Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND SYSTEM FOR PREPARING
DENSIFIED LIGNOCELLULOSIC PULP FOR USE IN
THERMOPLASTIC COMPOSITE MANUFACTURING PROCESSES
FIELD OF THE INVENTION
The present invention relates generally to the field of
lignocellulosic/thermoplastic
composite materials. The present invention more particularly relates to the
field of
processing, metering, and feeding densified lignocellulosic pulp into
thermoplastic
composite manufacturing processes.
BACKGROUND OF THE INVENTION
Lignocellulosic/thermoplastic composites are materials that combine
thermoplastic
polymers with lignocellulosic materials, which are used as either
reinforcements or
fillers. The advantages of such composites are well documented in prior art
such as in
Canadian Patent Application No. 2,527,325 (Sain et al.).
There are numerous sources of lignocellulosic materials that may be used as
thermoplastic composite fillers or reinforcements. Such sources may include
both wood
and non-wood based materials. Non-wood based materials may include bast and
leaf
fibres taken from agricultural crop such as hemp, flax, wheat, and sisal.
There are also various mechanically or chemically processed forms of supplying
such lignocellulosic materials depending on the source. Such forms include:
powders or
particulates including wood flour and sawdust, chopped fibres or strands,
continuous
rovings, woven and non-woven mats, and pulp.
Pulp fibres are generally a product of lignocellulosic materials that have
been
processed through a combination of chemical and/or mechanical pulping
processes. Such
processes including Kraft and Mechanical pulping are well known within the
pulp and
paper industry. Although lignocellulosic pulp can be produced from
agricultural fibre
sources, by far the largest source of pulp in the world is wood for use in
papermaking,
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paperboard, and absorbent products applications.
Most lignocellulosic pulps are densified and packaged into a baled form, which
represents a low-cost method of storing and transporting such raw materials.
More
specifically, bales of commercially available wood pulp represent a large and
relatively
reliable supply of lignocellulosic fibres for use in thermoplastic composites
applications.
There are numerous conventional processes that are used to combine
lignocellulosic
materials with thermoplastics, most of which are well known to those skilled
in the art of
plastics processing. Such processes include extrusion, compounding,
compression
molding, injection molding, and combinations or variations thereof.
To date, the majority of conventional and commercially available
lignocellulosic-
thermoplastic composites use lignocellulosic materials that are supplied in
the form of
powders such as wood flour. As such, feeding difficulties into such
manufacturing
processes are reduced, as powders are better flowing than fibrous materials.
The other
major category of conventional lignocellulosic/thermoplastic composite
materials
includes compression-molded parts, however in this case feeding issues are
diminished as
the fibres are typically placed into an open mold and are supplied in various
forms of
mats.
The feeding of fibrous materials into plastics molding or compounding machines
such as extruders are well-known challenges in the thermoplastic composites
field. If the
bulk density of the material is too low, or if the fibre lengths are too long,
"bridging"
occurs. "Bridging" refers to a case where the material does not flow, and is
in effect
clogging transition points in the process, such as at the feed throat of an
extruder.
In the fields of both glass and lignocellulosic fibre reinforced
thermoplastics,
numerous approaches have been used to solve problems of feeding and bridging.
Many
solutions to feeding fibrous materials are also linked with other technical
requirements,
including mechanical performance.
An increased fibre length is often desired in thermoplastic composite
applications
to maximize mechanical properties. However, the flowability of fibrous
materials
decreases with increasing fibre lengths. One solution to this problem is to
change the
nature of the process and provide fibrous material in the form of yarns or
continuous
rovings. In this case the rovings are "pulltruded" and subsequently cut and
mixed
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through an extruder. The disadvantage of such a process is that producing
rovings or
yarns increases the raw material costs.
Barlow et al. in United States Patent No. 6,743,507 (2004) describe a process
in
which lignocellulosic pulp is first converted into a densified pellet using a
water-soluble
binder for ease of feeding. It requires that the fibres in sheet form be first
broken into
discrete bundles, which in turn are pelletized with the binder. The addition
of both these
steps and the use of binding chemicals would add cost to the process. Another
embodiment of the invention involves capturing and pelletizing the pulp at the
mill
before it is formed into sheets. This embodiment does not allow for the use of
commercially available market pulp.
Dezutter et al. in United States Patent No. 6,811,879 disclose a new form of
flake
pulp having a specific size, density and wet dispersibility, that may be
metered in
specified quantities when adding to cementitious products due to the fact that
bulk
quantities of the flakes flow well in conduits and other enclosed containers.
Dezutter et
al. in United States Patent No. 6,837,452 further discloses a process for
dewatering liquid
pulp stock to produce singulated pulp flakes. Such flakes may be sent to a
baler for
packaging.
Dezutter and Hansen in United States Patent Nos. 7,201,825 and 7,3.06,846
disclose
a process for making discrete particles of cellulosic material that are
flowable and
meterable. Such particles comprise singulated cellulose fibres that have been
densified.
Process aids may be added to assist in the flow of fibrous materials. Khavkine
et al.
in United States Patent No. 6,883,399 (2004) incorporate a blend of flax bast
fibres and
shives for improved flowability. Shimada et al. in United States Patent No.
5,087,518
(1992) combine a mixture of glass flakes and fibres to provide for a free-
flowing
reinforcing material in thermoplastic resins.
Despite the numerous sources and forms of lignocellulosic materials available,
and
the existing techniques of feeding fibrous materials, there is a need for a
process capable
of supplying densified lignocellulosic pulps into a variety of thermoplastic
composite
manufacturing processes. The process should meet the particular requirements
of such
composite manufacturing processes including supplying pulp without any feeding
difficulties, and should enable precise control of the feed rates.
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The present invention meets the aforementioned requirements and is capable of
delivering lignocellulosic pulp into composite manufacturing processes without
any
bridging effect. It allows for the use of conventional market pulp, is readily
scalable, and
is capable of integrating directly into any thermoplastics composite
manufacturing
process, whether operating in continuous or batch modes.
SUMMARY OF THE INVENTION
In one aspect, the present disclosure relates to a method of preparing dense
lignocellulosic fibre aggregates for use in manufacturing high performance,
recyclable
and moldable lignocellulosic fibre and thermoplastic composites, or articles
made of the
high performance, recyclable and moldable lignocellulosic fibre and
thermoplastic
composites, characterized in that it comprises the steps of. feeding a
densified form of
lignocellulosic fibre into a size reduction device; and size reducing the
densified form of
lignocellulosic fibre so as to produce dense lignocellulosic fibre aggregates
having an
average size profile suitable for use in manufacturing high performance,
recyclable and
moldable lignocellulosic fibre and thermoplastic composites, or articles made
of the high
performance, recyclable and moldable lignocellulosic fibre and thermoplastic
composites.
In another aspect, the present disclosure relates to a system for preparing
dense
lignocellulosic fibre aggregates for use in manufacturing high performance,
recyclable
and moldable lignocellulosic fibre and thermoplastic composites, or articles
made of the
high performance, recyclable and moldable lignocellulosic fibre and
thermoplastic
composites, characterized in that it comprises: a size reduction apparatus
operable to size
reduce a densified form of lignocellulosic fibre so as to produce the dense
lignocellulosic
fibre aggregates having an average size profile suitable for use in
manufacturing high
performance, recyclable and moldable lignocellulosic fibre and thermoplastic
composites, or articles made of the high performance, recyclable and moldable
lignocellulosic fibre and thermoplastic composites.
BRIEF DESCRIPTION OF THE DRAWINGS
A detailed description of the preferred embodiment(s) is (are) provided herein
below by
way of example only and with reference to the following drawings, in which:
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FIG. 1 illustrates a block process diagram of one embodiment of the present
invention;
FIG. 2 illustrates a typical Bleached Kraft pulp bale;
FIG. 3 illustrates a typical flash dried High-Yield pulp bale;
FIG. 4 illustrates an example low-speed high-torque system with vertical feed;
FIG. 5 illustrates an example low-speed high-torque system with horizontal
feed;
FIG. 6 illustrates a cross sectional view of a screw within a tube
FIG. 7 illustrates an example loss-in-weight screw feeding system with rotor
agitation;
In the drawings, one embodiment of the invention is illustrated by way of
example.
It is to be expressly understood that the description and drawings are only
for the purpose
of illustration and as an aid to understanding, and are not intended as a
definition of the
20 limits of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a method and system for producing dense fibre
aggregates
from a densified mass of lignocellulosic fibre, for example, a densified bale.
As a skilled
reader will recognize, the present invention may utilize densified forms of
lignocellulosic
fibre other than baled pulp. It should also be understood that a "bale" in
this disclosure
refers to a densified mass regardless of shape, dimension, or method of
forming the bale.
Dense fibre aggregates are produced by way of a dense fibre aggregate
production device
whereby aggregates of pulp are produced through gentle size-reduction of the
lignocellulosic fibre. This removal occurs without any significant
"defiberization effect"
or reduction in density of the pulp. Also, the dense fibre aggregate
production device is
disposed to remove fibre aggregates with minimal shearing action on the
individual
fibres, thereby preserving fibre length.
The densified fibre of the present invention may be produced to provide
particular
benefits for feeding into thermoplastic composite manufacturing processes,
when for
example, using loss-in-weight feed systems: (a) it provides relatively narrow
particle size
distribution; and (b) exhibits reduced "bridging" at feeding and transition
points during
the composite manufacturing process. Such properties are also beneficial for
feeding into
processes following size reduction and preceding thermoplastic composite
manufacturing
processes ("intervening processes").
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In another aspect of the invention, the density of the fibre is substantially
maintained during any intervening processes. Accordingly, the densified fibre
yielded by
the method and system of the present invention may be stored, conveyed or fed
through
systems and processes prior to any composite manufacturing process. The
density of the
lignocellulosic fibres is maintained throughout the method and process whereby
the
dense fibre aggregates can provide individual particle densities approximately
equal to, or
substantially the same as, the density of the lignocellulosic fibre in the
originally supplied
densified form
A first aspect of the present invention involves a method of preparing
densified
lignocellulosic fibre aggregates from lignocellulosic fibre which includes
obtaining the
densified mass of lignocellulosic fibre by means of a process for forming the
densified
mass of lignocellulosic fibre. A second aspect of the present invention,
involves a
method of preparing densified lignocellulosic fibre aggregates from
lignocellulosic fibre
obtained in a densified bale form.
The use of baled lignocellulosic pulp in thermoplastic composites is an
unconventional application in an industry that is designed to service
papermaking and
absorbent products manufacturers. The two key issues to be addressed when
using baled
lignocellulosic pulp for composites applications are the conversion of the
pulp bales into
a suitable form that can be subsequently fed into any conventional
thermoplastic
composites manufacturing process, and the precise feeding of such pulp into
the
manufacturing process. The overall method is illustrated having regard to FIG.
1.
Because papermaking is the primary application of pulp bales, there is
typically no
need for dry processing as the entire bale is thrown into a tank of water or
"hydra-
pulper". Thermoplastic composite manufacturing processes on the other hand,
require
pulp with low moisture content. As such, for composites manufacturing the
advantage of
using water to break apart or dissolve the bales is lost.
For absorbent product applications, the pulp bales are typically processed
dry. The
difference is that a low bulk density "defiberized" form of the pulp is
required, which in
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thermoplastic composite applications would cause the bridging effect during
feeding.
For the purposes of this invention, "lignocellulosic pulp" is defined as any
lignocellulosic fibrous material that has been manufactured using either
chemical or
mechanical pulping processes or combinations of both. Such processes include:
the Kraft
process, Sulphite processes, or the family of High-Yield pulping processes.
Some
examples of High-Yield pulping processes include: Thermomechanical pulps
(TMP),
Chemithermomechanical pulp (CTMP), and Bleached Chemithermomechanical pulps
(BCTMP). The pulp can be from both wood and non-wood sources such as
agricultural
fibres as well as both virgin and recycled fibres. It should be noted that
while
lignocellulosic fibres in pulp form are preferred in the present invention,
other forms of
lignocellulosic fibres such as those exposed to enzymatic treatments may also
be
processed.
The bale density referred to in this embodiment should usually define the
theoretical maximum density of material eventually fed into the downstream
thermoplastic composites manufacturing process. This bale density may be
controlled
during sheet forming or compression of the bales, depending on the pulping
process.
The largest source of lignocellulosic pulp is from commercially available wood
pulps such as Bleached Kraft pulps or High-Yield pulps. Commercially available
Bleached Kraft pulp bales typically consist of individual sheets of pulp that
have been
dried and stacked to form a complete bale as depicted in FIG. 2, whereas High
Yield
pulp bales typically consist of a homogenous mass of pulp that has been flash
dried and
pressed in molds into individual blocks or "cookies". The "cookies" are then
typically
stacked four-high to form a complete bale as depicted in FIG. 3. Kraft pulp
bales
typically weigh 500-600 lbs with densities between 0.8-1.1 g/cm3, while flash-
dried bales
of Chemithermomechanical pulp weigh between 300-500 lbs and have densities
between
0.5-0.9 g/cm3. Both types of bales are shipped "dry", meaning approximate bone-
dry
moisture content of between 10-16%.
When provided with lignocellulosic pulp bales, there have been prior art
methods
have attempted to size-reduce such bales for other applications such as
sanitary napkins
and diaper manufacturing. Examples of such methods may include cutting or
splitting
the bale into sheets or slabs, as well as exposing the bale to various forms
of high-impact
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or high-speed milling or grinding, such as hammermills. Such processes
however, do not
produce forms of the pulp that are suitable for thermoplastic composites
manufacturing
processes.
When exposing the bales to various forms of high-impact or high-speed
grinding,
the bulk density of the pulp is drastically reduced, and large amounts of dust
are
produced. Pulp converted through such processes is extremely difficult to feed
due to its
low bulk density form.
The present invention uses an alternative strategy for converting
lignocellulosic
pulp bales into a form suitable for feeding. Instead of using the previously
described
techniques, the present invention is capable of directly converting the bales
through the
production of "Dense Fibre Aggregates" from the bale surfaces. This is done
without any
prior modifications or processing conducted on the bale. Such dense fibre
aggregates are
suitable for controlled feeding into a variety of thermoplastic composite
manufacturing
processes. The present invention also maximizes retention of fibre length and
minimizes
production of dust.
Dense fibre aggregates are defined as particles of approximately 0.2-3.0 inch
in
width, more preferably 0.5-1.0 inch in width, and with individual aggregate
densities that
are close to the pre-converted density of the pulp bale. Such aggregates may
be in a
variety of shapes such as oval, rectangular, cubic, or discs. In the case of
oval or circular
shaped aggregates "width" is defined as the diameter, while for irregular or
rectangular
shaped aggregates, "width" is defined as the longer of the two cross sectional
dimensions.
Depending on the pulp source and type of bale, the aggregates may also have
varying
thickness. For example, when taken from Kraft pulp the aggregates would have a
lower
thickness (flake form) than from flash-dried high-yield pulp bales.
Typically the individual aggregate densities will be higher than the bulk
density, as
the latter is determined by how the individual aggregates pack together, and a
densified
bale represents approximately the highest packing density. The dense fibre
aggregate
bulk densities are typically between 0.1-0.8 g/cm3. Preferably, densities of
the individual
aggregates are equal to the original bale density. The dense fibre aggregates
produced by
the present invention may have a narrow particle size distribution, and may
not
experience "bridging" at feeding and transition points during the process so
long as their
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density is approximately maintained. Due to their narrow size distribution,
controlled
and even feed rates may be achieved.
FIG. 1 illustrates a block diagram of one particular embodiment of the present
invention. A lignocellulosic pulp bale 20 is fed into a dense fibre aggregate
production
device 21. The bale may be fed using any standard conveying means, such as a
belt
conveyor. In one embodiment of the present invention, the dense fibre
aggregate
production device is a machine equipped with one or more shafts or "rotors"
rotating at a
"low-speed", where each rotor has a series of cutters or protrusions. The bale
is pressed
against the low-speed rotors in order to produce the dense fibre aggregates.
By operating
the rotors at low-speed, the dense aggregates of pulp may be gently removed
directly
from the bale surface by the cutters without any significant "defiberization
effect" or
reduction in density of the pulp. The cutters remove fibre aggregates from the
surface of
the bale without imposing any severe shearing action on the individual fibres,
therefore
fibre length may also be well preserved.
One example of such a dense fibre aggregate production device is a low-speed
high-torque shredder FIG. 4 and FIG. 5 equipped with a screen 50 and with one
or more
rotors 51, each rotor comprising protrusions, blades or cutters at defined
spacings. Such
shredders are commercially available from companies such as SSI Shredding
Systems.
Devices of this type may operate either vertically or horizontally, meaning
that the bale is
placed on top of the rotors in the vertical case FIG. 4, or the bale is
pressed horizontally
against the rotors FIG. 5.
It is important to note that while there are numerous size-reduction devices
that
operate on the principle of cutting or shearing rotors, the discussed
embodiment of the
present invention requires operation at low-speed and high-torque. "Low-speed"
refers to
machines operating at rotations per minute (RPM) preferably below 150 RPM,
more
preferably below 90 RPM, although RPM settings chosen and actual results may
depend
on other factors such as the dimensions of the cutters and diameter of the
rotor. In
general, low-speed high-torque operation differs from size reduction processes
that
appear to be similar such as granulators or hammer mills, which operate at or
above
several hundred RPM. Due to the lower RPM at operation, an increased torque
must be
maintained when compared to typical granulators in order to extract the dense
aggregates.
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The differences when operating at low-speed and high-torque compared to
similarly
configured devices operating at a higher RPM are apparent when examining the
converted product, as the density of the pulp is well preserved when the RPM
is
maintained at a low level and the dense aggregates are produced. Increasing
RPM will
lead to a drastic decrease in bulk density, and instead of dense aggregates a
fluffy form of
the pulp is produced. For example, a typical pulp bale at bale density of 0.6
g/cm3 may
be reduced to a bulk density of 0.02 g/cm3 if processed at RPMs over 150. Such
low
densities cause severe bridging and feeding difficulties. Increasing RPM also
leads to an
increased production of dust.
Depending on the scale of the compounding or molding process 24, a variety of
mass throughputs at dense fibre aggregate production 21 may be required. In
addition,
pulp bales may be supplied in a variety of dimensions. The number and
configuration of
the rotors may affect both the throughput and bale handling capability of the
aggregate
production system. For example a four-rotor system may be capable of handling
larger
bales, and/or have higher throughput than a single rotor system. The size and
number of
rotors of the aggregate production system however, are simply a function of
scale and not
necessarily a primary element of the principle of the present invention.
The combination of process variables such as: pulp bale type, starting bale
density,
screen size/shape, and cutter shape/spacings will define the final size and
shape of the
dense fibre aggregates, which is matched to the throughput and size of the
feeding step 23
as well as the. resulting composite manufacturing process being fed 24. A
narrow and
controllable aggregate size distribution is maintained through the adjustment
of such
variables.
In order to maintain sufficient pressure of the bale against the rotors for
dense fibre
aggregate production to occur, it is desirable to use either the weight of
additional bales
which are fed continuously on top of the current bale being processed, or to
use a device
such as a "ram" to maintain pressure as the weight of the bale decreases while
the
aggregates are being produced. A ram is a device that applies pressure onto
the bale
against the rotor, and is often powered through a hydraulic system. Such a
device may
apply pressure downward in the case of a vertically fed size reduction system,
as shown
in FIG. 4, or horizontally in the case of a horizontal system, as shown in
FIG. 5. If
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sufficient pressure is not maintained, the bale may "float" on top of the
rotors and
production of dense fibre aggregates may not occur.
Following the production of dense fibre aggregates, it is important that the
density
of the aggregates be substantially maintained up to the point of entry into
the composite
manufacturing process 24. Drastic reduction in density may lead to bridging
problems at
subsequent feeding or handling steps. The dense fibre aggregates are conveyed
22 either
to temporary storage, or directly to a feeding system 23. Optionally, the
dense fibre
aggregates may also be conveyed to a dryer for moisture content reduction
before further
feeding into the composites manufacturing process. If the dense fibre
aggregates are
temporarily stored or dried before feeding, a secondary feeding and conveying
system
operating on similar constraints discussed should be used.
Thus any number of systems and related processes including storage, conveying,
or
feeding, occurring in between the steps of size reduction 21 and the
composites
manufacturing process 24 should be provided such that there is minimal
reduction in pulp
density.
The final step of the present invention involves feeding 23 the dense fibre
aggregates into typical equipment used in thermoplastic composite
manufacturing
processes 24. Such processes may include extrusion (for example single or twin-
screw
extrusion), compounding, injection molding, or combinations thereof, such as
in-line
compounding and injection molding systems. Typically, equipment used in such
manufacturing processes have feed throats with associated hoppers mounted on
top. The
aggregates are fed into the hopper and are discharged by gravity downwards
into a
rotating screw. In order for the aggregates to properly flow from the hopper
into a screw,
the density must again be maintained during the feeding step 23 to prevent
"bridging" at
the throat of the equipment used for composite manufacturing. The feeding step
must
also allow for precise control of feed rates in order to determine the exact
mass flow rate
of aggregates being fed either in continuous or batch processing.
In one embodiment of the present invention, the dense fibre aggregates are fed
using at least one rotating screw, more preferably a spiral screw, however any
screw that
does not cause reduction in density of the aggregates may be used. The screw
is typically
mounted within a tube of approximately the same length. A spiral screw is
preferred
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because its open spiral design allows aggregates to be conveyed without much
reduction
in density and the aggregates will not "pack" within the flights of the
screws. In addition,
depending on the composites manufacturing process, multiple feed screws may
also be
used.
Fig. 6 depicts a cross section of a screw 70 within a tube 71. It is important
to note
that the distance "D" between the screw outer diameter edge and the inner wall
of the
tube must be selected to prevent any shearing of the aggregates between the
screw and
the tube wall which could cause a lowering of the aggregate bulk density, and
subsequent
bridging of the aggregates. If the distance "D" is too small, the aggregates
will be
defiberized, yet if the distance "D" is too large, improper filling of the
screw will occur
and the material will not feed or feed rates will be lowered. Thus, a spiral
screw sized
correctly in relation to the tube inner diameter may be capable of conveying
the dense
aggregates without causing any bridging effect. The optimal distance "D"
depends on
the size of the aggregates being fed, however it is approximately equal to the
maximum
diameter or length of the aggregates.
FIG. 7 shows a side-view of a typical loss-in-weight screw feeder with
essential
components. Such a feeder is equipped with the described screw and tube 61
along with
a hopper 64, and a load cell 62 connected to motor and system controls 63. In
a loss-in-
weight feeder, the feed rate is controlled using the load-cell and system
controls to track
the reduction in weight of the dense aggregates within the hopper. As the feed
rates are
typically controlled by screw speed, this allows for dynamically adjustable
feed rates by
constantly varying screw speed with the rate in weight reduction. When the
hopper is at
a low-level of aggregates remaining, the system is re-fed while the feeder
temporarily
runs in "volumetric mode".
Under certain circumstances, such as when using feeder hoppers with dimensions
that are not favorable for material flow, an embodiment of the present
invention may
utilize a screw feeder with agitation. For the purpose of this invention,
agitation is
defined as a mechanism that continuously maintains the bulk of the dense
aggregates
within the feeder's hopper in motion. One example of agitation is a set of
rotating
"arms" 60, such as those shown in FIG. 6. It may be important to ensure that
the
agitation mechanism does not reduce density of the aggregates while they
reside in the
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feeder's hopper. Other forms of agitation such as vibrating hopper walls may
also be
used.
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EXAMPLE 1
In order to produce dense fibre aggregates from a lignocellulosic pulp bale, a
thermomechanical pulp bale with an approximate bale density of 0.8 g/cm3,
dimensions
of 60 cm x 80 cm x 54 cm, and bone-dry moisture content under 15% was fed into
a
Q100 Low-Speed High-Torque Shredder manufactured by SSI Shredding Systems
Inc., a
company having its place of business in Wilsonville, Oregon, USA. The system
was
equipped with a 2-inch cutter and a 1.5-inch screen and was running at
approximately 30
RPM. The Q100 system consists of 4 rotors and has a rated horsepower of 250-
300 hp.
Dense fibre aggregate production was performed without the optional hydraulic
ram, and
additional bales were continuously fed on top to maintain downward pressure.
If bales
were not fed to maintain continuous pressure, the bale currently being
processed
"floated" on top of the rotors once its weight had been reduced. The resulting
dense fibre
aggregates produced were of individual densities close to that of the original
bale density,
and had a bulk density of approximately 0.5 g/cm3.
Following production, the dense fibre aggregates were transferred without any
change in their density into the extension hopper of a DSR-Series loss-in-
weight screw
feeder manufactured by Brabender Technologie, a company having its offices in
Mississauga, Ontario, Canada. The screw feeder was equipped with a spiral
screw and an
agitation mechanism using a rotor within the hopper. The extension hopper
selected for
the feeder was rectangular and straight-walled to further minimize any
bridging effect.
The aggregates were fed without any bridging, and sufficiently filled the
screw. Both
batch and continuous feed modes were performed, and feed rates were achieved
that
matched the rated volumetric throughput of the feeder.
