WO1996036763A1

WO1996036763A1 - Pulping apparatus and related method for recycling paper

Info

Publication number: WO1996036763A1
Application number: PCT/US1996/006801
Authority: WO
Inventors: Larry D. Markham
Original assignee: International Paper Company
Priority date: 1995-05-18
Filing date: 1996-05-14
Publication date: 1996-11-21
Also published as: AU5744496A

Abstract

A pulping apparatus for mixing fibrous stock materials for recycling thereof, comprising a vessel having a passageway therethrough defined by an inlet (12) opening and an outlet opening. The vessel includes a rotatable axial shaft disposed in the passageway, and a series of cooperating propeller members being arranged in offset radial relation to effect continuous flow of the pulp slurry through the passageway of the vessel. The pulping vessel of the invention is designed to minimize breakdown of the ink, stickies and contaminants in wastepaper while at the same time providing sufficient mixing action to allow them to contact each other for agglomeration. The invention also includes related deinking processes employing the aforementioned apparatus.

Description

PULPING APPARATUS AND RELATED METHOD FOR RECYCLING PAPER

Field of Invention This invention generally relates to an improved apparatus and method for processing/repulping printed paper or paperboard. More particularly, it concerns an apparatus for mixing fibrous stock materials which permits formation of ink agglomerates within the apparatus without significant particle breakdown. Removal of the ink agglomerates produces a substantially ink free pulp medium which is used to make recycled paper and board products.

Background Art

Conventional agglomeration deinking processes have involved the mixing of agglomeration chemicals with wastepaper in a hydrapulper. Generally, typical conditions have been at 3-15% consistency and 50-70°C. The chemicals and the elevated temperature cause the ink particles and other contaminants to soften and to join with each other to form agglomerates which can then be removed by screening and cleaning techniques.

However, a major constraint on known agglomeration processes is that the action of the hydrapulper breaks the ink and contaminants into smaller particles, at the same time that agglomeration is forming larger particles. The apparatus of the present invention allows agglomeration to proceed without any particle breakdown, thereby permitting formation of larger agglomerates which are easier to remove from the pulp.

Typically, the high temperatures used in conventional agglomeration methods have both positive and negative effects. The ink softens and agglomerates better at high temperature, but the soft ink balls are also very easily broken down by mechanical attrition in the hydrapulper at high temperature. The apparatus and method of the present invention avoids breaking down the agglomerates, so that very high temperature can be used permitting the reduction or even the elimination of the addition of a deinking chemical. Various types of pulping and pulp mixing devices are known in art. U. S. Patent Nos. 4,964,733 and 4,861,165 to Fredriksson disclose methods and related apparatus for deinking printed paper slurries. The apparatus provides for hydrodynamic mixing of gases and particulate substances. Turbulence is created in the system by flowing the paper slurry through a passage having a series of alternating radially inwardly tapering conically shaped turbulence surfaces and radially outwardly flaring longer conically shaped turbulence surfaces. Deinking of the slurry is accomplished by introducing air into the ink fiber slurry, whereby air bubbles carry the ink particles to the surface to be removed.

U.S. Patent Nos. 4,360,402 and 4,231,526 to Ortner disclose flotation processes and related apparatus for deinking wastepaper. The wastepaper is repulped and passed through a sorting stage where fibers are separated via flotation procedures. A vibratory sorter is used to separate lightweight contaminants from the pulp slurry and a hydrocyclone is used to separate out heavy matter.

U.S. Patent No. 3,736,223 to Marsh discloses a process for recovering reusable paper fiber from garbage using hydraulic and mechanical shearing. U.S. Patent No.

2,916,412 to Altmann discloses a non-chemical method of deinking wastepaper. Revolving disc refiners are used to mechanically separate the ink particles from the pulp fibers. U.S. Patent No. 2,743,178 to Krodel discloses a process for deinking waste newspaper in which electrostatic charges are imparted to the ink particles and are separated from the cellulose fibers. These patents disclose deinking processes showing separation of contaminants by mechanical, non-chemical or electrostatic means.

Thus, known deinking apparatus and related processes are not entirely satisfactory in that complicated processes and high concentrations of expensive chemicals are necessary to obtain deinking. Further, adequate pulp cleanliness for use in recycled paper products is typically not achieved. There is a need in the art for apparatus and related processes which are less complex to produce a high- quality recycled paper. This invention is directed to the provision of such an apparatus and processes which have wide range applications in creating recycled paper with a high level of cleanliness, and using a low dosage of agglomeration chemical, if any.

Application of the apparatus of the invention in other types of deinking systems is also possible. Other deinking systems may use flotation, dispersion and washing procedures for ink removal. These systems are troubled by excessive attrition of contaminants prior to the screening operation. This problem is alleviated by the present invention.

Accordingly, it is a broad object of the invention to provide a pulping apparatus and related deinking process permitting the agglomeration of ink particles and contaminants from wood containing and wood free grades of paper using low pulping horsepower.

Another object of the invention is to provide a low cost agglomeration deinking process and apparatus that effectively and efficiently removes ink particles without using high concentrations of expensive agglomeration chemicals.

A still further object of the invention is to provide a recycled paper product having increased fiber strength due to the reduced attrition during pulping and a high level of cleanliness.

A more specific object of the invention is to improve the yield of the agglomeration deinking process by reducing the amount of paper fiber which is rejected from the process system in the screens and centrifugal cleaners.

Another object of the invention is to improve the removal of fine ink particles which normally must be removed in a washing process which entails substantial production of deinking sludge.

Another object of the invention is to increase the pulp brightness by removing the fine ink which reduces brightness, and thereby achieve a reduction in the requirement for expensive bleaching chemicals.

Disclosure of Invention

In the present invention, these purposes, as well as others which will be apparent below, are obtained by a new pulping apparatus for mixing fibrous stock materials comprising a vessel having a passageway therethrough defined by inlet and outlet openings and an agitating means for mixing the fibrous stock materials within the vessel to produce a pulp slurry. Propeller means housed within the vessel create a turbulent and continuous flow of the pulp slurry through the passageway of the vessel. The agitating means includes a rotatable axial shaft disposed in the passageway and the propeller means includes a series of cooperating propeller members which extend radially outward from the rotatable shaft, the propeller members being arranged in offset radial relation to effect continuous flow of the pulp slurry through the vessel.

The vessel is typically in a horizontal position but in another embodiment may be inclined at an angle up to 45° with the inlet side of the vessel lower than the outlet side.

The fibrous stock material may be treated with a deinking chemical prior to introduction to the vessel or the deinking agent may be introduced directly into the pulping vessel or into a liquid stream which recirculates through the vessel. Conditions and process parameters within the vessel permit mixture of the stock materials and the deinking chemical to allow for stable formation of ink agglomerates from ink and contaminant components. These ink agglomerates are removed from the pulp slurry by conventional screening and cleaning procedures to obtain a substantially ink free pulp medium.

The invention also includes related deinking processes employing the aforementioned apparatus. The apparatus and processes of the invention result in removal of substantial amounts of ink and contaminants, are effective for a wide range of fibrous materials and require reduced amounts of deinking chemicals, if any. Other objects, features and advantages of the present invention will be apparent when the detailed description of the preferred embodiments of the invention are considered in conjunction with the drawings, which should be construed in an illustrative and not limiting sense as follows:

Brief Description of the Drawings

FIG. 1 is a schematic illustration of the apparatus of the invention; FIG. 1A is an illustration of the agitating and propeller means of the apparatus of the invention;

FIG. IB is a schematic illustration of an inclined apparatus of the invention;

FIG. 2 is a diagrammatic view of the general process steps of the invention; FIG. 3 is a diagrammatic view of another embodiment of the process of the invention; and

FIG. 4 is a diagrammatic view of another embodiment of the process steps of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a pulping apparatus for mixing fibrous stock materials in accordance with the invention comprises a vessel 10 having a passageway therethrough defined by inlet 12 and outlet openings 14. The vessel includes agitating means for mixing the fibrous stock materials within said vessel to produce a pulp slurry and propeller means housed within said vessel for creating turbulent and continuous flow of the pulp slurry through said passageway. Referring to FIG. 1A the agitating means includes a rotatable axial shaft 16 disposed in said passageway, and said propeller means includes a series of cooperating propeller members 18 which extend radially outward from said rotatable shaft, said propeller members being arranged in offset radial relation to effect continuous flow of the pulp slurry through the passageway of the vessel.

The apparatus also includes a rotating means for continuous rotation of said axial shaft to create constant agitation. The pulping vessel preferentially has an elongated configuration. For use under atmospheric pressure the vessel has a flat top configuration with a U-shaped cross-section for mixing said fibrous stock materials with a removable cover for closure of the vessel. For use under pressurized conditions the vessel has a closed tubular configuration which prevents leakage from said vessel when mixing said fibrous stock materials. A steam header 20 with three injection nozzles may be present on the apparatus. The propeller members are typically flights and/or paddles selected from the group comprising solid helical flights, cut flights, cut and folded flights, paddle flights, variable pitch flights or variable diameter flights. The propeller members may also be radial arms having smooth and rounded edges to avoid formation of strings or other deposits from contaminants present in the wastepaper. Where the propeller members are paddles they are arranged at an angle to both convey and mix the fibrous stock materials. For propeller members which are cut and folded flights, the folds have a lifting action to mix the fibrous stock materials. Cut flights or variable diameter flights allow backmixing of the fibrous stock materials. In each instance all the propeller members are primarily large and rounded to avoid the formation of strings or other deposits from the contaminants.

The agitating means including propeller members can be driven by a variable speed motor, so that the amount of agitation of the wastepaper in the vessel can be adjusted to optimize the agglomeration. The speed of the shaft is low, less than 50 rpm, and preferably less than

20 rpm, resulting in a very low horsepower requirement.

Surprisingly, very low rpm is able to separate ink from the wastepaper and cause agglomeration of the ink, in contrast with conventional pulping devices for deinking which use large amounts of horsepower and high peripheral speed on the pulper rotor.

The pulping vessel of the invention is designed to minimize breakdown of ink, stickies and contaminants in wastepaper while at the same time providing sufficient mixing action to allow them to contact each other for agglomeration. Agglomeration occurs in the presence or absence of a deinking agent, depending on reaction conditions. In another embodiment of the apparatus, illustrated in Figure IB, the vessel is inclined at an angle of up to 45°, but preferably between 5-30°. A liquid level is maintained within the vessel for improved saturation of the wastepaper with the deinking chemical. A countercurrent flow of liquid through the vessel can also be maintained so the fine (unagglomerated) ink is washed back to the impregnation liquor tank until it is sufficiently agglomerated to be carried forward with the wastepaper or removed. The fibrous stock material may be treated with a deinking chemical prior to introduction to the vessel or the deinking agent may be introduced directly into the pulping vessel or into a liquid stream recirculating through the vessel. Conditions and process parameters within the vessel permit mixture of the stock materials and the deinking chemical to allow for stable formation of ink agglomerates from ink and contaminant components. These ink agglomerates are removed from the pulp slurry by conventional screening and cleaning procedures to obtain a substantially ink free pulp medium.

Preferably, if a deinking chemical is used, it is present at a dosage ranging from between 0.1 - 2.0% by weight calculated on the dry weight of the pulp used. Any deinking chemical capable of causing agglomeration of ink particles can be employed. Many of these agents are surfactants which make the ink hydrophobic and induce a tendency to agglomerate. For example, deinking agents such as Sansink PM-201 available from PPG Industries, Inc., Pittsburg, PA and BRD 2311 available from Buckman Laboratories, Memphis, Tennessee are suitable for use in the invention process. Agglomerating agents may also comprise polymeric materials which act as collectors to increase the size of the agglomerates such as the PX-101 by PPG Industries. Any of these agents or other similar commercially available deinking agents may be used in the present invention process. The process of agglomeration of ink particles has also been referred to as "aggregation", "densification", or "dispersion", and these terms are used interchangeably to describe the same process. (See J.K. Borchardt, Proceedings of TAPPI 1993 Pulping Conference, page 839) . The agglomeration chemical may be chosen to be suitable for the type of wastepaper being used.

FIGURES 2, 3 and 4 illustrate deinking processes utilizing the pulping apparatus of the invention. Typically, the fibrous material is agitated within said vessel for 3 to 120 minutes, at a pH in the range of 7 to 12 and a consistency of 3-40%. The agitation of the fibrous material causes dispersion of the paper fibers, ink and contaminant components to form a pulp slurry.

The vessel is maintained at temperatures above 30°C, preferably between 30-100°C. High temperatures of 50- 100°C are especially preferred because of the increased rates for both pulping and agglomeration, resulting in shorter retention times being required. Shorter retention results in less mechanical attrition on the ink and contaminants, so that increased ink and contaminant removal occurs in the screening and cleaning stages.

Referring to Figure 2, the printed wastepaper is shredded 22 and passed to the pulping apparatus 24, upon discharge the pulp slurry is passed through a detrasher 26 which separates a light reject and heavy reject stream as well as accepted pulp 30. The light rejects are processed through a trommel drum 28 with further accepted pulp combined with the previous accepts. The accepted pulp is then run through conventional screening and cleaning systems 32 to produce a substantially ink free pulp medium.

The detrasher 26 is equipped with a perforated extraction plate through which the large contaminants are not able to pass. Rotating arms or blades on the top of the extraction plate prevent the contaminants from plugging the extraction holes while the accepted pulp passes through the holes. The trommel drum 28 is a rotating perforated drum equipped with water showers to prevent plugging the holes with plastic and other contaminants. The contaminants which are rejected by the trommel have been effectively washed and dewatered in the trommel and are ready for disposal. In Figure 3, heated water containing the deinking chemicals is introduced near the upper end of the processor 24, which is preferably inclined, and washes the fine unagglomerated ink particles back to the inlet where they overflow into the impregnation liquor tank 40. Agitation in this tank causes agglomeration to occur at an increased rate, as does the introduction of agglomeration chemical, alkali and steam. The hot impregnation liquor containing agglomerated ink is then introduced, via pump 42, to the processor, and is the source of heat and deinking chemicals for pulping the wastepaper in the processor. Direct steam can also be used for heating the processor.

The larger agglomerated ink particles which are formed in the impregnation liquor tank and in the processor tend to be trapped in the fiber matrix of the pulp which exits the processor into the detrasher 26. The large ink particles therefore travel forward with the pulp into the screening and cleaning system, where they are readily removed because of their size. The fine ink particles are retained by the washing action in the inclined processor. This embodiment of the invention is especially preferred because it improves both the cleanliness and the brightness of the deinked pulp through the countercurrent washing action in the processor. Some of the liquor overflowing from the lower end of the processor can be sent to the sewer 44 or to a clarifier 46 to purge ash and pigment and pulp fines from the system, to increase the brightness and freeness of the deinked pulp. Bleach chemicals 48 can also be added to the recirculating liquor to increase the deinked pulp brightness. Flotation deinking can be used on the recirculating liquor to purge ink from the system.

The process illustrated in Figure 4 is similar to Figure 3. The "hot loop" water circuit is shown around the processor 24, whereas cooler water from the "cold loop" is used for diluting the pulp as it leaves the processor. The cooler water hardens the agglomerated ink, making it easier to remove especially in screening. The simplicity of the equipment used and the high amount of ink removal make the agglomeration deinking process of the invention advantageous over prior art practice. Further advantage of the pulping apparatus and process includes low attrition, low pulping horsepower, low deinking chemical usage, high cleanliness of the pulp, ability to handle very dirty wastepaper having a high stickies content and improved fiber strength of the resulting pulp.

Advantageously, the method of this invention for deinking printed paper is less complex than conventional deinking processes involving washing and flotation procedures.

It will be recognized by those skilled in the art that the invention has wide application in deinking a variety of printed paper to produce recycled paper.

Numerous modifications are possible in light of the above disclosure such as application of alternative agglomeration deinking chemicals chosen according to the wastepaper treated. In addition, alternative process parameters may be employed in the invention, which include using the deinking agent with no pH adjustment to the wastepaper; using the deinking agent in an alkali pH range; or using the deinking agent in the presence of other chemicals suitably employed in a deinking and/or papermaking process such as bleaching agents, defoamers, sizing ^• agents, brighteners, water quality processing agents among others. If desired chemicals can be added sequentially along the length of the pulping vessel.

Therefore, although the invention has been described with reference to certain preferred embodiments, it will be appreciated that other composite structures and processes for their fabrication may be devised, which are nevertheless within the scope and spirit of the invention as defined in the claims appended hereto.

Claims

1. An apparatus for mixing fibrous stock materials for recycling thereof, said apparatus comprising: a vessel having a passageway therethrough defined by inlet and outlet openings; agitating means for mixing the fibrous stock materials within said vessel to produce a pulp slurry; propeller means housed within said vessel for creating turbulent and continuous flow of said pulp slurry through said passageway; wherein said agitating means includes a rotatable axial shaft disposed in said passageway, and said propeller means includes a series of cooperating propeller members which extend radially outward from said rotatable shaft, said propeller members being arranged in offset radial relation to effect continuous flow of said pulp slurry through said passageway.

2. An apparatus according to Claim 1, further comprising a rotating means for continuous rotation of said axial shaft.

3. An apparatus according to Claim 1, further comprising means for removing contaminants from said pulp slurry.

4. An apparatus according to Claim 1, wherein said vessel has an elongated configuration.

5. An apparatus according to Claim 4, wherein said vessel has a flat top configuration with a U-shaped cross-section for mixing said fibrous stock materials under atmospheric pressure.

6. An apparatus according to Claim 4, wherein said vessel has a closed tubular configuration which prevents leakage from said vessel for mixing said fibrous stock materials under pressurized conditions.

7^'. An apparatus according to Claim 1, wherein said propeller members are rotated at a speed of less than 50 rpm.

8. An apparatus according to Claim 1, wherein said propeller members are radial arms having smooth and rounded edges to avoid formation of strings or other deposits from contaminants present in the wastepaper.

9. An apparatus according to Claim 1, wherein said propeller members are flights and/or paddles selected from the group comprising solid helical flights, cut flights, cut and folded flights, paddle flights, variable pitch flights or variable diameter flights.

10. An apparatus according to Claim 1, wherein said propeller members are paddles arranged at an angle to both convey and mix said fibrous stock materials.

11. An apparatus according to Claim 1, wherein said propeller members are cut and folded flights where the folds have a lifting action to mix said fibrous stock materials.

12. An apparatus according to Claim 1, wherein said propeller members are cut flights or variable diameter flights to allow backmixing of said fibrous stock materials.

13. An apparatus according to Claim 1, wherein said vessel is inclined at an angle of up to 45° with said inlet side of said vessel lower than said outlet side.

14. An apparatus according to Claim 1, wherein the fibrous stock material is mixed with an agglomeration deinking chemical and said agitating means effects mixture of said fibrous stock materials and said agglomeration deinking chemical to cause formation of ink agglomerates within said vessel to produce an ink-pulp slurry.

15. An apparatus according to Claim 14, wherein said propeller means creates a turbulent and continuous flow of said ink-pulp slurry through said passageway at a force which maintains the stability of said ink agglomerates.

16. An apparatus according to Claim 14, further comprising removal means for removing said ink agglomerates from said ink-pulp slurry.

17. A method for recycling fibrous stock materials comprising: introducing the fibrous materials into a vessel having a passageway therethrough defined by inlet and outlet openings; agitating the fibrous materials within said vessel to cause dispersion of paper fibers, ink and contaminant components to form a pulp slurry; propelling a turbulent and continuous flow of said pulp slurry through said passageway; wherein said agitation is produced by a rotatable axial shaft disposed in said passageway, and said propelling is produced by a series of cooperating propeller members which extend radially outward from said rotatable shaft, said propeller members being arranged in offset radial relation to effect continuous flow of said pulp slurry through said passageway; and removing ink and contaminant components from said pulp slurry to produce a substantially ink-free pulp medium.

18. The method according to Claim 17 wherein the fibrous material is agitated within said vessel for 3 to

120 minutes, at a pH in the range of 7 to 12 and a consistency of 3-40%.

19. The method according to Claim 17, wherein the fibrous stock material is mixed with an agglomeration deinking chemical to cause formation of ink agglomerates from ink and contaminant components.

20. The method according to Claim 19, wherein said turbulent and continuous flow has a force which maintains the stability of said ink agglomerates.

21. The method according to Claim 17, wherein said agitation is at temperatures above 30°C.

22. The method according to Claim 17, wherein said fibrous stock materials include paper, paperboard, printed paper, printed paperboard and contaminants.

23. The method according to Claim 17, wherein the fibrous stock material is mixed with a bleaching chemical.

24. The method according to Claim 17, wherein said agitation is produced by continuous rotation of said axial shaft .

25. The method according to Claim 17, wherein said vessel has an elongated flat top configuration with a U- shaped cross-section for agitating the fibrous stock materials under atmospheric pressure.

26. The method according to Claim 17, wherein said vessel has an elongated closed tubular configuration which prevents leakage from said vessel for agitating the fibrous stock materials under pressurized conditions.

27. The method according to Claim 17, wherein said propeller members are rotated at less than 50 rpm.

28. The method according to Claim 17, wherein said propeller members effect continuous flow of said pulp slurry through said passageway without any ink particle breakdown, where said members are flights and/or paddles selected from the group comprising solid helical flights, cut flights, cut and folded flights, paddle flights, variable pitch flights or variable diameter flights.

29. The method according to Claim 17, wherein said propeller members are paddles arranged at an angle to both convey and mix said fibrous stock materials.

30. The method according to Claim 17, wherein said propeller members are cut and folded flights where the folds have a lifting action to mix said fibrous stock materials.

31. The method according to Claim 17, wherein said propeller members are cut flights or variable diameter flights to allowbackmixing of said fibrous stock materials.

32. The method according to Claim 17, wherein said vessel is inclined at an angle of up to 45° with said inlet side of said vessel lower than said outlet side.

33. The method according to Claim 32, wherein a countercurrent flow of liquid containing fine ink is maintained through said vessel and mixed with said fibrous stock materials to form larger ink agglomerates.

34. A method for recycling fibrous stock materials comprising introducing the fibrous materials into the apparatus as defined in Claim 1 to produce an ink/pulp slurry and removing ink and contaminants from said slurry to produce a substantially ink free pulp medium.

35. A deinking apparatus for mixing fibrous stock material comprising: a vessel having a passageway therethrough defined by inlet and outlet openings; agitating means for mixing the fibrous stock materials within said vessel to produce an ink-pulp slurry; propeller means housed within said vessel for creating turbulent and continuous flow of said ink-pulp slurry through said passageway at a force which maintains the stability of ink agglomerates; wherein said agitating means includes a rotatable axial shaft disposed in said passageway, and said propeller means includes a series of cooperating propeller members which extend radially outward from said rotatable shaft, said propeller members being arranged in offset radial relation to effect continuous flow of said ink-pulp slurry through said passageway.

36. A deinking apparatus according to Claim 35, further comprising removal means for removing said ink agglomerates from said ink-pulp slurry.

37. A deinking apparatus according to Claim 35, wherein said vessel has an elongated configuration.

38. A deinking apparatus according to Claim 37, wherein said vessel has a flat top configuration with a U-shaped cross-section for mixing said fibrous stock materials under atmospheric pressure.

39. A deinking apparatus according to Claim 37, wherein said vessel has a closed tubular configuration which prevents leakage from said vessel for mixing said fibrous stock materials under pressurized conditions.

40. A deinking apparatus according to Claim 35, wherein said propeller members are flights and/or paddles selected from the group comprising solid helical flights, cut flights, cut and folded flights, paddle flights, variable pitch flights or variable diameter flights.