FI95290C - Method and apparatus for decolourizing recycled paper - Google Patents

Description

95290

A method and apparatus for removing ink from a collection head

The present invention relates to a method and apparatus 5 for removing ink from recovered paper. In particular, the invention is directed to streamlining the flotation process used to remove ink.

10 recovered paper dispersed by water, chemicals and mechanical forces, so-called recovered paper pulp, typically containing fibers and fiber parts of different sizes, paper fillers and additives, and inks. The ink is removed from the collection paper stock in an operation called a deinking process using washing and / or flotation methods. In the washing processes 15, the ink particles are washed from the recovered paper stock with water.

Washing processes most effectively remove ink particles with a diameter of less than 10 μπι: η from the recovered paper stock, with some of the larger particles retaining into the fibrous networks formed by the fibers, resulting in a poorer cleaning result. Another problem with washing processes is the high water consumption associated with them and the fact that a large amount of valuable fibrous material is washed from the recovered paper stock with the washing water. The fiber yield of washing processes is therefore typically at the level of 70-75%.

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In flotation processes, the ink particles contained in the recovered paper stock are removed using air bubbles that bind to the ink particles and bind to the ink particles. The ink is then enriched in the foam formed on the surface of the recovered paper stock 30, which is removed. Flotation is typically performed in a so-called in flotation cells, which are ·· to improve the flotation result, 4 to 12 pieces are usually connected together. The advantage of flotation processes over washing processes is lower water consumption and higher fiber yield, which is typically at the level of 90-95%.

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In order for the ink particles to be enriched in the foam formed on the surface of the stock during flotation, the ink particles and the air bubbles must first adhere to each other, provided that the impact velocity of the ink particle 5 and the kinetic energy relative to the air bubble are sufficiently high.

Thereafter, the air bubble and the ink particle attached to it must rise indistinguishably on the surface of the stock. However, even at very low concentrations, the fibers contained in the recovered paper stock interfere with the flotation process by forming fibrous networks in the stock which dampen the movement of ink particles and air bubbles, whereby the adhesion of the ink particles to the air bubbles is not effective. The networks formed by the fibers also slow down the transport of the air bubbles and ink particles 15 attached to each other on the surface of the pulp, thereby increasing the probability of separation of the air bubble and the ink particle attached to it. Flotation of recovered paper stock is the most effective way to remove ink particles with a diameter of 10 to 50 μιη. Due to the turbulence-damping effect of fibrous networks, the kinetic energy of very small ink particles is generally insufficient to adhere to air bubbles. Ink particles larger than 50 μιη in diameter are easily detached from air bubbles, especially when there is strong turbulence in the foamable pulp paper pulp.

Naturally, the longer the fibers and the higher their concentration, the greater the tendency of the fibers to form fibrous webs in the foamable recovered paper stock. In practice, the disadvantages caused to the flotation process of fiber networks have been solved by floting the recovered paper pulp at a very low solids content (0.7-1.5%), whereby the probability of fiber networks is lower, while strong turbulence increasing the impact velocity of air bubbles 55290. However, the low solids content has the disadvantage that large-scale flotation devices have to be used in flotation, in addition to which the water and energy consumption of the flotation process is high.

The object of the present invention is to eliminate the drawbacks associated with the prior art and to provide a completely new solution for removing ink from recovered paper from a stock. In particular, it is an object of the invention to treat recycled paper stock containing ink in such a way as to substantially avoid the formation of fibrous networks during the flotation step, whereby the cleaning efficiency and economy of the flotation processes are considerably improved.

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The invention is based on the idea that prior to flotation, the recovered paper stock is fractionated into a coarser fraction rich in long fibers and other coarse bodies and a finer fraction containing short fibers, paper fillers and additives and inks, at least substantially free of fiber networks. The method is characterized in that, compared to the dimensions of the fibers, typically small ink particles are fractionated mainly into a finer fraction. The process is also characterized in that the finer fraction purified in the flotation is combined with a pulp stock containing coarser material, after which the sorting and flotation of the pulp stock is repeated as described above to improve the cleaning efficiency.

According to a preferred embodiment of the invention, the finer fraction separated from the recovered paper pulp by the fractionator is passed to a coarser fraction after flotation so that part of the fraction is passed through a pipeline to the feeder coarser fraction separated in the fractionation device.

With a solution according to a preferred embodiment of the method described above, e.g. the following advantages: - the flotation result is improved because the finer fraction is floted substantially free of the formation of fiber networks.

- the yield of long fibers is improved because the long fibers are separated from the fraction to be foamed.

_ the finer fraction can be foamed at a higher solids content than the unfractionated stock, typically at a solids content of 1.5 to 2.5%, in which case smaller flotation devices are sufficient.

15 - water and energy consumption is reduced due to the higher solids content of the flotation.

In the following, the method and apparatus according to the present invention will be explained in more detail with reference to the accompanying Figure 1, which schematically shows a process for cleaning a recycled paper stock according to a preferred embodiment of the invention.

Characteristic features of the method and apparatus according to the invention are set out in the appended claims.

Figure 1 shows a process for cleaning a recovered paper stock according to a preferred embodiment of the invention, in which the treatment of the stock from the defibering and pre-sorting steps of the deinking process is exemplified.

The apparatus comprises a pipeline 1 for feeding uncleaned collection pulp-35, four 11 95290 fractionators 2 for forming a finer and coarser fraction, four flotation cells 3 into which a finer fraction containing substantially more ink is fed via four pipelines 4, and without the detrimental effect of fiber-5 networks. Channels 9 are provided in the flotation cells to remove the ink containing ink. The invention typically combines a finer fraction purified in flotation with a pulp containing coarser material, in the exemplary case 10 of Figure 1 via eight pipelines 6, 7 to pipelines 1, 5, 8, of which pipeline 1 is a feed line for untreated recovered paper pulp and . Through the pipeline 8, the waste paper-free recovered paper stock is transported to the next steps of the cleaning process. Since the lower the solids content of the recovered paper stock fed to the fractionator, the separation efficiency of the ink 20 can be adjusted feed relative to the feed of the pipelines 7, the separation of the ink into the finer fraction 25 can be enhanced, as a result of which the cleaning result is improved while the cleaning capacity of the equipment is reduced. The optimal feed ratio via pipelines 6 and 7 is, of course, process-specific.

The fractionation device 2 can be a pressure screen, a non-pressurized screen, e.g. an arc screen, or a scrubber, e.g. a filter belt press. The flotation device 3 can be a non-pressurized flotation cell, a pressurized flotation cell, or also a flotation device of the vortex cleaner type which substantially utilizes the centrifugal force and the lifting of air bubbles.

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As can be seen from the above, a new way of dealing with the disadvantages of the known solutions has been developed to treat the recycled paper pulp so that the cleaning efficiency of the flotation process is improved and the size of the equipment required for flotation 5 is reduced. It should be noted, however, that although a preferred embodiment of the invention has been described above, it is not intended to limit the invention to this exemplary embodiment only, but the scope and scope of the invention are only defined in the appended claims. Thus, it is clear that e.g. the terms fractionation device, flotation device and feed line used in the above description include all devices capable of performing the functions described above. The invention also does not limit the number of fractionation devices, flotation cells or supply lines connected to each other as described above.

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Claims (10)

1. Process for removing ink from recycled paper stock in which process only a finer fraction containing substantially more ink is flotated after fractionation and further after being decolorized by flotation, is combined with a recycled paper stock containing coarser pulp, characterized by of the following steps a and b: a. The recovered paper stock is fractionated in a coarser and finer mass of which only the finer fraction is flotated, and b. the fluted finer fraction is combined with the recovered paper stock containing coarser pulp Process according to claim 1, characterized in that steps a and b are repeated one after the other so that the finer fraction colored in the flotation is partially or completely joined to the recycled paper stock containing coarser pulp. This occurs before the fractionation apparatus where the finer fraction in question is formed. Method according to Claim 1, characterized in that steps a and b are repeated by joining the finer fraction formed and decolorized in the flotation partially or completely with a fractionator in which the feed line of the fractionator is fed coarser mass from the previous fractionation apparatus. 4. Device for decolourizing recycled paper stock, which consists of fractionation apparatus (2), flotation apparatus (3) and lines (1,4,5,6,7,8) needed to transport recycled paper stock, finer fraction, coarser fraction, fluted finer fraction, fluted finer fraction and recycled paper stock joined together, and fluted finer fraction and coarser fraction joined together, and foam effluent channels (9), characterized by the factoring devices provided at flotation cell feeding lines (2) by which the coarser fraction is separated from the recovered paper stock before the finer fraction is fed into the flotation apparatus (3). 5. Device according to claim 4, characterized in that the flotated finer fraction through the feed line (6) is partially or completely associated with the recycled paper stock containing coarser pulp. 6. Device according to claim 4, characterized in that the flotated finer fraction through the feed line (7) is partially or completely joined to the recovered paper stock containing coarser pulp. 7. Device according to claim 4, characterized in that the flotated finer fraction through the feed lines (6) and (7) is partially or completely joined to the recycled paper stock containing coarser pulp. Device according to claim 4, characterized in that the device comprises one or more fractionation apparatus (2) and one or more flotation apparatus (3) and as many conveyances (1,4,5,6,7,8) as necessary. 9. Device according to claim 4, characterized in that the fractionation apparatus (2) is a pressurized screen or a non-pressurized screen such as a cup screen. 10. Device according to claim 4, characterized in that the flotation apparatus (3) is a pressure flotation cell or a non-pressurized flotation cell or any corresponding decolorization apparatus. »II