Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02496298 2005-02-07
Apparatus and process for defibration of bast fiber
lp ants
This invention concerns apparatus and a process for
defibration of bast fiber plants, especially annual
plants, such as flax, hemp, kenaf, linseed straw and
jute for example.
Renewable raw materials are becoming ever more popular,
since they not only preserve existing resources, but
also make a contribution to reduce the greenhouse gas
C02. Both the fibrous fractions and the skives, which
are the woody fractions of the bast fiber plant stems,
are used in different fields of application. Processes
and apparatuses have therefore been developed to
separate the fibrous fractions and the skives in a
starting material. This process of separation is
frequently referred to as defibration or decortication.
In defibration/decortication, the starting material is
subjected to an operation of fiber-extractive
destructurization and subsequently the fibrous
fractions and the skives are separated.
The purpose of processing annual plants such as flax or
hemp is to use an adapted destructurization process to
adapt the property profile of the produced fiber to
articles which are later produced using the fibers and
to the articles' requirements. It is because of these
requirements that destructurization processes have
gained importance in recent years that utilize so-
called "green" starting materials. The difference to
traditional destructurization processes is in the field
retting in that the plant after cutting is left on the
field only for a few days to dry in order that the
residual moisture content of <18~ required for storage
may be achieved. In contrast, traditional
destructurization processes require starting materials
which remain on the field for a prolonged period,
during which weathering-based and bacterial effects
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lead to an embrittlement in order that easier
separation of the fiber from the other plant
constituents may be achieved through bending/flexing in
the course of the fiber-extractive destructization. The
plant itself consists predominantly of cellulose,
hemicellulose, pectin, lignin, water-soluble substances
and also small fatty and waxy fractions.
The fibers of the plant consist of fiber bundles. These
bundles differ in length according to fiber variety. In
the case of hemp, fiber bundle length is between about
650 mm and about 3500 mm, and in the case of flax it is
between about 100 mm and about 1400 mm. The individual
fiber in the fiber bundle is glued to the other fibers
by pectin. To obtain certain properties for later
applications, it is therefore necessary to break down
these fiber bundles to a desired level of fineness.
This is significantly more difficult in the case of the
green plant, since pectins will have degraded only to a
small extent in the course of short field rett. By
contrast, however, the high strength properties have
remained very substantially intact.
The breakup of the fiber bundles leads to fiber
shortening. It must be borne in mind here that the
fiber cell of hemp is about 10 mm to about 50 mm in
length and that of flax is about 5 mm to about 70 mm in
length. Consequently, a higher degree of fiber
extraction, and a correspondingly finer fiber, is
associated with a degree of shortening which
theoretically can take fiber length down to the length
of the individual cell.
A high input of energy is required to achieve plant
bundle breakup in the case of green starting material.
This is why prior art apparatus for this purpose
utilizes high speed assemblies which lead to breakup of
the fiber bundles through impinging, bending and
shearing stresses. There is a preference for using
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hammer mills or high speed turbinelike
destructurization systems. Fibers from aggressive
processing disaggregate from a coarse bast into many
individual fibers and fibrils. This leads to clewing
and felted structures having a wide scatter of fiber
lengths. But such high speed systems lead to the
disadvantages described. Moreover, the high energy
input takes place in a single stage and the degree of
fiber bundle breakup is then influenced by variation of
the design of the beating elements and the rotary
speed.
EP 0 744 477 B1 describes a process for defibration/
decortication of bast fiber plants wherein the starting
material is precomminuted prior to defibration/
decortication such that the starting material is
precomminuted into pieces of pour- and/or flowable
consistency and these pieces are subsequently
defibrated in a high speed rotating mill. The
subsequent separation of fibers and shives is effected
with the aid of sieves and/or sifters, at which stage
the fibers can simultaneously be classified and
fractionated according to length and also oversize,
dust and foreign bodies can be removed. Defibration is
due to the action of impact and/or rubbing and/or
shearing in the high speed rotating mills used. The
fibers generated with the aid of this process are
preferably between 1 mm and 100 mm and especially
between 2 mm and 50 mm in length.
DE 199 25 134 A1 describes a process for producing
random fiber material from plant parts which comprises
a first operating step of removing initially provided
harvested material from a stock reservoir stack, a
second operating step of forming a strand of material
having a predominantly two-dimensional alignment of the
plant parts, a third operating step of feeding the
strand of material formed into the operational region
of a processing station, a fourth operating step of
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simultaneously comminuting, disaggregating and
separating fibers and nonfibrous constituents (skives)
and a fifth operating step of separately removing the
random fiber material and the nonfibrous plant
constituents. There is an option with the known
processes of repeatedly performing at least the
procedures of destructurizing the plant parts, removing
the fractions of material produced and aftertreating
the random fiber material. The simultaneous
comminution, disaggregation and separation of fibers
and skives in a processing station can be repeated by
connecting at least two processing stations in series.
The processing stations are equipped with beating tools
having blunt hammering surfaces, which serve to
incipiently break the plant parts and, to a minor
extent, to separate the fibrous fractions from the
skives.
The present invention has for its object to provide
improved apparatus and an improved process for
defibration of bast fiber plants, especially of annual
plants, in gentle processing stages but with enhanced
efficiency for the separation of fibrous fractions and
skives. The present invention further has the purpose
to enhance the fraction of fibers and/or skives having
predetermined properties for further processing,
especially having a predetermined length.
This object is achieved according to the present
invention by apparatus according to independent claim 1
and also a process according to independent claim 11.
Apparatus for defibration of bast fiber plants,
especially annual plants such as flax, hemp, kenaf,
linseed straw and jute, having comminuting means for
precomminuting a starting material and having an
intermediate store in which the precomminuted starting
material is received and from which the precomminuted
starting material is dispensed for a metered feed to a
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downstream processing sector for fiber-extractive
destructurization and for separation of fiber fractions
and skives, wherein a series arrangement of plural
coarse destructurizing means and plural fine
destructurizing means is formed along the processing
sector which is meteredly fed with the precomminuted
starting material.
The series arrangement of coarsely destructurizing
means and finely destructurizing means makes it
possible to specifically influence fiber fineness and
skive size by subjecting the precomminuted starting
material along the processing sector to plural
destructurizing procedures, for which coarsely
destructurizing means and finely destructurizing means
are freely combinable with each other in the series
arrangement according to the particular application. A
cascadelike processing procedure where the arrangement
of coarsely destructurizing and finely destructurizing
means can be adapted to separate fiber fractions and
skives having predetermined properties for further
processing is made possible.
In an advantageous embodiment of the invention along
the processing sector there is an alternating
arrangement of one of the plural coarsely
destructurizing means and one of the plural finely
destructurizing means, whereby an alternating
coarse/fine destructurization of the comminuted
starting material can be implemented.
Combined with the plural coarsely destructurizing means
and the plural finely destructurizing means, sieves
and/or sifters can be provided in the series
arrangement in one embodiment of the invention for
separating fiber fractions and skives along the
processing sector and/or at the end of the processing
sector. At the same time, in this embodiment, a
classification and fractionation of the fiber
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fractions/shives according to length can take place.
In an advantageous embodiment the plural coarsely
destructurizing means each comprise one drum and,
disposed in the drum, rotatable beating elements for
processing the precomminuted starting material, the
rotatable beating elements being arranged on a shaft to
be pivotable. The beating elements are turned by means
of a shaft in the drum to process the material, and in
the course of this turning movement perform pivoting
movements due to the pivotable arrangement. The use of
such coarsely destructurizing means has the advantage
of providing a way to coarsely destructurize the
starting material by shearing, rubbing, impact and/or
beating that is less costly than known high speed
rotating mills, for example hammer mills.
In one embodiment of the invention the rotatably
mounted beating elements can be pivotably mounted on a
shaft housing and can be pivotable about an axis
parallel to the center line of the shaft. This creates
beating elements which work like mallets in that they,
as the shaft in the drum turns, additionally pivot
around an axis formed outside the center line of the
shaft and thus act as mallets.
To improve energy input onto the material processed in
the coarsely destructurizing means, one embodiment of
the invention envisions that the rotatably mounted
beating elements are paddle shaped. A particular
achievement of this is that the beating and entraining
effect exerted by the beating elements on the material
to be processed is improved.
In one embodiment of the invention the paddle-shaped
beating elements may have at a distal end (distal
relative to the shaft) a paddle surface which is curved
longitudinally to the shaft and/or transversely to the
shaft, whereby a further improvement in the
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transportation in the coarsely destructurizing means of
the material to be processed is achieved. The paddle
surfaces of beating elements can be arranged adjacent
to each other in the longitudinal direction of the
shaft and offset relative to each other in the
circumferential direction of the shaft such that an
essentially uninterrupted area is formed were these
beating elements to be displaced along a straight line
in the longitudinal direction of the shaft. The number
and distribution of the beating elements on the shaft
can also be chosen such that an essentially
uninterrupted area is repeatedly formed. The
essentially uninterrupted area optimizes the energy
input onto the material to be processed.
The running properties of the coarsely destructurizing
means are improved in an advantageous further
development of the invention when the rotatably mounted
beating elements are arranged on the shaft along one or
more spiral lines extending in the longitudinal
direction of the shaft. One possibility here is that
the rotatably mounted beating elements are positioned
essentially along a spiral line extending around the
shaft. The beating elements can advantageously each be
disposed with a lateral offset to such an orbiting
spiral line, so that they are positioned essentially
along a spirally orbiting zigzag or curve line. The
arrangement along a spiral line prevents a pulsing
operation, avoiding higher stress on bearing elements.
It is further ensured thereby that plant material
cannot get stuck and that there can be no wraps around
the shaft.
The rotatably mounted beating elements may have an
outer beating surface having blunt edges. Blunt edges
prevent an inadvertent cutting effect when
destructurizing the comminuted starting material. In
addition, blunt edges improve the impinging effect.
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In order that the residence time of the precomminuted
starting material in the drum may be increased, which
leads to an improved destructurizing and separating
effect in the individual coarsely destructurizing
means, it is envisaged in one embodiment of the
invention that plural impinging elements which extend
in the longitudinal direction are arranged on an inner
surface of the drum. The impinging elements may be for
example angular or u-shaped impinging elements where
angled portions project from the inner surface.
The starting material may be precomminuted in the
comminuting means into pieces from about 80 mm to about
120 mm, preferably from about 120 mm to about 160 mm
and more preferably from about 160 mm to about 200 mm
in length. One consequence of this is that the starting
material is precomminuted to a desired starting length
which in turn significantly influences the length
obtained for fiber fractions and skives in the course
of the destructurization and separation of these
constituents. Precomminution to such lengths, moreover,
facilitates automated processing of the precomminuted
starting material along the processing sector in the
plural coarsely destructurizing means and the plural
finely destructurizing means.
An additional benefit of precomminution is that the
fiber fractions separated in the course of the
processing sector by destructurization of precomminuted
starting material have a length and fiber fineness
which, when the fiber fractions are used in insulant
products, for example insulant panels, provide the
thermal conductivity necessary for the insulating
effect. The disclosed process for separating the fiber
fractions may thus be advantageously used in
conjunction with a process for producing an insulant
product, especially an insulant panel, such that the
separated fiber fractions are mixed with a base
material, for example a plastic, and formed into shaped
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articles, in a processing station downstream of the
processing sector.
Illustrative embodiments of the invention will now be
more particularly by way of example with reference to a
drawing where the sole figure shows a schematic
depiction of apparatus for defibration of bast fiber
plants, especially renewable raw materials.
Referring to the figure, a starting material 1 is fed
to a comminuting apparatus 2. The starting material 1
is haulm material of bast fiber plants, such as flax,
hemp, kenaf, linseed straw or jute for example. The
starting material 1 is preshortened into haulm sections
of uniform or approximately uniform length. A thus
preshortened starting material 3 then arrives in an
intermediate store 4. The starting material 1 is
preshortened to a length which is preferably in the
range from about 80 mm to about 120 mm, more preferably
in the range from about 120 mm to about 160 mm and even
more preferably in the range from about 160 mm to about
200 mm and then fed to the intermediate store 4.
From the intermediate store 4, the preshortened
starting material 3 can then be metered onto conveying
means 5 for feeding the preshortened starting material
3 to a downstream processing sector for destructurizing
and for separating fiber fractions and skives. The
preshortened starting material 3 is fed via the
conveying means 5 to a first dynamic destructurizing
unit which is coarse destructurizing means 6 in which
the preshortened starting material 3 is subjected to
coarse destructurization. A first coarse separation of
fibers and skives takes place in this processing stage.
The coarsely destructurizing means 6 comprises a
partially open shell surface. The open region of the
shell surface has not only an inlet opening for taking
in the material to be processed in the coarsely
destructurizing means 6 but also an outlet opening for
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removing the processed material, and this constitutes a
simplified engineering construction. The centrifugal
force whirls the processed material through the outlet
opening onto the conveying means 5, ensuring a constant
transportation.
Within the drum-shaped shell surface is disposed a
rotor which is advantageously formed to incorporate a
shaft and equipped with blunt flat and/or curved
beating elements. The number of these beating elements
on the rotor is variable. The beating elements are
preferably arranged on the rotor along one or more
spiral lines extending around the rotor, as individual
elements distributed on a rotatable shaft.
The skives separated off are subsequently sieved off
via a sieve sector. The coarsely destructurizing means
6 is followed by finely destructurizing means 7 in turn
followed by further coarsely destructurizing means 8.
Thereafter, the comminuted starting material 3 is
processed in two further finely destructurizing means
9, 10. Along the processing sector, sieves/sifters (not
depicted) may be combined with the coarsely
destructurizing means 6,8 and the finely
destructurizing means 7,9,10 to separate the fiber
fractions and skives. The depicted series arrangement
of the coarsely destructurizing means 6,8 and the
finely destructurizing means 7,9,10 is illustrative.
Depending on the particular application, any
combination of the appliances in the series arrangement
can be chosen.
The coarsely destructurizing means 6,8 are formed with
the aid of a respective dynamic destructurizing
appliance which comprises a drum 6a,8a and also beating
elements 6b,8b rotatably mounted in the drum 6a,8a. The
beating elements 6b,8b are paddle or shovel shaped and
mounted on a shaft 11 which serves to rotate the
beating elements 6b, 8b in the drum 6a, 8a. The beating
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elements 6b,8b are pivotably secured to the shaft 11,
so that they can perform additional pivoting movements
as the shaft 11 turns. In addition, this form of
attachment permits quick and economical replacement.
The beating elements 6b,8b are preferably distributed
along one or more spiral lines extending in the
longitudinal direction of the shaft 11. This makes for
a very large operating width, amounting to several
meters for example, which permits a high throughput.
Paddle or shovel surfaces for the beating elements
6b,8b are preferably dimensioned such that the paddle
or shovel surfaces of beating elements distributed
along one or more of the spiral lines around the shaft
11 are arranged adjacent to each another in the
longitudinal direction of the shaft 11 and offset
relative to each other in the circumferential direction
of the shaft, so forming an essentially uninterrupted
area were these beating elements to be displaced along
a straight line in the longitudinal direction of the
shaft 11. The number and distribution of the beating
elements 6b,8b on the shaft 11 can also be chosen such
that an essentially uninterrupted area is repeatedly
formed. The essentially uninterrupted area optimizes
the energy input onto the material to be processed.
On an inner surface 6c,8c of the shell surface are
arranged plural impinging elements 6d,8d which are
preferably formed as profiled retaining strips and
serve to lengthen the residence time of the comminuted
starting material 3 in the respective drum 6a,8a, to
enhance the energy input whereby the defibration/
decortication performed by shearing, rubbing, impinging
and/or beating is made more effective. The number and
spacing of the impinging elements 6d,8d fixed
preferably on the inner surface 6c,8c are variable. The
plural impinging elements 6d,8d may be angular or u-
shaped elements where angled limbs project from the
inner surface 6c,8c. The rotatably mounted beating
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elements 6b,8b have an outer beating surface having one
or more blunt edges.
The finely destructurizing means 7,9,10 each have
static and rotating combing elements which are spaced
apart and intermesh when the rotating combing elements
rotate past the static combing elements.
The destructurizing process described in conjunction
with the illustrative embodiment can be summarized as
follows. The coarsely destructurizing means 6 provides
a first coarse separation of fibers and skives. The
shines separated off are subsequently sieved off via a
sieve sector (not depicted). Sieve sectors are known as
such and therefore are not more particularly described
herein. The residual fraction is fed to finely
destructurizing means 7. This machine unit comprises
comblike segments which are static and rotatory and, by
means of intermeshing combing elements, lead to a
separation of adherent shines and previously broken up
fiber bundles. The detached shines are subsequently
sieved off and the remaining material is fed for coarse
destructurization to the further coarsely
destructurizing means 8, comparable to the coarsely
destructurizing means 6. By virtue.of the separation of
aliquots (skives) in preceding processing steps, this
processing station is fed with a distinctly reduced
amount of material, so that the energy input for coarse
destructurization is now only applied to the remaining
fiber bundles and to the fiber bundles having as yet
undetached skives. This is followed by further finely
destructurizing means 9 with subsequent sieve sector.
This fiber material is then fed to finely
destructurizing means 10 for skives separation.
Following this processing stage, the fibers exhibit a
high degree of isolation coupled with a low residual
skives content. If necessary, finely destructurizing
means 10 can be followed by further downstream finely
destructurizing units and/or sieve sectors.
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The features of the invention which are disclosed in
the preceding description, the claims and the drawing
can be significant not only individually but also in
any desired combination to actualize the invention in
its various embodiments.
15
25
35
List of reference numerals
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List of reference numerals:
1 Starting material
2 Comminuting means
3 Precomminuted starting material
4 Intermediate store
5 Conveying means
6,8 Coarsely destructurizing means
6a,8a Drum
6b,8b Rotatably mounted beating elements
6c,8c Inner surface of drum
6d,8d Impinging elements
7,9,10 Finely destructurizing means
11 Shaft
25
Claims
