Harvasting
Sugar cane is harvested by cutting down the stems close
the ground level but leaving the shoot underground so that it re-grows in time for
the next crop. Harvest times tend to be during the dry season and the length of
the harvest ranges from as little as 2 months up to 11 months. The cane
is taken to the factory: often by truck or rail wagon but sometimes on a cart pulled
by a bullock or donkey!
Extraction
The first stage of processing is the extraction of
the cane juice.in many factories the Cane is crushed in a series of large roller
mills: to a mangle (wringer) which was used to squeeze the water out of clean washing
a century ago. The sweet juice comes gushing out and the cane fibre is carried away
for use in the boilers. In other factories a diffuser is used as is discribed for
beet suger manufacture.Either way the juice is pretty dirty: the soil from the fields,
some small fibreas and the green extracts from the plant are all mixed in with the
suger.
Evaporation
The factory can clean up the juice quite easily with
slaked lime (a relative of chalk) which settles out a lot of the dirt so that it
can be sent back to the fields, Once this is done, the juice is thickened up into
a syrup by boiling off the water using steam in a process called evaporation.Sometimes
the syrup is cleaned up again but more often it just goes on to the crystal-making
steps without any more cleaning. The evaporation is undertaken in order to improve
the energy efficience of the factory.
Boiling
The syrup placed into a very large pan for boiling,
the last stage. In the pan even more water is boild off until conditions are right
for sugar crystals to grow. You may have done something like this at school but
probable not with sugar because it is difficult to get the crystals to grow well.
In the factory the workersusually have to throw in some sugar dust to initiate crystal
formation. Oncce the crystals have grown the resulting mixture os crystal and mother
liquor is spun in centrifuges to separate the two, rather like washing in spin dried.Thecrystals
are then given a final dry with hot air before being stored ready fore despatch.
Storage
The final raw sugar forms a sticky brown mountain in
the stoer and looks rather like the soft brown sugar found in fomestic kitchens.
It could be used ilke that but usually it gets dirty in storage and has a distinctive
taste which most people don't want . That is why it is refined when it gets to the
country where it will be used. Additionally,because one can not get all the sugar
out of the juice, there is a sweet by-product made: molasses. This is usually turned
into a cattle feed or is sent to a distillery where alcohol is made.
Power
So what happened to all that fibre from crushing the
sugar cane? It is called "bagasse" in the industry. The factory needs electricity
and steam to run, both of which are generated using this fibre.The bagasse is burnt
in large in furnaces where a lot of heat is given out which can be used in turn
to boil water and make
high pressure steam.The steam is than used to drive a turbine
in order to make electricity and create low pressure steam for the sugar making
process that makes most of our electricity but there are several important difference.When
a large power station produces electricity it burns a fossil fuel (once used, a
fuel that cannot be replaced) which contaminates the atmosphere and the station
has to dump alot of low grade heat.All this contributes to global warming. In the
cane sugar factory the bagasse fuel is renewable and the gases it produces, essentially
CO2, are more than used up by the new cane growing. Add to that the factory use
of low grade heat (a system called co-generation) and one can see that a well run
cane sugar estate is environmentally friendly. |