirculated to the previous mills. This system, known as
imbibition, helps to wash out more of the sucrose with the juice. Typically, extraction rates of
75% of the available juice are common.
Clarification
Clarification is carried out by lime sulphitation similar to that used in OPS, but here it is a
continuous rather than a batch process.
Evaporation
The major difference between the VP and OPS technology is the method of evaporating or boiling
the juice. Instead of in open pans the juice is boiled under vacuum, to about 70º Brix, inside
closed vessels or 'effects'. Low pressure steam is used to boil the juice which circulates through
tubes within a closed vessel. The vapour driven off passes into a second similar vessel, where it
is used to heat more juice. In order to maintain suitable temperature differentials for heat
transfer to occur, a partial vacuum is applied to each vessel, effectively lowering the boiling
temperature of the juice.
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