Agriculture Reference
In-Depth Information
Box 9.5.
Other methods for cutting straw before fibre extraction.
The advantage of these alternative techniques lies in the elimination of the sectioning procedure at the
start of the extraction process.
1.
The straw is cut in the field by a Roto-Cut system. This automatic machine cuts the stem at ground
level and then, as in a silage maker, an internal mechanism cuts it into pieces of 30-50 cm in length.
These pieces are then swathed for drying (see Chapter 6 for a description of the German method - the
BAFA method). After drying, the straw is compacted into cylindrical bales. This procedure is used
mainly in Germany.
2.
Another method, described in Chapter 8 uses a straw or fodder press equipped with an integral cut-
ting device. This consists of blades that can cut the straw in advance, before it enters the compression
chamber.
3.
Finally, a bale-grinder system (using the sort of technology used for grinding household waste) is
used to chop up the bales and turn them into short pieces of straw (Trommel Systems, ECP-CPI,
ARTECH).
These different technologies, while interesting in principle, still need further improvements.
centrifugal force and break up the straw on
contact. At the end of this operation, a mix of
hurds, fibre and dust is produced. This then
needs to be subjected to a refining, or sorting,
operation.
be applied to the straw; this shock will provoke
the rupture of the stem.
TURBINE PROCESS
.
In this process - which is, to
our knowledge, used in only one factory in
Germany - the principle of wood decorticating
machinery has been applied. The straw is cut
into pieces measuring 30 cm or less and these
are passed between two vertical plates with a
diameter of 1.3 m, one turning very fast, the
other immobile.
The straw passes into the gap and literally
explodes. The resulting fibre is very fine. This
technique is both sophisticated and noisy,
requires a great deal of precise control and
appears to consume a great deal of energy.
All of these procedures, while relatively easy
to describe, are extremely precise and are very
difficult to regulate. It is necessary to find the bal-
ance between the volume of straw, the speed of
rotation and the gap between the two plates.
CRUSHER WITH ROLLERS
.
In a similar procedure
to that described above for the production of
fibres for the textile industry, the straw is passed
between two serrated rolling tables turning in
opposite directions in order to move the straw
forward. The serrations get progressively
smaller and the upper and lower rollers increas-
ingly closer to each other as they move towards
the end of the table. In this way, the straw is
subjected to an increasing onslaught as it
progresses through the rollers.
It is possible to have three or four succes-
sive beds of rollers, and the machinery can
have more than 30 pairs of rollers in total.
After a first passage, as with the ham-
mer crusher, a mix of hurds, fibre and dust is
produced, which must then be sorted and
refined.
FIBRE EXTRACTION BY STEAM EXPLOSION
.
Technol-
ogies will be described which are still at the
experimental or laboratory, rather than indus-
trial, stage.
The technique of fibre extraction by steam
explosion can be used with all sorts of fibrous
plants and has been used to decorticate hemp
and flax. It would appear to have its beginnings
in Germany during the interwar years. In 1933,
the German government, preparing for the
war effort and anticipating that the maritime
BEATING PROCESS
.
The working principles are
much the same for this process: the straw is sub-
jected to a mechanical treatment that separates
the fibre from the hurds. In this case, a beater or
thresher is used that takes its inspiration from
the threshing arms of a combine harvester.
As in the process described for the ham-
mer crusher, a high-speed tangential blow must
