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Increases in dextran in chopped cane are accompanied by slower clarification and mud filtration.
Sugar losses in processing due to dextran are indicated by the correlation of the dextran content of
process liquids and final molasses purity. Inhibition of crystallisation of sucrose by dextran results in
the formation of needle ‘long post’ (sucrose crystals elongated on the C axis) crystal rather than the
more desirable “cube” shaped crystals.
This reduces the efficiency with which sucrose may be extracted in the mill and in the refinery.
Removal of dextran in the mill is possible but is costly and hard to implement.
Deterioration is more rapid in chopped cane than wholestalk with quality losses evident in 24 hours,
or even 14 hours. In burnt cane dextran begins to form in half the time taken in green cane, and the
increase is more rapid. Dextran is reduced by minimising cut-to-crush and burn-to-crush delays.
Short and/or damaged billets, poor crop presentation and pests and diseases all increase dextran.
Dextran formation is more rapid in hot and/or humid conditions.
Hence, Australian sugar mills organise their transport scheduling to ensure that most harvested cane
is crushed within 12-16 hours of harvesting, with only a small proportion crushed 16-24 hours after
harvesting. All cane is crushed within 24 hours of harvesting unless there is a temporary transport
problem (Dawson, 2004).
Mallee System
The mixed material in chipped form is liable to decompose significantly over a period of a week. It is
preferable to sort the leaf and residues from the wood chip if wood chip is to be stored for any period
(Giles and Harris, 2003).
The need for and role of material stockpiles will need to be evaluated in terms of the supply chain
management and impact on product quality. Stockpiles are a risk management strategy and can
ensure continuous feedstock supply in case of interruptions (e.g. inclement weather, fire, flood, soft
soils, or mechanical breakdown).
Spoilage may be significant for wood chip/leaf mixtures within a week and spontaneous combustion
may be the main factor for large stockpiles. Before combustion happens, the fungal activity will make
the product an OHS issue and bind the material into a mass making future handling difficult.
Eucalyptus wood chip is relatively stable and commonly stored in open stacks for periods of several
weeks without significant loss of quality (e.g. wood chip export and paper mills). Chip is generally
the highest value product.
A chip cleaning stage to separate foliage/leaf and clean chip could be considered as part of the
process. This would allow stable storage of the chip, whilst the foliage and fine material can be
processed as quickly as possible.
The quantity of material to be stored in the stockpile is still to be determined. However the ability to
stockpile ex-harvester biomass for a few days, and sorted and dried biomass for longer periods, will
introduce significant flexibility into future mallee operations.
2.5.5 Discussion
An integrated harvesting management system will need to be developed to provide efficient harvest
and transport operations. In particular the location of loading points to provide optimal haul distances
will require careful consideration. Generally, woodchip is the highest value product and strategies for
separation of wood chip from the other biomass components will be considered. Drawing on the
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