DE102008009134A1 - Removing impurities from aqueous fibrous material suspension formed from printed waste paper, comprises forming fine fraction and rough fraction from the material suspension by fractionating, and treating the fine fraction in a floatation - Google Patents

Abstract

The method comprises forming a fine fraction (F) and a rough fraction (G) from an aqueous fibrous material suspension by a fractionation (2), treating the fine fraction in a floatation (1), which is the first floatation in the processing progress of the method, dispersing and floating the rough fraction and then subjecting to a further fractionation (3), in which the fine fraction and the rough fraction are formed, and again dispersing the rough fraction of the further fractionation. The further fractionation is a washing. The fine fraction is enriched with fine materials. The method comprises forming a fine fraction (F) and a rough fraction (G) from an aqueous fibrous material suspension by a fractionation (2), treating the fine fraction in a floatation (1), which is the first floatation in the processing progress of the method, dispersing and floating the rough fraction and then subjecting to a further fractionation (3), in which the fine fraction and the rough fraction are formed, and again dispersing the rough fraction of the further fractionation. The further fractionation is a washing. The fine fraction is enriched with fine materials during the fractionation and the rough fraction is enriched with short- and long fibers. The rough fraction of the further fractionation is treated in a further floatation (10) after further dispersion (8). A part of the fine fraction of the further fractionation is guided in the further floatation. The solids of a part of the fine fraction are removed. The distribution of the fine fraction is adjusted for regulating the quality of the fibrous material and the yield of the process. The selective floatation processing of the fine fraction and a part of the dispersed rough fraction is the first selective floatation in the processing progress of the method. The selective floatation is carried out with a consistency of 1.0-2%. The dispersion is carried out in a disk disperger and a kneading disperger with a consistency of 15-35%. The specific operation transferred during the dispersion is 60 kWh/t. The fractionation is carried out in partial hydrocyclones with a consistency of 0.3-0.7%, and with a pressure sorter, which is equipped with a sieve. The openings in the sieve are slits, which have a slit-width of 0.1-0.15 mm. The fractionation of the products (A1) of the floatation is carried out in a washing device and/or a screw press. A bleaching is carried out before or during the dispersion. The rough fraction is treated in a bleach under supplying bleaching chemicals (CH1). The products of the second floatation are treated in the bleach where the bleaching chemicals (CH3) are to be supplied. The bleaching chemicals (CH3) guide to a reduced bleach.

Description

The The invention relates to a method for removing contaminants from an aqueous pulp suspension according to the Preamble of claim 1.

method The said type are used to make a paper fiber suspension at least a portion of the unwanted suspended therein Solid particles, so-called impurities, excrete. As is known, in a flotation with excreted substances formed foam or scum formed. A typical one Use case of such a method is the treatment from an aqueous recovered from printed paper Fiber suspension in which the ink particles are already made of fibers are detached so that they can float out. Of the flotation process described here exploits the differences between Paper pulp and unwanted particulate matter in the type that the pulp due to its rather hydrophilic character remains in the fiber suspension while the mentioned Particles are hydrophobic and therefore together with the air bubbles get into the foam. In addition to the ink particles, there are also a variety of other substances that are hydrophobic and therefore can be separated from the pulp by flotation. Such substances are in particular glue, fine plastic particles and possibly also resins. Because of the flotation process mentioned here Fibers are separated from impurities (both are solids), This is called "flotation deinking." usually not just for the removal of ink particles (ink = ink), but also more generally for flotation used by impurities from pulp suspensions.

There are widespread processes with two successive flotation steps, between which a mechanical treatment is carried out. So is from the technical essay Herbert Britz "Flotationdeinking - basics and system integration", Wochenblatt for Papierfabrikation 10, 1993, pages 394-401 It is known to use first a "flotation I", then a high consistency dispersion for its accept and then a "flotation II" to remove the inks released during dispersion of the fiber.

Such Procedures are very effective, but relatively complex since each substep is a complete selective flotation for the entire paper pulp.

Of the Invention is based on the object, a treatment process to create, with the most effective elimination the contaminant particle is achievable, so that the treated Fiber suspension also for higher quality papers, Sanitary paper (tissue), cover layers for cartonboard or white covered testliner is suitable.

These The object is achieved by the characterizing features of claim 1 solved in full.

The method according to the invention makes use of the possibilities which result from the fact that initially only a part of Pulp suspension is dispersed, namely, the reason its nature makes higher demands on the flotation. After dispersion, it is less expensive by flotation to clean, so that he is similar in this regard behaves like the other part of the pulp suspension. Especially advantageous is the subsequent fractionation or washing, because then again a selective dispersion can take place.

typically, the method is applied to waste paper suspensions. Such Starting material contains a mixture of different Fibers and impurities. This mixture is separated by fractionation only a small proportion of colorants and / or fillers in the coarse fraction transferred while the Fine fraction larger amounts of floatable impurities contains and with fiber fines and possibly short fibers enriched. In a fine fraction thus formed are the flotation conditions significantly cheaper than in the pulp suspension before fractionation. This is true even if the dispersed Coarse fraction was mixed. The flotation of the dispersed coarse fraction together with the fine fraction can also z. B. with higher Consistency can be brought to a good result. When used the process of the invention can readily be floated at about 1.5% or more while z. B. the usual Vollstromflotation at a consistency of about 1.0-1.3% becomes. Other possibilities of influence on the flotation offer z. B. variations in chemical dosage, amount of air bubbles or Plant size.

The The invention and its advantages are explained with reference to Drawings. Showing:

1 : An exemplary scheme of the method according to the invention;

2 Schematic: A plant according to the invention for the in 1 shown method.

1 shows a simple scheme in which waste paper in a pulper 13 a pulp suspension is formed. This is followed by a mechanical cleaning system 14 for the excretion of Verun cleaners, which are usually screening machines and / or centrifugal, z. As hydrocyclones, but still no flotation plant includes for deinking. The prepurified aqueous pulp suspension S thus produced becomes next to a first fractionation 2 fed. In one embodiment of the method, the fibers, which are significantly longer, possibly also stiffer than the other fibers, and large contaminant particles are guided into the coarse fraction G, while the short fibers, fines, fillers and fine contaminant particles get into the fine fraction F. This consideration covers only the solids; the liquid, which is predominantly water, flows off with both fractions. This may result in shifts in consistency, usually in such a way that the fine fraction F has a lower consistency than the coarse fraction G. Like the 1 shows, the fine fraction F is in a flotation 1 guided and there in the known manner of impurities such. B. ink particles, cleaned. This flotation 1 can be tuned with respect to their operating parameters to a particularly enriched with short fibers and / or fines suspension. The processes in flotation 1 are known; a flotation foam R1 is formed, which contains a large part of the impurities, and a purified accept A1 with the predominant part of the fibers.

The coarse fraction G of the fractionation 2 is through a thickening 4 brought to a higher consistency, preferably between 15% and 25%, possibly also heated, then undergoes a dispersion 5 and then a dilution 6 with water W, z. B. to about 1 to 1.5% consistency. Here, the main purpose of a dispersion 5 in such an application, the detachment of contaminants adhering to the fibers and the comminution of larger free contaminants, especially large ink particles. Possibly also other achievable with dispersers effects such. B. Resolution of the residual lip, be associated with it. Often an oxidizing bleach is useful at this point, as indicated by the addition of bleach chemicals CH1. After dilution 6 the substance also enters the flotation 1 ,

Already released to a large extent from floatable impurities accepts A1 flotation 1 will be in a further fractionation 3 out, which can be designed as Siebfraktionator or as a laundry. The one in the fractionation 3 Thickened material, ie the coarse fraction G3, becomes a further dispersion 8th fed, usually after further thickening 7 , Again, depending on the requirements and operating conditions, a warming of the substance is appropriate. In addition, CH2 can be bleached by the addition of oxidizing bleach chemicals, e.g. B. as an alternative to the first dispersion 5 made bleach. After this dispersion 8th is again in a dilution 9 with water W set a consistency, allowing for further selective flotation 10 is cheap. Their reject R10 carries off other contaminants. The fine fraction F3 of the fractionation 3 Contains fine impurities, mostly mineral fillers and possibly fiber fragments. It is now possible to remove the solid particles present in this fine fraction F3 from the system, for. B. via a Entstoffung 12 and then discard or use elsewhere. Depending on the requirement, however, it may also be desired to leave these particles in the material cycle by at least partially in the further flotation 10 be guided. In many cases, it will make sense to accept the A10 flotation 10 in a preferably reducing bleaching stage 11 to which the bleaching chemicals CH3 are added. It may also be beneficial to include the solids in the filtrate F3 at the flotation 10 past the bleaching stage 11 to lead (dashed line 26 ).

The Sequence of the bleaching stages: First oxidizing in a low-acid content Bleaching coarse fraction and later reducing in full flow, is often the cheapest method. In other cases can be bleached first reductively and then oxidatively.

The 2 shows somewhat more detailed representations of a device usable for the method, without here constructive mechanical embodiments could be removed. This is a pulp suspension in a pulper 13 formed, via hydrocyclone 15 as well as sorters 16 mechanically cleaned and then a first fractionation 2 fed. For the first fractionation 2 For example, a wet sifting machine of the type of pressure sorter equipped and operated according to the requirements of fractionation is used. So it should not serve for the separation of pollutants, get in the most possible all fibers in the run. In contrast to pollutant removal ("sorting"), the overflow also consists to a large extent of fibers during fractionation The pulp suspension S is pumped into the interior of the housing of such a pressure sorter and with the aid of a screen basket 17 fractionated. The parameters required for fractionation in the pressure sorter are known per se; the most important are the shape and size of the sieve openings, consistency of the suspension, overflow rate and type of sieve clearing. Typical sieve openings are round holes in the range between 0.2 and 0.5 mm or slots between 0.1 and 0.3 mm.

By choice of devices and operating conditions to realize the fractionation 2 can be the division of the pulp in coarse and fine fraction set. It may be of be be a special advantage, the fractionation 2 in such a way that as many fibers as possible, whether short or long, enter the coarse fraction G and the fine fraction F essentially contains the contaminants to be sorted out, inorganic fines (fillers) and organic fines (fiber fines). Such a special fractionation is performed in accordance with 3 used pressure sorter favored by relatively low consistency, with the screen openings rather relatively small values, ie z. B. about 0.2 mm hole or 0.1 mm slot to choose. The overflow rate would be relatively high, z. B. about 50%, with such values relate to the respective solids content of the suspension.

Of the Proportion of fibers is usually called the residue of the sieve R 100 determined according to Bauer-McNett (laboratory method according to TAPPT standard T 233). Fines fall in the same analysis as the run of the 100 mesh screens.

The consistency of the coarse fraction G from the fractionation 2 is through thickening 4 increased to a value between 15 and 25%. This is exemplified by a screw press 19 indicated; as you know, there are other thickening apparatus that may work in several stages. The filtrate 14 from this thickening 4 can z. B. to form the pulp suspension S in the pulper 13 be used. The thickened material then passes through a not shown transport screw system in a Scheibendisperger 18 in which, as is known, toothed dispersing tools are moved at a short distance relative to one another, which cause high-shear dispersion by dispersing the high-consistency substance. Alternatively, a kneader instead of Scheibendispergers 18 be used. Normally, it is expedient to heat the intended for dispersing high-consistency substance, for. B. to a temperature between 80 ° and 95 ° C. For this purpose, as indicated here, a direct feed of steam D in the Scheibendisperger 18 respectively. The specific work involved in the dispersion 5 is transferred to the pulp is usually set to a value between 30 and 120 kWh / t, preferably about 60 kWh / t.

The fine fraction F of the fractionation 2 is mixed with the dispersed and diluted coarse fraction G and into the flotation plant 20 directed. This can consist of several stages. In it, with the help of air L, the floatable impurities R1 are removed.

The new method can be advantageously designed so that after fractionation 3 made selective flotation 1 the first one is in preparation. In addition to the possible savings this has the advantage that the resolution 13 gentler, z. B. can be made with less chemicals. The fractionation 3 leads the fibers associated with printing inks in the coarse fraction G, which is dispersed, whereby a targeted separation occurs. The following wash or flotation removes the detached inks.

The accept A1 from the flotation plant 20 is fractionated. This fractionation 3 takes place here in a washing device 30 , The filtrate of the washing device 30 is then the fine fraction F3. As is known, in a wash a certain proportion of very fine solids from the supplied suspension is removed, while possibly retained all fibers and forwarded as accepts. Unlike a sorter, the unwanted substances remain in the fine fraction in a wash, which is why it could also be called a reject. Such washing devices for fibrous materials are known. They serve not only to separate the water from the solid (filter), but also to fractionate the solid itself. A particularly suitable technical embodiment and the preferred parameters are, for. B. in the patent DE 30 05 681 described. In such a washing device, the suspension to be washed becomes between an impermeable cylinder 31 and a permeable circulating screen belt 32 injected with low consistency turbulent. The between sieve belt 32 and cylinders 31 dewatered and washed pulp is then thickened as Acid A3 7 and further dispersion 8th guided. There are also known similar devices with two rotating screen belts known. An example shows the EP 0 341 913 ,

Also in 2 before dispersion 4 arranged screw press 19 may be the same or in similar form as a device for the fractionation carried out at this point 3 serve. Since the thickened material is constantly moved on the screen of the screw press, a fractionation is also possible here with a low consistency, in which a part of the fines and short fibers reaches the fine fraction F to a greater extent.

generally known but you can also fractionate fibers in hydrocyclones, where a consistency between 0.3% and 0.7% particularly favorable is.

The dispersion 8th coarse fraction G3 from fractionation 3 can be carried out similarly as it is based on the first dispersion 5 already described. There is thus a further thickening 7 and then a dispersion 8th , possibly with heating. The dispersed pulp is in a dilution 9 mixed with water W and then in another flotation 10 treated, what here the flotation plant 21 is used, which in principle similar to the flotation plant 20 for the flotation 1 can be constructed. Maybe the flotation plant 21 for further flotation 10 but designed to be significantly smaller, which is an advantage both from the operation, as well as the investment. The accept A10 of the flotation plant 21 is advantageously by a bleach 11 brought to a higher degree of whiteness. This is a reducing style of bleaching 11 at this point of advantage, especially at higher ash content. The reject R10, ie the flotation foam of the flotation plant 21 becomes a rejection editor 25 fed and z. B. be disposed of.

As a rule, it is no longer necessary to provide a further (ie third) selective flotation. Rather, the invention offers the possibility to save further flotations, since mostly by the two flotations 1 and 10 an already fully satisfactory flotation result can be achieved. Even a previously required total floatation prior to fractionation can be omitted, resulting in a considerable saving.

The fine fraction F3 of the fractionation 3 , in this case the filtrate from the washing device 30 , is either to the disperger 8th supplied fibrous material, for. B. for dilution 9 or it becomes a dedusting 12 in a plant for relaxation flotation 22 carried out. As is known, practically all solids in a flotation foam are collected and removed by very fine air bubbles in a flotation flotation DAF. What remains is a fairly usable return water, which is used for dilution or rinsing purposes. With the help of a regulator 23 , the z. B. supplied with signals indicating the pulp quality, a division of the fine fraction F3 can be done. In this way, a compromise between desired pulp quality and yield of the process can be found. It is understood that this trade off may vary depending on the raw materials, process conditions and requirements for the paper produced.

It is known in stock preparation for pulps and it is customary that the process steps which are carried out for the separation of undesired constituents of the pulp suspension are designed in one or more stages. By "multistage" it is meant that the first stage rejects serve as a feed to the second stage, the reject of which is then either discarded or passed into at least one further stage (eg third stage) Cleanliness of the first stage is clean and that this cleanliness does not have to be paid for by excessive fiber losses, in other words the further stages serve to recover usable fibers, thus increasing the yield of the entire process. B. cleaning system 14 , Hydrocyclone 15 , Sorter 16 , so they can be multi-level. The last reject (waste symbol) then comes from the last stage.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 3005681 [0022]
• EP 0341913 [0022]

Cited non-patent literature

• - Herbert Britz "Flotation Deinking - Fundamentals and System Integration", Wochenblatt für Papierfabrikation 10, 1993, pages 394-401 [0003]

Claims (24)

Process for the removal of impurities from an aqueous pulp suspension (S), in particular pulp suspension (S) formed from printed waste paper, wherein fractionation ( 2 ) from the pulp suspension (S) a fine fraction (F) and a coarse fraction (G) is formed, wherein the fine fraction (F) in a flotation ( 1 ), which is the first flotation in the treatment course of the process and wherein the coarse fraction (G) is dispersed, floated and then subjected to further fractionation ( 3 ), in which a fine fraction (F3) and a coarse fraction (G3) are formed, characterized in that the coarse fraction (G3) of the further fractionation ( 3 ) is redispersed. Process according to claim 1, characterized in that the further fractionation ( 3 ) is a wash. A method according to claim 1 or 2, characterized in that the fine fraction (F, F3) in the fractionation ( 2 . 3 ) with short fibers and the coarse fraction (G, G3) is enriched with long fibers. Process according to Claim 1 or 2, characterized in that the fraction (F, F3) in the fractionation ( 2 ) is enriched with fines and the coarse fraction (G, G3) with long and short fibers. Method according to one of the preceding claims, characterized in that the coarse fraction (G3) of the second fractionation ( 3 ) after further dispersion ( 8th ) in another flotation ( 10 ) is treated. A method according to claim 5, characterized in that at least a part of the fine fraction (F3) of the further fractionation ( 3 ) into the further flotation ( 10 ) to be led. Method according to claim 5, characterized in that that the solids of at least part of the fine fraction (F3) be removed. Method according to claims 6 and 7, characterized that the division of the fine fraction (F3) to regulate the quality of the pulp is adjusted. Method according to claims 6 and 7, characterized that the division of the fine fraction (F3) to regulate the yield of the procedure is set. Method according to one of the preceding claims, characterized in that the selective flotation (F) processing the fine fraction (F) and at least part of the dispersed coarse fraction (G) ( 1 ) is the first selective flotation in the processing course of the process. Method according to one of the preceding claims, characterized in that the selective flotation ( 1 . 10 ) is carried out at a consistency between 0.8 and 2.5%, preferably 1.0 to 2%. Method according to one of the preceding claims, characterized in that the dispersion ( 4 . 8th ) is carried out in a disk disperger or kneader at a consistency of between 15 and 35%. A method according to claim 12, characterized in that in the dispersion ( 4 . 8th ) transferred specific work between 30 and 120 kWh / t, preferably about 60 kWh / t. Method according to one of the preceding claims, characterized in that the fractionation ( 2 . 3 ) is carried out at a consistency between 0.6 and 4%. Method according to one of the preceding claims, characterized in that the fractionation ( 2 . 3 ) is performed with a pressure sorter equipped with at least one sieve. Method according to claim 15, characterized in that that the openings in the sieve are slots that have a slot width between 0.08 and 0.3 mm, preferably 0.1 to 0.15 mm. Method according to one of claims 1 to 14, characterized in that the fractionation ( 3 ) in at least partially hydrocyclones at a consistency of between 0.1 and 2%, preferably 0.3-0.7%. Method according to one of the preceding claims, characterized in that the fractionation ( 2 ) of the pulp suspension (S) in a washing device ( 30 ) is carried out. Method according to one of the preceding claims, characterized in that the fractionation ( 3 ) of the accept (A1) of the flotation ( 1 ) in a washing device ( 30 ) is carried out. Method according to one of claims 1 to 18, characterized in that the fractionation ( 3 ) of the accept (A1) of the flotation ( 1 ) is carried out in a screw press. Method according to one of the preceding claims, characterized in that a bleach before or during the dispersion ( 5 . 7 ) is carried out. Method according to one of the preceding claims, characterized in that the coarse fraction (G) in a bleach treated with the addition of bleaching chemicals (CH1). Method according to one of the preceding claims, characterized in that the accept (A1) of the second flotation (A1) 10 ) in a bleach ( 11 ), to which bleaching chemicals (CH3) are added. Method according to claim 23, characterized that the bleach chemicals (CH3) cause a reducing bleach to lead.