Centrifugation - White SugarBy Bento, Luis San Miguel
Posted on 2006-09-17 Last edited on 2010-12-17
The resulting massecuite from sugar crystallization is separated in its components, sugar crystals and mother syrup through centrifugation.
For high purity massecuites, as in white sugar, discontinuous high speed centrifuges are used.
In the beginning of centrifugation cycle, the basket rotate at a given velocity that allows centrigugal charge. At this speed, massecuite, comming from the masse distributor above the machines, flows into the basket and will be distributed evenly from the bottom to top of the basket. A mechanical sensor will indicates when the basket is full of massecuite. This sensor will actuate the feeding valve closing massecuite feeding. The centrifuge must be filled to its maximum capacity to optimize energy consumption. However, with special sugars, as with fine grain massecuites, the maximum capacity can not be reached, as the syrup purge of these massecuites is more difficult.
After charging, centrifugal basket speed up and syrup separation begins. It is important that syrup separation is made evenly and rapidly. If this does not happens it can means that basket screens are not cleaned or massecuite contains a great quantity of fine grain. Imediatly after syrup purge, sugar washing must start. This washing can be made with water and/or steam in one or two times. The wash combination and washing time depends on massuite grain size, colourants present and desired white sugar quality.
Water used in this operation must be clean condensate water at 95 oC (minimum). This water is injected through nozzles distributed vertically along the basket screen in such a a way that water jet will cover all the sugar from the top to the basket bottom.
After washing, centrifugal basket speed up till its maximum speed. This aceleration period must be enough to remove excess water/syrup between the crystals. Excess of speeding time can be dangerous if sugar become to dry. In this case dust and lumps will be formed during discharge. Speeding time must be enough to have a discharged sugar with around 1.5% of moisture.
After aceleration time, centrifige will slow down till the discharge velocity is reached. At this velocity, a blade will disloccate vertically, from top to bottom, removing all the sugar attached to the screen. It is important that, after this operation, the screen be as clean as possible. Any sugar maintained on the screen, after discharge, will be melted and the crystallization and centrifugation yield will decrease. This will increase steam and energy consumption.
After discharge, the screen is washed with hot water. The screen must be free of any sugar to facilitate the syrup purging in the next centrifugation cycle.
The syrup separated during massecuite centrifugation, refined syrup, is returned for next crystallization or is discharged to the Recovery section.
In some places continuous centrifugals are usde for white sugar centrifugation (as in Australia).
Market overview of sugar centrifugals, Zuckerindustrie, 132 (2007) Nr. 6, 471-
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