AU2004203404A1

AU2004203404A1 - Process for Treating Disruptive Vessels Containing Fresh Cellulose

Info

Publication number: AU2004203404A1
Application number: AU2004203404A
Authority: AU
Inventors: Harald Selder
Original assignee: Voith Paper Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2003-08-18
Filing date: 2004-07-27
Publication date: 2005-03-10
Also published as: BRPI0403189A; DE10337821B3; EP1508638A1

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Address for Service: Invention Title: Voith Paper Patent GmbH CULLEN CO.

Level 26 239 George Street Brisbane QId 4000 Process for Treating Disruptive Vessels Containing Fresh Cellulose The following statement is a full description of the invention, including the best method of performing it, known to us: TECHNICAL FIELD The present invention relates to processing of cellulose. In particular, the invention relates to a process for treating fresh cellulose suspension containing disruptive vessels by which process the harmfulness of the vessels is adequately eliminated.

BACKGROUND ART It is known that fresh cellulose, for whose production fast-growing foliage, in particular tropical foliage is used, contains so-called vessels, which have relatively large dimensions as a result of climatic conditions. Their quantitative portion of cellulose is mostly 3 to These vessels are not removed during production of cellulose and become disruptive in paper manufactured from such cellulose, since they are responsible for certain disadvantages. Thus it can e.g. eventuate that the vessels break out of the paper texture, whereby the surface deteriorates and the paper properties are impaired.

Unlike the cellulose fibres they have a hydrophobic character.

A process is already known from DE 198 16 621 Al for solving this problem, but it has its limits if the cellulose fibres are undesirably altered by the milling used.

The object of the invention is therefore to provide a process, enabling the disadvantages, resulting from the vessels content, to be reduced or completely eliminated and at the same time to obtain the best possible desired properties, such as e.g. specific volume.

SUMMARY OF THE INVENTION in a broad format, the invention provides a process for treating fresh cellulose suspension containing disruptive vessels, in particular made of foliage, by which the harmfulness of the vessels is adequately eliminated, characterised in that the mixture of cellulose fibres and vessels is dispersed at a high consistency, preferably between 15 and An outcome of the inventive process is that the losses in quality, a threat from the abovementioned vessels for the paper later produced from the cellulose, no longer occur.

The majority of the vessels can be removed, and those vessels possibly not removed are anchored (felted) in the fibre compound such that they remain there, even when the paper is stressed.

-3- The process is usually utilised in stock preparation in a paper factory. But such a process can already be carried out in the cellulose factory after repulping.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be explained with reference to diagrams, in which: Figure 1 shows a simplified example of the process; Figure 2 shows a diagram; Figure 3 shows a simplified process variant.

BEST MODE AND OTHER MODES OF CARRYING OUT THE INVENTION The diagram of Figure 1 shows an important example for executing the process. The cellulose 1 is brought to a consistency of between 15 and 35% in suspended form or after dissolving not shown in water and optional cleaning in a concentrator 2. Ensuing dispersing takes place here in a disc disperser 3 known from waste paper preparation. In other cases a kneading disperser can be utilised. The fittings of disc dispersers have a very large number of slots and are moved past one another relatively quickly. An example is shown in DE 30 47 013 Al. Kneading dispersers (see e.g. DE 42 37 433 Al) o the other hand have a coarser structure and work at slower relative speeds.

After the dispersed material 4 is diluted in the tub 16 in the embodiment shown here the suspension is pumped through a hydrocyclone plant 6 with a pulp pump 5. The hydrocyclone plant 6 generally consists of a large number of highly effective hydrocyclones, so-called cleaners, which work with centrifugal fields reaching at least 200 times gravitational acceleration. These too are known from waste paper preparation.

Vessels are separated out using the reject 7 of these cleaners, while the accept 8 constitutes a raw material for perfect paper quality. Apart from the advantage of the accept 8 of containing no harmful vessels, the fibres are also in a good state, in particular with respect to draining properties on the paper machine and specific volume of the paper produced. The fibres contained in the reject 7 can be recovered by other cleaning steps (not shown) possibly in connection with mechanical processing.

In the diagram in Figure 2 the particle size 9 of the vessels is outlined at the bottom in the range of 0.1 to 1 mm, increasing to the right. The ordinate shows the flat frequency 10 of -4the vessels found in the sample leaf, e.g. measured in 1/mm 2 The diagram has four curves, showing the interrelationship, depending on which treatment the used cellulose has undergone. The uppermost of these curves, curve 11, constitutes the frequency distribution of the vessels in the cellulose 1, before the latter was subjected to the inventive process. At the same time in the starting state the flat frequency 10 at a small particle size 9 is relatively high and tapers off to increasing particle sizes. The dispersed material 4 already has a clearly better quality, shown schematically in the curve 13. After completion of the process in the form illustrated in Figure 1 the accept 8 of the hydrocyclones has the distribution entered in curve 14, i.e. there are hardly any vessels still present. In a comparative test the curve 12 has been determined, which lies between the curves 11 and 13 and which describes the state after hydrocyclone bypassing the disc disperser 3. It can also be stated that dispersing already solves the problem posed and that an excellent fibrous material can be produced in particular through the combination of both procedural steps, which is practically free of disruptive vessels. Even when there is still a residual of vessels present in the accept 8, these are very strongly felted with the cellulose fibres, as is clearly established by means of raster-electronic recordings of leaves formed from this suspension, so that no effect impairing the quality can come from the latter any longer.

The diagram according to Figure 2 shows the correlations qualitatively only. Depending on the type of cellulose and choice of parameter deviations from this path are feasible, whereby the basic improvement is clearly confirmed by the inventive process.

A possibility of solving the problem of the vessels using another configuration of the inventive process is illustrated in Figure 3. Accordingly, the cellulose fibres are cleaned of vessels in the hydrocyclone plant 6, though already prior to dispersing. Then the reject 7" of the hydrocyclone plant 6 is strongly enriched with vessels, so that the subsequent dispersion treatment can focus on comminuting and felting these vessels. Because of the considerably smaller quantity energy consumption and equipment expense are limited, making this variant particularly economical. Even fibre losses and fibre damage can be prevented more easily. After dispersing and optional dilution the fibrous material can be again added to the accept 8' of the hydrocyclone plant 6, resulting in a suspension which is free of disruptive vessels. The remaining vessels contained in the accept 8" of the hydrocyclone plant 6 are so small that they barely disturb this partial flow without dispersing.

The term "comprise" and variants of the term such as "comprises" or "comprising" are used herein to denote the inclusion of a stated integer or stated integers but not to exclude any other integer or any other integers, unless in the context or usage an exclusive interpretation of the term is required.

Any reference to publications cited in this specification is not an admission that the disclosures constitute common general knowledge in Australia.

Claims

1. A process for treating fresh cellulose suspension containing disruptive vessels, in particular made of foliage; by which the harmfulness of the vessels is adequately eliminated, characterised in that the mixture of cellulose fibres and vessels is dispersed at a high consistency, preferably between 15 and

2. The process as claimed in Claim 1, characterised in that after dispersing the mixture is fractionated at a low consistency, preferably below 3% in hydrocyclones and in that at least the majority of the vessels are separated out in hydrocyclones at a consistency below 3%.

3. The process as claimed in Claim 1, characterised in that the majority of the vessels are separated out as reject by hydrocyclones from the mixture at a consistency below and in that the reject is then dispersed at a consistency of between and

4. The process as claimed in any one of Claims 1 to 3, characterised in that the dispersing is carried out in a disc disperser at a consistency of 25 to 35% and that specific work of more than 70 kWh/t is transmitted.

The process as claimed in any one of Claims 1 to 3, characterised in that dispersing is carried out in a kneading disperser at a consistency of 25 to 35% and in that specific work of more than 90 kWh/t is transmitted.

6. The process as claimed in any one of Claims 1 to 5, characterised in that dispersing is carried out at a temperature below 70 C.

7. The process as claimed in any one of Claims 1 to characterised in that a consistency of less than preferably below is set at the inlet in the hydrocyclone.

8. The process as claimed in any one of Claims 1 to 7, characterised in that a reject flow is continuously drawn off on the hydrocyclone, whereof the magnitude corresponds to 10 30 vol% of the supply flow to the hydrocyclone. -7-

9. A process for treating fresh cellulose suspension containing disruptive vessels, which process is substantially as hereinbefore described with reference to the section entitled "Best Mode and Other Modes of Carrying Out the Invention". A process for treating fresh cellulose suspension containing disruptive vessels, which process is substantially as hereinbefore described with reference to Figure 1 or Figure 2. Voith Paper Patent GmbH By the patent attorneys for the applicant CULLEN CO. Date: 27 July 2004