Page 4 - Towards better compaction v0.5

Towards Better Compaction

Introduction

Tasmania historically sourced its wood chips from native forests, but this source has almost been
replaced by woodchips from commercial plantations.
The first Tasmanian woodchip mill was built in 1971 at Triabunna with an initial contract price of
$13.50 per green tonne (chips and moisture) to supply 610,000 tonnes of woodchips to Japanese
customers.

In the year ending September 2018, the value of Australian export woodchips was more than 1.35
billion dollars. Exports for the year were 7.336 million bone dried metric tonnes (BDMT – chips with
no moisture content) with 91% of this consisting of hardwood chips. The price of hardwood chips
averaged $207.70/BDMT in September 2018 and $230.64/BDMT in March 2019 (an increase of
approximately 12%).

Plantation timber woodchips are shipped overseas for use in papermaking. According to the
International Maritime Solid Bulk Cargoes (IMBSC) code, woodchips have a nominal bulk density of
3
326 kg/m (meaning a cubic metre of woodchips would weigh 326kg) and a nominal stowage factor
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of 3.07 m /t (meaning a tonne of woodchips would require 3.07 cubic metres of space). These
figures are indicative only, and actual supplier figures are used by the vessel to produce a loading
plan.
The bulk density is dependent upon the moisture content, and the stowage factor is dependent on
the type of wood, the way the chips were cut, their moisture content and how long they have been
left out in the open.

These figures are indicative only and vary markedly across shipments and wood types.

Calculations

Bone dry metric ton versus a green metric ton
Woodchips are bought and sold using the BDMT – the price of 1000 kg of chips with 0% moisture
content.
A green metric ton (GMT) is the price of 1000kg of chips and moisture.

Customers do not want to pay for the water content, so if we had a moisture content of 60%, a chip
content of 40% and price of $100 for a bone-dry metric ton, our customer would pay:
$ % = $ .

Stowage factor
Loading rates of up to 1000 tonnes per hour (TPH) are typical. If we achieved a load rate of 986 TPH,
3
how many cubic metres of space would be required per hour (using a stowage rate of 3.07 m /t):
. =

Bulk density
3
How much would 6000 cubic metres of chips weigh (using a bulk density of 326 kg/m )?
. =

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