GB2172525A

GB2172525A - A method for the processing of waste paper

Info

Publication number: GB2172525A
Application number: GB8604773A
Authority: GB
Inventors: Helmut Konecsny; Siegbert Fischer
Original assignee: JM Voith GmbH
Current assignee: JM Voith GmbH
Priority date: 1985-03-21
Filing date: 1986-02-26
Publication date: 1986-09-24
Also published as: ATA19386A; GB8604773D0; AT389530B; CH670120A5; FR2579237A1; DE3510214A1; GB2172525B

Abstract

In a method for processing waste paper, the waste paper is firstly pulped in a breaker and then subject to preliminary cleaning. Prior to flotation and subsequent washing and bleaching, the fibrous suspension is treated in a dispersion plant, comprising an inlet and preliminary heating coil followed by a dispersion device, at a temperature of at least 50 DEG C. As a result, paper of the highest purity can be produced even with a high NCR content in the waste paper, e.g. for paper of tissue quality.

Description

SPECIFICATION Method for Processing Waste Paper The invention relates to a method for processing waste-paper of the kind in which after pulping in a breaker and preliminary cleaning the fibrous suspension is firstly separated by the flotation method, then washed and finally bleached.

Such a method has become known from German-AS 26 581.

In contrast with the disclosure of the abovenamed German-AS, the object of the invention is to provide a particularly pure fibrous suspension for paper of tissue quality or comparable quality in particular, both in the case of woody and also a wood-free waste paper content.

The object is solved in accordance with the invention by the features of the characterising part of Patent Claim 1. It has been shown that, contrary to previous opinion, even with a high no carbon required (NCR) content in waste paper, no harmful effects occur as a result of the dispersion, but that, on the contrary, a particularly good effect is achieved with this method, so that no patches of colour occur in the finished paper. It has been shown that in this way particularly effective bleaching can be carried out either in one stage or in two stages. It is advantageous to carry out the heating of the fibrous suspension infrontofthe dispersion device in the condensing or heating coil which is normally connected infront of the dispersion delvice.

The invention is explained below by means of an exemplified embodiment, the procedure of which is summarized in principle in the attached figure.

The waste paper is pulped in a breaker 1 with the addition of fresh water from a tank 3 and then the fibrous suspension is conveyed by means of pump 4 into an intermediate vat 5. From this the suspension is pumped by pump 4 into a hydro-cyclone plant 6 for the purpose of separating the heavy material, after which in this preliminary sorting is carried out in a secondary breaker 7, from which a half-stuff is separated by a strainer 7a into a small half-stuff chamber 7b. After that a vertical screen 8 having small perforations and a hydro-cyclone plant 9, consisting generally of several successively arranged cleaners switched in parallel, are provided as cleaning stages so that thorough cleaning is carried out.

Then follows the dispersion plant which includes a heating helical screw 11 and a dispersion device 12 (e.g. a single, or double shaft refiner or disintegrator). Any contamination is removed at this early stage by preliminary sorting, and dispersion at the appropriate temperature causes the dissolution or release of printing inks, e.g. especially of varnish colours, and a reduction in the microcapsules of the NCR content. The heating process in the heating screw is very short, so that the quality of the fibrous material is not impaired. The temperatures in the dispersion process may rise to 135 , but are preferably in the approximate range of 50-1100.

For dispersion the stuff is brought to a solids content of at least 20% in a concentrator 10. As the fibration plant 15 now follows, dilution by diluting water is carried out, which is supplied through line 35, and furthermore the chemicals are added for flotation. Amongst these chemicals the most important are frothers and accumulators. According to the method of the invention,theflotation composition could be as follows: 2% NaOH, 1% Serfax, 3% water glass (37 B'e), 1% H202 (Peroxide, 100% calculated), 0.3% DTPA (customary complex former, e.g. Darotin D 5 from the company Degussa).

However, of these chemicals only the soap is added just in front of the flotation plant. All the other chemicals, in particular sodium hydroxide, are supplied to the process in front of the dispersion plant.

Here the flotation plant can be constructed somewhat smaller than usual, as there is still a washing operation to be performed in washing plant 16, 18, 20, and in fact the half-stuff arrives at a storage tank 13 after the flotation plant. It is known that the scum removed from the flotation plant can be received in a storage tank 27 so as to clean it further. The washing plant consists, for example, of two or three inclined strainer washers connected one being the other (Sidehill system) and having inclined strainers 18. After the washing plant the fibrous suspension arrives at the collection vat 21 with a consistency of 4 to 5%. A combination of other machines, e.g: inclined strainer washers and water extractors, is also possible.

Subsequently a one-stage or two-stage bleaching operation takes place, either with sodium hydrosulfite (Na2S2O4), or this bleaching operation is performed as the second stage with a preliminary hydrogen peroxide bleaching operating, which could be advantageously carried out before dispersion as rapid bleaching, in particular with woody material. Otherwise the single-stage bleaching operation is, however, sufficient to obtain a whiteness of 80 to 85%, measured on the Elrepho device,filterF8(BaSO4 = 100%).

Pulping in the breaker 1 should be performed at low temperatures of below 35 to 40"C as far as possible, so that it is easier to sort adhesive constituents. Furthermore ail impurities which can be removed with mechanical sorting machines should be eliminated before dispersion in the sorting plant 11, 12, so as to keep the load on the flotation, washing and bleaching operations as small as possible. Furthermore dispersion also gives the further advantage that impurities which can not be sorted and which are also partly adhesive are dispersed by perfecting so that they cause less problems on the paper machine, e.g. tissue machine.

A pulp density of 4 to 5% and a temperature of 60"C is recommended for bleaching with sodium hydrosulfite. Bleach should be added in the magnitude of 1% (commercial goods), and it is best to carry out bleaching in the presence of 0.3% DTPA with a pH-value of less than 9.

In the Figure it is also shown that the washing water produced in the washing plant can be collected in the tank 24 by means of lines 22 and 23 for processing in a clarification plant 28. The clarified water can be used again as washing water in washing stages 18 or 20 respectively via lines 37 and 39. The scum from the clarification plant and flotation can also be ridded of a large part of the water contained therein in corresponding centrifuges 31 and 26 respectively, and the water can be fed back via lines 25 or 34 respectively to be used again in the process.

As office waste, for example, is mainly used for tissue qualities, a considerable proportion of NCR paper is always to be expected in the processed waste paper; its content can fluctuate between 0 and 100% and it is generally between 20 and 50%.

With the method according to the invention, however, the colour effect of these paper qualities can be reliably avoided in the tissue quality.

Moreover, in this case it should also be noted that these NCR papers very often have other aldditional legends in varnish colours, but these colours are either eliminated or dispersed reliably with the method according to the invention by dispersion and a combination of flotation and washing operations. In this way the high whiteness values of 80 to 85, and even 88, can be achieved. It should be noted that frequently paper made from processed waste paper has a good whiteness, but that its purity often leaves a lot to be desired, as it is difficult to achieve this purity per se with conventional measuring methods. Many sorts of waste paper also require a movement into the grey blue range through the black color spectrum, but with the invention an absolutely greater lightness and whiteness is achieved. Of course this also relates to paper dyed when pulp.

Furthermore it was also established that the often conventional dispersion of the finished stuff, i.e. at the end of the processing operating, did not produce a good effect, but is rather associated with a significant loss of whiteness.

Claims

1. A method for the processing of waste paper, in which after pulping in a breaker and preliminary cleaning the fibrous suspension is firstly separated by the flotation method, then washed and finally bleached, characterised in that when using the method on waste paper containing a considerable amount of NCR waste paper constituents for the purpose of achieving high whiteness and purity for high-quality paper, e.g. tissue, prior to flotation the fibrous suspension is treated by temperatures of at least 50 in a dispersion plant comprising a dispersion device (12) and an inlet and pre-heating helical screwforthe dispersion device, in which the temperature is increased to at least 50"C.

2. A method according to Claim 1, characterised in that dispersion is carried out at more than 85do.

3. A method according to Claim 1 or 2, characterised in that thorough cleaning is carried out in sorting devices (8, 9) upstream of the dispersion stage (15).

4. A method according to any one of Claims 1 to 3, characterised in that the method is used with waste paper having a NCR content of 10 to 100%.

5. A method according to any one of Claims 1 to 4, characterised in that the bleach is a single-stage dithionite (sodium hydrosulfite) bleach.

6. A method according to any one of Claims 1 to 5, characterised in that no chemicals or substantially no chemicals are used in the breaker and the maximum temperature is 40"C.

7. A method according to any one of Claims 1 to 6, characterised in that the pulping and flotation chemicals are added right up until the soap in front ofthedispersion plant (11,12).

8. A method according to any one of Claims 1 to 7, characterised in that the dispersion device (12) used in the method is a single, or double shaft disc perfecter.

9. A methods for the processing of waste paper, especially waste paper with a high NCR content substantially as hereinbefore described with reference to the accompanying drawing.

10. Apparatus specifically adapted to carry out a method of processing waste paper as claimed in any one of Claims 1 to 9, having a dispersion plant comprising an inlet and preheating coil and a dispersion device (12).