METHOD AND APPARATUS FOR RECOVERING FIBRES FROM FIBROUS MATERIAL

PROCEDE ET APPAREIL DE SEPARATION DES FIBRES D'UNE MATIERE FIBREUSE

English Abstract

Abstract of the Disclosure
A method and an apparatus to recover cellulose
fibres from fibrous material by treating it in a rotating
drum together with a dissolving liquid, in which drum
the material is made to repeatedly impinge on the drum
jacket face, whereby the fibrous material is divided
into a fine fraction which is drained off through
apertures formed in the drum jacket surfaces, and a
coarse fraction which is removed through an opening
formed in the drum end wall opposite the material
supply end of the drum. The method and the apparatus
make possible to re-use in an efficient and economical
manner unsorted waste paper and returns which may contain
plastics, foils and metal objects and other foreign
matter which thus remain inside the drum when the
liquid together with the desintegrated fibres are
drained off, and which may then be conveniently
removed from the drum.
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Claims

WHAT IS CLAIMED IS:
1. An improved method of recovering fibres
from fibrous material by introducing said material
into a rotating drum, said drum having lifting means
therein, and dividing said fibrous material in said
drum into particles of varying sizes, characterized
by disintegrating said fibrous material in wet
condition by rotating said drum at a speed sufficient
to ensure that said fibrous material is lifted inside
said drum in the rotational direction thereof with
the aid of said lifting means and is impinged against
the lower portion of the drum jacket prior to
returning to the bottom of the drum whereby said
fibrous material is divided into a fine fibrous
fraction and a coarse fibrous fraction, and draining
off said fine fraction through apertures formed in
the jacket of said drum and removing said coarse
fraction through an opening formed in one end wall
of the said drum.
2. An improved method according to claim 1,
wherein said fibrous material consists of waste paper
from which fibres are to be removed, the method
comprising performing the dissolving stage, i.e.
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desintegration of the fibre bonds, by using an alkaline
liquid, said alkaline liquid preferably containing
a surface-tension reducing agent.
3. An improved method according to claim 2,
comprising using a liquid made alkaline through the
addition of sodium hydroxide, and using black
liquor as said surface-tension reducing agent.
4. A method as described in claim 1 wherein said
fibrous material is peat, comprising transforming said
peat into a pumpable suspension through treatment
thereof in said drum together with water which is added
when the dry contents of said peat exceeds 10%.
5. An improved method according to claim 1,
comprising removing the pith cells from bagasse by
treating said bagasse in said drum, said treatment
comprising two steps, a first step including the use
of circulating water and a second step including the use
of rinsing water.
6. An improved method according to claim 1,
comprising returning a portion of the wetting liquid
containing dissolved fibrous material to said drum.
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7. An improved method according to claim 1,
comprising supplying said fibrous material continuously
to said drum and discharging said coarse material
continuously from said drum.
8. An improved method as claimed in claim 1,
comprising driving said drum at a rotational speed of
between 25<IMG> and 30<IMG>, wherein D is the diameter
of said drum expressed in meters.
9. The method of claim 8 wherein the rotational
speed is 28<IMG>.
10. An improved method as claimed in claim 1
wherein said lifting means are arranged to exert in
axially directed force on the material in the drum.
11. An improved method as claimed in claim 1
wherein said lifting means are lengthwise internal
ribs.
12. An apparatus to perform the method according
to claim 1 for recovery of fibres from a fibrous
material by dissolving said material in a liquid,
said apparatus comprising a rotating drum in a
horizontal or tilted from horizontal position having
a perforated jacket surface, ribs provided inside said
drum so as to extend essentially in the longitudinal
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direction of said drum, said ribs serving as lifting
means for lifting said fibrous material to a level
from which said material falls from said ribs and
impinges upon said jacket, a tube conduit supplying
defibrating and dissolving liquid into said drum.
13. The apparatus according to claim 9, comprising
a first opening formed in one end wall of said drum,
said fibrous material supplied through said opening,
and a second opening formed in the opposite end wall
of said drum, said coarse fraction removed from said
second opening.
14. The apparatus according to claim 9, comprising
said lifting means divided into sections, said
sections displaced relative to one another in the
circumferential direction of said drum.
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Description

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11D'78S57
The present invention concerns a method of re-
covering fibres from fibrous materials such as waste
paper, peat and bagasse, and an apparatus adapted to
perform the method. The method and the apparatus are
particularly intended to handle unsorted fibrous
materials containing foreign matter such as e.g. waste
paper and returns containing plastics-coated wrapping
material.
BACKGROUND OF THE INVENTION
The mounting consumption of paper has increased the
need for re-use of waste paper and returns as the raw
material in the manufacture of paper and cardboard
materials. One of the difficulties in making use of
this raw material is its heterogenous condition.
Unsorted waste paper may contain paper having a
high wet strength, paper that may only be disintegrated
with great difficulty, foils, metal strings, threads
and other particles that have to be removed. In connection
with the collection of waste paper foreign matter may
be separated but some of the foreign matter and
pollutants may be separated only in connection with
the desintegration and defibration of the waste paper
or during a later stage of the treatment.
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PRIOR ART
To desintegrate and defibrate waste paper a pulper
has hitherto been used, i.e. an apparatus consisting
of a trough wherein a winged rotating impeller wheel
sets into motion the liquid wherein the defibration
takes place. The waste paper is defibrated in a pulper
in the following manner: -
Owing to the effect of the suction created by the
impeller wheel the material flows towards the impeller
wheel centre. When the material moves towards the
wheel periphery, it is exposed to impacts from the wings
of the rotating impeller wheel and thus is shredded
into pieces.
The paper pieces are thrown away from the impeller
- 15 wheel at a high speed, As a result of the difference in
speed between the material thrown away from the
impeller wheel and the environmental medium the paper
p1eces are exposed to frictional forces which detach
the fibres.
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To achieve complete defibration in a pulper
operating in accordance with the principle outlined
above, it is necessary to expose the waste paper to
a lengthy treatment. Desintegration usually is carried
out at a concentration of 2 - 3%, for which reason the
amount of liquid circulating inside the pulper is
considerable and the required power consequently high.
Usually, the defibration therefore cannot be completed
with the aid of the pulper but may be carried out only
to a degree which is sufficient to obtain a pumpable
pulp which is led to the desintegrator in which the
defibration is completed.
The method hitherto used to desintegrate waste
paper, i.e. with the aid of a pulper, suffers from
certain disadvantages. When treating unsorted waste
paper containing e.g. plastics-coated paper, the flow
of material fed to the desintegrator will contain
pieces of paper which are not completely desintegrated
and from which the plastics material has not been
removed. The plastics material is shredded into small
pieces in the desintegrator and these pieces are
difficult to remove from the system in subsequent
stages of the process. The waste paper is exposed
to tearing effects in the pulper, whereby the fibres
are destroyed. In a pulper which works in a continuous
manner, it is difficult to remove all foreign matter
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713S57
separated therein. The screen of the pulper is provided
with comparatively large openings, in the order of
between 6 and 25 millimetres, and consequently paper
clips and other metal objects may pass through.
SUMMARY OF THE INV~NTION
In accordance with the invention the cellulose
material is defibrated in a rotating drum having a
perforated jacket and provided on its inner surface
with ribs extending essentially in the longitudinal
direction of the drum, said ribs setting the material
fed into the drum in motion in a manner to be
described in the following. The invention is applicable
to treatment of the cellulose material both in a
continuous manner and in batches.
Upon rotation of the drum the material fed
thereinto takes part in the drum rotation and is
lifted by the drum ribs to a level above the drum
centre axis from which level the material falls down
to the lowest point of the drum jacket. By choosing
the rotational frequency of the drum in a suitable
manner relative to the drum diameter it is possible
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to bring the material along to a position close to
the highest point of the drum. Liquid necessary for
the defibration of the cellulose material is supplied
continuously to the drum interior and surplus liquid
is drained off through the perforations made in the
drum jacket. When the cellulose material has been fed
into the drum it is first submitted to a wetting phase.
When the cellulose material, soaked through, falls
down and impinges against the lower part of the drum
jacket the fibre bonds are destroyed but foreign matter
remains intact. Detached fibres and fibre clusters which
may pass through the perforations in the drum jacket
are drained off therethrough together with the
defibration liquid, down into a tank positioned below
the drum.
In accordance with the method of the present
invention the waste paper is defibrated in a manner
permitting separation of foreign matter before the
fibrous material is led to a desintegrator for further
defibration. As a result, it becomes possible, with-
out previous sorting, to make use of waste paper,
containing e.g. plastics-coated wrapping and packaging
materials.
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Thus, the invention is defined in its broad
aspect as an improved method of recovering fibres
from fibrous material by introducing said material
into a rotating drum, said drum having lifting means
therein, and dividing said fibrous material in said
drum into particles of varying sizes, characterized
by disintegrating said fibrous material in wet
condition by rotating said drum at a speed sufficient
to ensure that said fibrous material is lifted inside
said drum in the rotational direction thereof with the
aid of said lifting means and is impinged against
the lower portion of the drum jacket prior to returning
to the bottom of the drum, whereby said fibrous
material is divided into a fine fibrous fraction and
a coarse fibrous fraction, and draining off said fine
fraction through apertures formed in the jacket of
said drum and removing said coarse fraction through
an opening formed in one end wall of said drum.
In a further embodiment there is provided an
apparatus for the carrying out of the above method,
the apparatus comprising a rotating drum, having a
perforated jacket surface, ribs provided inside
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35S~
said drum so as to e~tend essentially in the
longitudinal direction of said drum, said ribs
serving as lifting means for lifting said fibrous
material to a level from which said material falls
from said ribs and impinges upon said jacket, a tube
conduit supplying defibrating and dissolving liquid
into said drum.
The invention may be carried out either continously
or in batches.
Peat collected from bogs, contains between 85 and
95% of water as well as stones, roots and root parts.
To convert peat to pumpable form it has hitherto
been customary to dissolve it in a pulper, wherein
it is diluted into a suspension the dry contents of
which are less that 5%, whereafter the suspension is
later dewatered. As it is difficult to dewater peat,
it is desirable that water is added in amounts as
small as possible. In order that the rotor of the
pulper does not break, the peat must be subjected to
coarse (primary) sorting before its desintegration.
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1~'78557
One has found that the desintegration of wet peat
and the separation of the dry substance from the coarse
particles may be performed with extreme e~ficiency and
without subjecting the peat to a primary sorting, if
it is treated in a rotating, perforated drum. If the
peat dry contents exceeds 10%, liquid is added to
dilute it. During the treatment in the drum, the
solid structure of the peat is desintegrated, and the
detached peat is drawn off through the apertures in
the drum jacket, whereas stones, roots and root parts
remain and may be removed at the drum end. A pumpable
pulp thus is obtained the dry contents of which
amount to 10~.
Bagasse which is obtained as a residue product
after extraction and pressing-out of the sugar -
contents from sugar canes may also be used to produce
cellulose. Bagasse contains about two thirds of
fibres (as calculated on the dry substance) which are
suitable for use in the cellulose manufacture, and
about one third of pith cells which are unsuitable for
this purpose. To remove the pith cells which are
present mainly in the sugar cane stem centre, the bagasse
has hitherto been treated in machines that require
considerable amounts of energy, such as hammer mills
or pulpers. One has found, however, that the separation
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~078~iS7
of the cellulose cells from the pith cells may be
carried ou-t with surprising ease in a rotating drum
having a perforated jacket. The pith cells which are
short are flushed through the drum apertures together
with the water, and the cellulose fibres may be removed
in the shape of sticks at the drum end. In the drum,
the epidermis cells are likewise scraped off and form
a waxy surface layer on the stems which is detrimental
to the cellulose manufacture.
The rinsing liquid is preferably circulated and
drained off when it contains between 2 and 4~ of pith
cells, etc. The cellulose fibres are removed when they
have a dry content of between 15 and 20~. The
bagasse preferably is cut into small lengths and
crushed before its treatment in the drum.
BRIEF DESCRIPTION OF THE DRAWINGS
. _
Some embodiments of the invention will be described
more in detail in the following with reference to
the accompanying drawings, wherein
Figs. l, 2, 3, 4, and 5 illustrate one embodiment
of the invention intended for continuous operation.
More precisely, Fig. l is a schematic representation
of a process utilizing the method and the apparatus in
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~07~3557
accordance with the inventor,
Fig. 2 is a sectional view along line A-A of
Fig. l, and Figs. 3, 4, and 5 are views illustrating
the structure of the apparatus more in detail.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In Figs. l and 2 the dissolving drum is designated
by numeral reference l, its end walls by numerals
2 and 3 and its jacket by numeral 4. The cellulose
material is supplied by means of conveyor 5 and is
allowed to slide down a chute 6 into the drum through
an opening in the end wall 2. The drum is provided
with longitudinally extending, internal ribs 7 which
continuously feed material from the lower portion of
the drum jacket to a higher level, from whence the
material falls downwards. Defibration liquid, possibly
having necessary chemicals added thereto, is supplied
through an injection tube 8. In the case of waste
paper, it is preferred that the liquid be an alkaline
liquid containing a surface-tension reducing agent.
Preferably the liquid is made alkaline through the
addition of sodium hydroxide and utilizes black liquor
as the surface tension reducing agent. Fibre material
which has been defibrated (detached) in the drum, flows
together with liquid downwards into a tank 9 from
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whence part of the fibrous suspension thus ~ormed is
carried back into the drum through a pipe line 10 which
is connected to the injection tube 8. A portion of
the liquid is pumped further to a sorter apparatus 11
wherein coarse and heavy particles are removed.
In a desintegrator 12 a defibration operation there-
after is effected to allow fibreclusters, if any, to
dissolve. The fibre suspension is washed and
thickened in a filter 13, to which wash water 14 is
added and from which liquid is led back to the drum
via a conduit 15 and to a drainage via a conduit 16.
The fibre material is removed from the filter, where-
upon it may be further cleaned for subsequent use.
Heavy material forms a sedimentation inside the
tank 9 and may be removed therefrom by means of a
screw conveyor 17 disposed in the tank bottom. In the
drum, the fibres aré separated from ~oreign matter
which is removed from an opening in the end wall 3.
When the cellulose material has been fed into the
drum, it takes a certain time, such as e.g. 1 to Z
minutes, before the material has absorbed moisture and
the defibration stage proper starts. For this reason
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it might be preferable to form the jacket section
at the paper supply end of the drum continuous, i.e.
non-perforated. The non-perforated section of the
drum jacket is designated by numeral 18 in the drawings.
The defibration efficiency of the drum is dependent
on the drum diameter. The larger the drum, the higher
the vertical drop, resulting in an increased desintegrating
effect when the cellulose material impinges on the
drum surface. A suitable diameter size is 2 to 3 meters.
The rotational speed of the drum should be between
25 ~ and 30 ~ , wherein D represents the diameter
of the drum expressed in meters, and preferably 28 ~ ---,
in order to obtain the maximum lifting power.
The lifting means may either be integral, in one
piece, and extend from one end of the drum to the
opposite one, or else comprise a number of sections
which are positioned in displaced relationship in the
circumferential direction of the drum, the arrangement
preferably being such that the section closest to the
supply end of the material is positioned at the front
relative to the rotational direction, each subse~uent
section being positioned at a certain distance behind
the preceding one. To improve the efficiency of advance-
ment of the material, the lifting means could be
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~78S57
arranged at an angle to khe rotational axis of the
drum. Alternatively, the drum may be disposed in a
tilted position. It is also possible to advance the
material while using flushing liquid.
Fig. 3 is a longitudinal section through a drum
arranged to treat cellulose material. Fig. 4 illustrates
the drum as seen in the direction towards the supply
end thereof. Fig. 5 illustrates a cross-sectional view
along line B-B in Fig. 3. In Figs. 3, 4, and 5 are
used partly the same numeral references as in Figs. 1
and 2. The internal ribs 7 serving as lifting means
are slightly screw-shaped, i.e. their direction of
extension deviates somewhat from the longitudinal exten-
sion of the drum. The tilting angle preferably is
between 2 and 10. secause the end of the lifting means
closest to the end wall 2 through which the cellulose
material is supplied, is positioned at the front as seen
in the direction of feed, the lifting means exert an
axially directed force on the material, which force
advances the material forwards in the direction towards
the opposite end wall 2. The drum is supported at each
end by two rotatably mounted rollers 19. The drum is
driven by a motor 20 by means of a drive chain 21 and
chain wheels 22 and 23. Separated, coarse material is
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removed by scoops 24, lifting the material from the
lower portion of the drum jacket into a chute positioned
adjacent the opening in the end wall 3.
Example 1
7,5 kg magazine paper and smaller amounts of
plastics-coated packaging material, aluminum foil,
textile products, leather, capsules and book covers
were placed in a closed drum having a diameter of
1 meter and a length of 0,5 meters, exhibiting on its
inner face 8 internal ribs extending in the longi-
tudinal direction of the drum and having a height of
15 centimeters. The drum jacket was perforated with
apertures having a diameter of 5 millimetres, with
a total aperture area of 40% of the jacket surface.
The drum was driven at a rotational speed of 25
revolutions per minute. 330 litres of water to which
was added 200 grams NaOH and 100 grams black liquor
was circulated through the drum at a flow rate of
125 litres/minute. The liquid temperature was between
45 and 50C. After 8 minutes the drum was opened and it
was found that all magazine paper had been defibrated and
drained off together with the circulating liquid. The
paper of the packaging material had been defibrated but
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1~7~35S7
the plastics material remained inside the drum without
having been shredded. The aluminium foil, the textile
material and other foreign matter remained inside the
drum. The book covers were partly dissolved.
Example 2
For the treatment of waste paper at a capacity of
100 tons in 24 hours, containing essentially magazine
and ordinary newsprint paper the drum should have the
following dimensions and technical data:-
Diameter 2.5 meters
Length 10 meters
Length of perforated section 9 meters
Aperture diameter 5 millimeters
Aperture area 20~
Frequency of rotation 15 r/min
Effect 50 kW
The fibre concentration in the tank is 2 - 3% and
following the filter 10 - 12~.
The defibration liquid is to consist of water having
an alkali added thereto, such as NaOH, to dissolve the
binding agents of the printing ink and~the coating
substances, and also some surface-active addition, such
as black liquor, tall soft soap or other commercially
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available wetting agents in order -to allow water to
penetrate into the paper.
The defibration operation occurs ef~iciently
already at a comparatively low temperature, such as
between 40 and 60C.
Example 3
50 kg of peat containing 10% dry contents was
treated during 5 minutes in a rotating drum as in the
Example 1. When the drum was opened it could be
established that 0.5 kg of stones, roots and root parts
remained inside the drum.
The tank beneath the drum contained the major
portion of the dry contents in the form of pumpable
suspension containing approximately 8% of peat. No
diluting liquid had been added.
Example 4
15 kg of bagasse having a dry contents of 50~ and
which had previously been pre-treated in a manner not
described more in detail but during which the content
of pith cells had been reduced to 25%, were treated
in a rotating drum in accordance with the examples
described above. The treatment was carried out in two
steps. In the first step, the drum was rotated for
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10 minutes, during which time 300 liters of circulatingwater were passed through the bagasse. In the second
step, the water was exchanged by an equal amount of
circulating rinsing water which was allowed to flow
through the bagasse during further rotation of the
drum during 5 minutes. When the drum was opened it
was found that approximately 80% of the dry substance
remained inside the drum and that the contents of pith
cells had been reduced to approximately 10%, which is
a very satisfactory result.
Also the use of the drum for barking of low-grade
timber and twigs falls within the scope of the present
invention, as does also the use thereof for the
desintegration of undissolved wood-chips and separation
of the knots in paper pulp after digestion.
The size of the apertures in the drum jacket should
be adjusted to fit the desired sorting grade. Suitable
sizes of waste paper, peat and bagasse are respectively
4 - 6, 8 - 15, and 3 - 5 millimetres. The embodiments
of the invention in which an exclusive property or
privilege is claimed are defined as follows:-
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