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Mallee System
Pour rate is a key performance indicator in the development of a mallee chipper harvester. System
analysis (McCormack et al. 2009) indicates that the most efficient instantaneous pour rate for reliably
harvesting mallee should exceed 50 green tonnes /hr.
The FFI CRC project, with the current harvester, has a target instantaneous pour rate of more than 20
green tonnes/hr. The target beyond the current project is between 60 to 80 green tonnes /hr with a
subsequent prototype harvester. The prototype harvester in trials to date has achieved a maximum
continuous pour rate of 35 green tonnes/hr in a mallee crop yielding about 12 green tonnes/km of row
(about 35 green tonnes/ha). Performance in heavier crops demonstrated a similar decline to that
illustrated in Figure 2.7 due primarily to the heavier trees overloading the chipper (due to lack of
power) and reducing the continuous performance of the harvester.
In principle, higher pour rates would result in lower per tonne costs but with the restriction of a
relatively low harvester speed, at some point the mallees will need to be so big that the over-the-row
chipper harvesting method may become impractical. At this stage it is not possible to identify the
limit of performance.
2.3.3 Product bulk density
The bulk density of the product produced is an important performance consideration for efficient
transport.
Sugar System
The most critical crop factors affecting bulk density of the cane-trash mixture are stalk density, leaf
and trash to cane ratios and leaf and trash characteristics.
The ratio of trash and leaf to cane is generally accepted to be affected by variety, growing conditions
and final crop yield. A given variety can display significantly different characteristics, depending on
the environment in which it is grown.
In an assessment of the transport logistics, the breakdown of the characteristics of the total biomass is
of critical importance, i.e. extraneous matter (EM) levels alone are of limited value unless the
components of the EM are known. Extraneous matter is defined as any material other than clean
billets that occurs within the homogenous mixture of harvested biomass that is processed at the mill.
Available data on the composition of residues, with respect to fresh moisture content, are summarised
in Table 2.2.
Table 2.2 Cane supply composition (wet and dry matter basis)
Component % by weight % by moisture % DM of total EM
NSWSMC NSWSMC NSWSMC NSWSMC NSWSMC NSWSMC
1999 2000 1999 2000 1999 2000
Cane 80.2 71.5 - - - -
Tops 3.6 - 78.6 84.6 7.7 10.6
Green Leaf 10.1 28.5 66.9 67.9 33.4 36.2
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