GB2161091A

GB2161091A - Process for the preparation of waste paper

Info

Publication number: GB2161091A
Application number: GB8516596A
Authority: GB
Inventors: Helmut Konecsny
Original assignee: JM Voith GmbH
Current assignee: JM Voith GmbH
Priority date: 1984-07-06
Filing date: 1985-07-01
Publication date: 1986-01-08
Also published as: FR2569432B1; AT389529B; ATA169785A; KR930003395B1; IT1185192B; CH668448A5; FR2569432A1; IT8521442A0; ES8608608A1; ES544895A0; GB8516596D0; KR860001247A; GB2161091B; JPS61108789A; DE3424919A1; DE3424919C2

Abstract

Waste paper is pulped in a pulper 1 and then fed to a screening apparatus in which a sieve (6,8) which is substantially perpendicular to the rotor axis separates a circulating space from an accepts region which is sub- divided into two compartments (7 and 9) which correspond to areas of the sieve having holes of different sizes, so that two accepts streams are obtained. The hole diameters differ by at least 5 mm, the smaller holes being within the range 2 to 8 mm. The rejects fraction is discharged intermittently through valve 16. The coarser accepts fraction may be recycled to the screening apparatus while pulper 1 is being filled, so that the screening apparatus works almost continuously. Alternatively the coarser accepts is fed to a second screening apparatus. (Fig. 2 not shown). <IMAGE>

Description

SPECIFICATION Process for the preparation of waste paper The invention relates to a waste paper preparation process and to a pulped waste paper screening apparatus. The invention is particularly, although not exclusively applicable to, or for use in a process for the preparation of waste paper in which immediately after the primary pulper operating at a high consistency setting-possibly with interconnection of a vat for buffering-the steeped and at least partially pulped waste paper is passed unsieved, that is to say with essentially all, or at least the large area soil fractions, into an apparatus which has a circulating space separated from an accepts portion, in which an impeller like rotor is rotatably arranged in front of an essentially planar sieve, and from which screening apparatus heavyweight soil is removed at its circumference of its substantially cylindrical housing in the downward direction via a large heavyweight soil take-off connecting piece when accepts material which contains all but a few fibres is withdrawable from the accepts portion or a rinsing of the housing is carried out by a soil take-off line. Such process is described in Papier, Carton et Cellulose, 1983, page 23.

With this process it is only possible to obtain a fibrous pulp freed from the coarsest impurities after the screening apparatus which is in a downstream position in the primary pulper. This is due to the fact that the sieve of the screening apparatus needs to have a fairly large hole size to prevent the apparatus from becoming blocked up all too rapidly as the primary pulper is emptied. In this way it is also only possible to operate the primary pulper discontinuously, as a result of which the dispersion of fibres is also only obtained batchwise after the screening apparatus. In this process, moreover, virtually the entire dispersion of fibres needs to be subsequently aftercleaned in screeners.

It is the object of the invention, while retaining the cleaning of the pulper from coarse soil, to prepare early on a pulp which is as clean as possible with comparatively little apparatus and without using an expensive screening drum.

According to one aspect of the present invention, a process for the preparation of waste paper comprises passing the at least partially pulped waste paper into a screening apparatus, the screening apparatus including a circulating space separated by a different sieve portion from two different areas, the hole sizes of one of the sieve portions being larger than that of the other sieve portion, the process including taking off substantially simultaneously fibre streams from each of the two different areas. The particular advantages of the process are realised in the course of the high-density pulping process in the primary pulper, since it is there that the biggest problem concerning the cleaning of the pulper arises, i.e normally a question how the coarse soil fractions are to be removed from the pulper.

According to another aspect of the present invention, a pulped waste paper screening apparatus includes a circulating space separated by a different sieve portion from two different take-off areas, the hole sizes of one of the sieve portions being larger than that of the other sieve portion.

In what follows, the invention will be explained by reference to an illustrative embodiment depicted in the drawing.

The Figure shows a schematic sketch of a primary pulper 1 from which a take-off line 2 leads without interconnection of a sieve directly to the inlet connecting piece 3 of the downstream screening apparatus 4. In said screening apparatus 4 there is provided a rotor 11 which rotates on a shaft 1 2 in a position in front of a planar sieve which consists of two portion 6 and 8 and which separates off accepts compartments 7 and 9 of an accepts portion 5 in the screening apparatus 4. The sieve portion 6 has a relatively fine perforation with a hole size which is less than 8 mm and the sieve portion 8 has a larger perforation with hole sizes up to 30 mm but certainly greater than 8 mm. The accepts compartments 7 and 9 are separated from each by a partition 18.The accepts compartment 7 is provided with a take-off connecting piece 13, as is the coarse fibre comparment 9 with a corresponding take-off connecting piece 1 4. At the take-off connecting piece 1 4 this fraction of the dispersion of fibres is passed by means of a pump 27 into an intermediate vat 20.

If then for example a consistency of 16% has been set in the pulper, the waste paper pulped into the form of a dispersion of fibres arrives due to the force of gravity at the inlet connecting piece 3 of the screening apparatus 4. In this apparatus the dispersion of fibres is diluted further in order to be screenable by the perforation of the sieve portions 6 and 8.

In this way a consistency of for example 4 to 6% can be present in the intermediate vat 20.

The diluting water is passed into the apparatus 4 by way of the connecting piece 1 9. In the accepts compartment 7 there is then a relatively clean accepts material which at least no longer has coarse impurities, so that said material needs only little after-cleaning. It is pumped by means of a pump 23 through line 29 to the further processing stage. The space in front of the sieve, that is to say the space in which the rotor 11 rotates, is then the site for the growing accumulation of coarse soil which could ultimately cause blocking of the sieve portions.

To prevent early blocking of the sieves, rinse water is passed into the apparatus by way of line 19, so that additional fibre portions can pass through the sieve portion 6 which has the finer perforation. Since at this stage a major foul content is still likely, it is preferable to close the slider 33 and open the slider 32, so that the dispersion of fibre which is then taken off can be conducted away separately by way of line 28. During this operation it is also possible to keep the slider 35 in the closed position for at least some of the time, for example at the start of this phase.

It is known from experience that after a certain time the water emerging from the connecting piece 1 3 or 14 no longer has a major fibre content. All the sliders which are situated in the lines downstream of the connecting piece 1 3 or 14 are then closed. It is then possible either to let the coarse soil still remaining in the housing drop into a waste trough by way of the coarse soil take-off connecting piece 1 5 and the slider 1 6 controlled by the actuating member 1 7 or to discharge the coarse soil by means of rinse water via the rinse connecting piece 24 while the slider 34 in line 25 is in the open position. This amount of coarse soil could then be additionally subjected to a concluding dewatering in order to recover the water.

During these rinse processes the pulper 1 can be refilled while the slider 30 is in the closed position and a new pulping process can start. During this pulping process, however, the apparatus 4 can continue to operate by introducing the dispersion of fibres accumulated in the intermediate vat 20 once more by means of pump 22 and via line 21 while the slider 31 is in the open position into the inlet connecting piece 30 of the apparatus 4.

Slider 26 is then closed and either slider 32 or 33, preferably slider 33, is opened, so that again relatively clean dispersion of fibres is obtained by sieve portion 6. It is necessary to take account here of the fact that the incompletely pulped waste paper is further divided by the additional pass through the apparatus 4 under the action of rotor 11 and this way the finer perforation of sieve portion 6 produces screenable fibre constituents.

This process sequence described in the preceding paragraph thus relates to the so-called discontinuous pulper operation. Although the pulper thus operates discontinuously, a largely continuous operation is achieved for the screening apparatus 4.

If the pulper 1 is operated continuously, the take-off of the dispersion of fibres therefrom needs to be interrupted only briefly for the rinsing processes taking place in the screening apparatus 4.

However, continuous pulpers generally operate at a lower consistency than 8% and have an accepts space separated by a screen from the pulping space, so that it is necessary to provide here a different switching arrangement for the screening apparatus 4, as is depicted in Fig. 2. It is necessary to add that preferably the hole sizes of the sieve portion 6 of the screening apparatus 4 which has the smaller perforation are between 2 and 5 mm, while the hole size of the sieve portion 8 which has the coarser perforation is not smaller than 10 mm, preferably 20 mm.

The accepts compartments can also be, in an arrangement different from that depicted, concentric to each other. The sieve portion or area 6 which has the finer perforation is advantageously larger than the other by a sufficient amount as to permit a throughput which is at least 100% to 150% greater than that of the other sieve portion.

Fig. 2 depicts a process variant with a continuously operated pulper in horizontal construction. In this Figure, such components and lines as correspond to Fig. 1 are identified by the same numerals as in Fig. 1, except for an additional apostrophe.

In this procedure, a large portion of the dispersion of fibres is withdrawn at pulp consistencies of around 8% from the pulper 1' via sieve 36 through line 38 and is introduced into a secondary pulper 39. The perforation of the sieve of pulper 1' preferably has a hole size of 1 8 mm. This operating method is known from US Patent 4,017,033. In the case of these secondary pulpers, a sieve separates as indicated a circulating and pulping space 14 from an accepts space 41. An impellerlike rotor 42 is arranged to be rotatable close to the sieve. The perforation of the sieve in the secondary pulper preferably has a hole size between 3 and 5 mm. The accepts material is passed from the accepts space 41 by way of line 46 to a discharge vat 47.Two pulp flows enriched in impurities are withdrawn from the pulping space 40, namely via line 43 a pulp flow which is particularly enriched in lightweight soil and via line 44 a pulp flow which is particularly enriched in heavyweight soil. The heavyweight soil pulp flow is preferably given an intermediate cleaning in a hydrocyclone 49. The two pulp flows are collected in a vat before their further purification.

A soil-enriched fraction is withdrawn from the primary pulper 1' via line 2' with the slider 30' in the open position and is introduced into the screening apparatus 4', which corresponds to the screening apparatus 4 of Fig. 1. The accepts material withdrawn from the accepts compartment with the greater degree of soiling owing to the coarser perforation of the upstream sieve portion is in this case introduced into the accepts take-off line 38 of the primary pulper 1. The accepts material which is relatively cleaner owing to the finer perforation of the upstream sieve portion likewise passes into the discharge vat 47 via line 29'. Using this process, the coarse contaminations are removed from the primary pulper 1' quasi continuously, since as part of the dispersion of fibres arriving in line 2' they are screened out by the screening apparatus 4' and separated off. The Figure shows that the take-off line 2' passing into the screening apparatus 4' is preferably connected to the top-end take-off pipe 37 of the horizontally constructed primary pulper 1'. This way of connecting the line 2' is known per se from US Patent 3,989,197. The hole sizes of the sieve portions in the screening apparatus 4' are likewise preferably between 2 and 5 mm in the case of the finer perforation and between 10 and 30 mm, in particular 20 mm, in the case of the coarser perforation.

It is evident that the circulating space 50 (as also in the case of Fig. 1) of this screening apparatus 4 is reduced in size at its inlet end by 10-25% of its diameter to form an inlet space and thus improved accumulation of even coarse or heavyweight soil is obtained at the very capaciously constructed take-off connecting pieces 15' (or 15).

Claims

1. A process for the preparation of waste paper comprising passing the at least partially pulped waste paper into a screening apparatus, the screening apparatus including a circulating space separated by a different sieve portion from two different accepts areas, the hole sizes of one of the sieve portions being parger than that of the other sieve portion, the process including taking off substantially simultaneously fibre streams from each of the two different accepts areas.

2. A process as claimed in Claim 1 comprising periodically removing heavyweight soil from the screening apparatus, upstream of the sieve portions, each time prior to repeatedly passing the at least partially pulped waste paper into the screening apparatus and taking off the fibre streams from each of the two different accepts areas.

3. A process as claimed in Claim 1 or 2 in which the fibre stream which has been taken off from the accepts area associated with the sieve portion with the larger hole sizes is again screened in the screening apparatus.

4. A process as claimed in Claim 3 comprising screening again the fibre stream which formerly had been taken off from the area associated with the sieve portion with the larger hole sizes in the screening apparatus while stopping the extraction of suspension out of the accepts area associated with the sieve or sieve sections with the larger holes.

5. Process for the preparation of waste paper in which immediately after the primary pulper operating at a high consistency setting-possibly with interconnection of a vat for buffering-the steeped and at least partially pulped waste paper is passed unsieved, that is to say with essentially all or at least the largearea soil (or reject) fractions, into an apparatus which has a circulating space separated from an accepts portion, in which an impellerlike rotor is rotatably arranged in front of an essentially planar sieve, and from which screening apparatus heavyweight soil is removed at its circumference of its substantially cylindrical housing in the downward direction via a large heavyweight soil take-off connecting piece when accepts material which contains all but a few fibres is withdrawable from the accepts portion or a rinsing of the housing is carried out by a soil-take off line, characterised in that within the period after the operations mentioned at least predominantly simultaneously two different fibre streams are taken off via two different areas of the sieve or sieve portions of the screening apparatus which have two differently sized perforations, the hole sizes of which differ by at least 6 mm, from the accepts potion of the screening apparatus, the steps being periodically repeated.

6. Process according to Claim 5, characterised in that in the case of discontinuous operation of the primary pulper and after emptying thereof or in the case of the sieve of the screening apparatus being blocked with prevention of the take-off pulp from the accepts compartment downstream of the sieve portion with the coarser perforation the amount of fibrous material accumulated in a vat and initially withdrawn from this accepts compartment is again screened in the screening apparatus.

7. A process for the preparation of waste paper substantially as herein described with reference to, and as shown in Figs. 1 or 2 of the accompanying drawings.

8. A pulped waste paper screening apparatus including a circulating space separated by a different sieve portion from two different take-off areas, the hole sizes of one of the sieve portions being larger than that of the other sieve portion.

9. Apparatus as claimed in Claim 8 in which the area of each hole in the sieve portion with the larger hole sizes is generally 200% or more greater than the area of the holes in the other sieve portion.

1 0. Apparatus as claimed in Claim 8 or 9 in which sizes of the holes in the sieve portions differ by at least 6 mm.

11. Apparatus as claimed in any of Claims 8, 9 or 10 in which the hole size in one sieve portion is less than 8 mm and the hole size in the other sieve portion is 10 mm or more.

1 2. Apparatus as claimed in Claim 11 in which the hole sizes in one sieve portion are between 2 and 5 mm, and the hole sizes in the other sieve portion are between 10 and 30 mm.

13. Apparatus as claimed any of Claims 8 to 1 2 in which the circulating space includes an inlet which is reduced in size by 10-25% of the diameter of main circulating space.

14. Apparatus as claimed in any of Claims 8 to 1 3 in which one of the sieve portions surrounds the other.

1 5. Apparatus as claimed in any of Claims 8 to 14 in which the sieve portions are concentric to each other.

1 6. Apparatus as claimed in any of Claims 8 to 1 5 in which the configuration of the sieve portions is such that the pulp stream through the sieve portion with larger holes is less than that through the other sieve portion.

1 7. Apparatus as claimed in Claim 1 6 in which the flow streams through the sieve portions are in the general ratio of 1:2 or more.

1 8. A pulped waste paper screening apparatus substantially as herein described with reference to, and as shown in Figs. 1 or 2 of the accompanying drawings.

1 9. Apparatus as claimed in any of Claims 8 to 18 when used in a process as claimed in any of Claims 1 to 7.

20. Means for carrying out the process, characterised in that the screening apparatus is constructed with a front-end inlet into the circulating space, opposite of which are arranged the impeller wheel and adjacent thereto the sieve which separates the circulating space from the accepts portion of the apparatus and which has two portions or areas the perforations of which differ in hole size by more than 6 mm, the smaller hole size being less than 8 mm, preferably between 2 and 5 mm, and the larger hole size being between 10 mm and 30 mm, and each sieve portion is associated with an accepts compartment.

21. Means according to Claim 20, characterised in that the accepts compartments are concentric to each other.

22. Means according to Claim 20 or 21, characterised in that the sieve portion or area which has the finer perforation is larger than the other by an amount such that the pulp streams withdrawn through the two sieve portions are in a ratio of at least, for example, 2:1.

23. Means according to any of Claims 1 9 to 21, characterised in that the supply line for the dispersion is connected to a central frontend inlet space of the screening apparatus the diameter of which is about 10-25% smaller than the maximum diameter of the adjoining circulating space of the screening apparatus.