Agriculture Reference
In-Depth Information
9.4
Treatment of Hurds
9.5
Treatment of the Powder
9.4.1 Constraints imposed
by the product
9.5.1
Characteristics of the powder
First, the characteristics of the powder are given:
The decortication of 1 t of straw produces
It should be remembered that hurds in bulk
have a density of 0.12-0.3, equating to 12-30
kg/m
3
. Bearing in mind this physical charac-
teristic, it is inconceivable that this material be
transported without compressing it severely.
It should be noted also that this material is
not very fluid and its rheological behaviour is
unpredictable and varies with humidity levels
and ambient temperature.
Finally, 1 t of straw generates between
600 and 700 kg of hurds, occupying a volume
of 5.5 m
3
.
The objective is to pack, as cheaply as
possible, the maximum amount by weight into
the smallest possible volume.
•
150 kg of powder.
This equates to a volume of 0.5 m
•
3
with a
density of between 0.2 and 0.3.
The product is abrasive.
•
9.5.2 Objective
Considering the density and pulverized nature
of the product, it requires compacting for
transport and use. One exception is that,
where the product is to be used as an enrich-
ing agent, it can be transported in bulk, pro-
viding the fields on which it is to be used are
not far away. In such cases, covered lorries or
tankers with a pneumatic loading system must
be used in order to avoid losses during
transportation.
9.4.2 General layout
of the industrial plant
To achieve the objective of maximal compres-
sion, a single technique is used.
The existing installations all adopt the
same design:
Hurds are delivered on a belt or via pneu-
9.5.3 Necessary installations
•
Taking into account the market value of the
product, procedures need to be kept cheap
and simple. An appropriate method is to use
the granulating equipment used in factories
that desiccate lucerne and other livestock
feeds.
The powder is subjected to pressure to
force it through channels; this causes the tem-
perature of the product to rise (up to around
60°C), resulting in compaction.
The end product is a pellet shaped like a
cork, with a diameter, depending on the
intended use, varying between 0.5 and 7 cm
and a length varying between 1.5 and 10 cm.
The density ranges from 0.2-0.3 to
0.6-0.7.
The product can then be bagged (for gran-
ulated animal litter and soil enrichment) and
transported.
It is also possible to manufacture bricks
that are suitable for burning in stoves and other
domestic heating systems.
matic transport into intermediary storage.
Hydraulic pressure (of the order of 150-
•
200 bars) is used to compress the hurds.
The compressed material is evacuated,
•
generally as a parallelipipedic rectangle
packed in a PVC bag. These bags are pre-
formed. 'Wrap around' techniques are
also used. As their name suggests, these
consist of the creation of a covering by
wrapping it around the compressed mate-
rial while it is still under pressure.
NB These techniques are in no way original and
are also used for the bagging up of products
such as wood chipping, cut straw and hay, etc.
9.4.3
Cost of the installations
and running costs
Costs vary, making it difficult to provide an
accurate figure.
