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Sugar - The Refining Process
The initial stage involves sampling, weighing and washing the sugarcane.
From there the material passes to can crushers and then into the mill. The
bagasse, which
results from the milling, is used in the boilers for steam production that is used to
power the process. The surplus bagasse from this stage is used in industry.
Juice obtained from the mill is weighed in order to continue with the heating, clarifying
and filtering process whereby those materials found in the juice, different to sucrose,
are separated. Once the juice evaporates concentrated cane syrup is obtained which is
taken to pans, where crystallization takes place. Subsequently the cooked mass is
obtained, that then goes to a centrifuge, where the sugar is separated from the syrup.
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Finally, the sugar is dried, cooled and packaged in its different forms, ready for
sale.
A slightly more detailed explanation follows for those interested.
Sugar Refining
Affination
The first stage of processing the raw sugar is to soften and then remove the layer of
mother liquor surrounding the crystals with a process called "affination". The
raw sugar is mixed with a warm, concentrated syrup of slightly higher purity than the
syrup layer so that it will not dissolve the crystals. The resulting magma is centrifuged
to separate the crystals from the syrup thus removing the greater part of the impurities
from the input sugar and leaving the crystals ready for dissolving before further
treatment.
The liquor which results from dissolving the washed crystals still contains some
colour,
fine particles, gums and resins and other non-sugars.
Carbonatation
The first stage of processing the liquor is aimed at removing the solids which make the
liquor turbid. Coincidentally some of the colour is removed too. One of the two common
processing techniques is known as carbonatation where small clumps of chalk are grown in
the juice. The clumps, as they form, collect a lot of the non-sugars so that by filtering
out the chalk one also takes out the non-sugars. Once this is done, the sugar liquor is
now ready for decolourisation. The other technique, phosphatation, is chemically similar
but uses phosphate rather than carbonate formation.
Decolourisation
There are also two common methods of colour removal in refineries, both relying on
absorption techniques with the liquor being pumped through columns of medium. One option
open to the refiner is to use granular activated carbon [GAC] which removes most colour
but little else. The carbon is regenerated in a hot kiln where the colour is burnt off
from the carbon. The other option is to use an ion exchange resin which removes less
colour than GAC but also removes some of the inorganics present. The resin is regenerated
chemically which gives rise to large quantities of unpleasant liquid effluents.
The clear, lightly coloured liquor is now ready for crystallisation except that it is a
little too dilute for optimum energy consumption in the refinery. It is therefore
evaporated prior to going to the crystallisation pan. |
Boiling
In the pan even more water is boiled off until conditions are right for sugar crystals to
grow. You may have done something like this at school but probably not with sugar because
it is difficult to get the crystals to grow well. In the factory the workers throw in some
sugar dust to initiate crystal formation. Once the crystals have grown the resulting
mixture of crystals and mother liquor is spun in centrifuges to separate the two, rather
like washing is spin dried. The crystals are then given a final dry with hot air before
being packed and/or stored ready for despatch.
Recovery
The liquor left over from the preparation of white sugar and the washings from the
affination stage both contain sugar which it is economic to recover. They are therefore
sent to the recovery house which operates rather like a raw sugar factory, aiming to make
a sugar with a quality comparable to the washed raws after the affination stage. As with
the other sugar processes, one cannot get all of the sugar out of the liquor and therefore
there is a sweet by-product made: refiners' molasses. This is usually turned into a cattle
food or is sent to a distillery where alcohol is made.
Product: White Refined Cane Sugar (Grade A)
Specification:
Polarization - 99.8 Min A
Ash Content - 0.04% Max
Radiation - Normal
Icumsa - 45 RBU Max
Granulation - Fine
Color - Crystal White
Solubility - 100% Free Flowing
Also
see the Manufacture of Sugar Beet
Related
topics: Types
of Sugar, Sugar Cane, Unrefined
Sugar and Panela
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