Sugar Production from Sugar Cane
Practical Action
are located in wooden, steel or cast iron frames.
Some of the smaller crushers, with capacities of between 200 and 500kg cane per hour, have
vertically set rolls and are animal powered but can be modified to use small engines or electric
motors. A crusher driven by a single ox can be expected to process around 50kg of cane per
hour. A 5HP diesel set could increase this to around 300kg per hour.
Others are horizontal and are usually powered by small engines or electric motors. Some small
manually powered horizontal crushers are available but they tend to be used by street vendors,
especially in South and South East Asia, to provide cane juice for drinking.
For the small-scale producer the main advantage of using automated crushers is that of
throughput rather than extraction efficiency. An extraction rate of up to 65% is achievable from
both animal driven and small automated roll mills. However, the medium to large-scale
producers use much larger roll-mills that are can extract up to 80% of the available juice
depending on the fibre content of the cane and if the cane is prepared carefully.
If greater extraction is required then it is usual to use two or more automated three-roll mills in
tandem, one behind the other. Cane is fed through the first mill and the resulting bagasse is
then fed into the second mill and so on with each stage extracting juice. Although some large-
scale factories use five three-roll mill tandems it is more usual for the larger open-pan factories
to use two or three crushers in tandem.
The pressure exerted by the mill on the cane is determined by the gap between the top roller and
the bottom rollers. If the gap is too wide then poor extraction will result; if the gap is too small
then the cane may not pass through it or may cause the rollers to jam. The correct setting of the
rollers has to be determined at the site of crushing as it
will be dependent upon the cane variety, size and
quality.
Improved extraction can be achieved by hydraulically
loading the pressure roller and by slicing or shredding
the cane along its length before crushing. This type of
system can achieve extraction of around 66%.
Another important factor for efficient extraction is the
operational speed of the crushers. Operating speeds are
typically between 5 and 50 r.p.m. The lower speeds are
easily achievable when using animal power but the use
of engines or motors requires speed reduction.
Typically diesel and petrol engines have speeds of 700
to 2000 r.p.m while electric motors are usually rated at
750 or 1500 r.p.m. Speed reduction is usually
achieved by coupling the engine to the crusher via flat
Figure 2: A Diesel powered cane
crusher with three vertical rollers in
Bangladesh. Photo: Neil Cooper
or vee type belts and pulleys. The use of flat belts is a
common and well proven technology while at the same time it is also one of the cheapest and
easiest methods. Its major draw back is the distance required between the prime mover and the
crusher to ensure maximum efficiency from the drive mechanism. Where space is limited then
vee belts and pulleys can be used as they allow for relatively close coupling. However, vee belts
and pulleys are more complicated and expensive to manufacture than flat belts and pulleys.
Direct coupling between prime mover and crusher is possible but a reduction gear box will be
required to obtain the optimum crushing speed. Compared to belt and pulley systems gear
boxes are expensive and complex requiring more maintenance.
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