CA1078557A

CA1078557A - Method and apparatus for recovering fibres from fibrous material

Info

Publication number: CA1078557A
Application number: CA238,481A
Authority: CA
Inventors: Sven-Olof Sandberg; Frey V. Sundman
Original assignee: Ahlstrom Corp; Munksjo AB
Current assignee: Ahlstrom Corp; Munksjo AB
Priority date: 1974-11-07
Filing date: 1975-10-28
Publication date: 1980-06-03
Also published as: NO146645C; CH612707A5; BR7507269A; GB1525947A; DE2547896A1; DE2547896B2; NO146645B; JPS5172606A; AT351351B; IT1048768B; NL7512582A; NO753710L; FR2290532B1; JPS553476B2; ATA817575A; FR2290532A1; AU8612375A; DE2547896C3

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.

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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107BS5'7 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 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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~785~7 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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, . ' ~78~57 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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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 _ g _ '~
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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 . . .

~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 ; ~9 '.
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~0785S7 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 ~:i .~, .. ..

~7~35S7 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 .........

. . ' , ~ ' ~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 ~C~7BSS7 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 ~,.~1, . .~ . . . ~ .
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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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~L~78SS7 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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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.

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.

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 and 30, wherein D is the diameter of said drum expressed in meters.

9. The method of claim 8 wherein the rotational speed is 28.

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 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.