WO2007107179A1

WO2007107179A1 - Method for treating cellulose which contains disruptive vessel cells

Info

Publication number: WO2007107179A1
Application number: PCT/EP2006/012158
Authority: WO
Inventors: Harald Selder
Original assignee: Voith Patent Gmbh
Priority date: 2006-03-21
Filing date: 2006-12-16
Publication date: 2007-09-27
Also published as: DE102006012835B3

Abstract

The method treats a cellulose suspension (1) which has a disruptive proportion of vessel cells. The latter are treated in a loading process (2) in such a way that fillers which accumulate on the vessel cells are formed by a chemical reaction. Said fillers can be removed subsequently by centrifugal forces, for example in hydrocyclones (9).

Description

Process for the treatment of pulp containing disruptive vascular cells

The invention relates to a method according to the preamble of claim 1.

As is known, such pulps, for the production of which fast-growing hardwoods, in particular tropical hardwoods, are used, so-called vascular cells (English: vessels), which have relatively large dimensions as a result of the climatic conditions. Their proportion of pulp is usually 3 to 5%. These vascular cells are not removed in the pulp production and are disturbing in the paper produced from such a pulp, as they are responsible for certain disadvantages. So it can be e.g. happen that the vascular cells break out of the paper structure, whereby the surface deteriorates and the paper properties are impaired.

Although a method is known from DE 198 16 621 A1 to solve this problem, but it finds its limits when the pulp fibers are changed by the grinding used in an undesirable manner.

DE 103 37 821 describes a process by means of which the removal of vascular cells by hydrocyclones after prior dispersion is made possible.

The invention is based on the object to provide a further method, with which it is possible to reduce or eliminate the disadvantages resulting from the content of vascular cells. It should have an improved overall economy, at least for special treatment processes.

This object is achieved by the features mentioned in the characterizing part of claim 1 Connection with those of the preamble solved.

The process is usually used in stock preparation at a paper mill. However, it can also be carried out in the pulp mill after digestion.

The loading of the vascular cells and fibers with mineral filler is carried out, for example, by a chemical precipitation reaction, i. in particular by a so-called "Fiber Loading ™" process, as described inter alia in US-A-5 223 090. In such a "Fiber Loading ™" process, at least one additive, in particular, is added to the wetted fiber surfaces of the fiber material Filler, stored. The fibers can be loaded with calcium carbonate, for example. For this purpose, the moist, disintegrated fiber material calcium oxide and / or calcium hydroxide is preferably added in liquid form (milk of lime) so that at least a part of it associates with the water present in the fiber material. The fiber material treated in this way is then treated with carbon dioxide. This causes a chemical reaction in which the calcium carbonate precipitates and attaches to the wetted fibers and vascular cells. This attachment can be done outside and inside, as pulp fibers and vascular cells are open hollow body.

Possible advantages of the filler particles obtained by loading a fiber suspension include, but are not limited to, the following:

It is now possible, the required filler evenly over the

To distribute the fiber surface, whereby the best optical properties are achieved online in the stock preparation, wherein the achieved filler level may be below or above 40%.

Since filler particles are also embedded within the fiber lumen, the

Tendency of a calendering significantly reduced.

A new way of incorporation of pigments is provided to achieve the desired optical properties and printability in and on the paper sheet in papermaking.

Since the filler particles are incorporated in the fibers, they can be in the sieve or

Langsiebpartie a paper machine can not be washed out. As the filler particles are incorporated into the fibers in an on-line process, ie in the

Pulp preparation system can be crystallized, can provide economic benefits through savings of retention agents, fibers and sludge, reducing the

White water pollution as well as the saving of energy and raw material can be achieved.

The use of TiO ₂ can be reduced after a higher whiteness and better optical properties can be achieved.

Vessel cells have the task of securing the transport of water in hardwood logs. As a rule, these vascular cells are lined with a lignin layer in the part through which water flows. This results in a strong hydrophobic character. Through the digestion process, this lignin layer is dissolved out leaving behind a porous and hydrophilic fiber material. Vessel cells have the property to be loaded particularly effectively due to this porosity. That is, they deposit and take up the precipitated fillers more than the pulp fibers. This increases their density and they can be effectively separated from the pulp fibers by centrifugal forces.

The combination according to the invention of the loading and hydrocycloning process steps ensures that the loss of quality threatening by the vascular cells mentioned above no longer occurs for the paper produced later from the pulp, since the vast majority of the vascular cells can be removed. In addition, the loading brings a significant quality improvement.

The invention will be elucidated with reference to a drawing, which schematically illustrates the most important steps of the method in a typical example.

Accordingly, a pulp suspension 1, which is mixed with interfering vascular cells, fed to a loading process 2. This is known per se. For example, calcium hydroxide 3 (lime milk) and gaseous carbon dioxide 4 are successively added and reacted. Measures for setting optimum reaction conditions are not shown here, since it is well known, for example from DE 102 04 254-A1, 100 33 979-A1 or EP 1 409 789. After dilution with water 6 (possibly also with filtrate 5 from the loading process 2) the loaded suspension 7 is brought by a pump 8 to an elevated pressure and pumped into a system with parallel connected hydrocyclones 9. Such hydrocyclones, also called cleaners, exhibit a considerable release effect at a consistency (dry content) of less than 3%. The loaded vascular cells can therefore be removed as heavy dirt in the reject flow 11. Particularly effective are continuously operated hydrocyclones with a relatively large reject flow 11, for example 5 to 20% by volume of the feed stream to the hydrocyclone. In order to avoid fiber losses through the reject flow 11, a secondary stage (not shown here) is usually operated for this. The Gustoffstrom 10 of the hydrocyclones 9 is sufficiently free of interfering vascular cells.

Bezuqszeichenhste

1. Pulp suspension

2nd loading process

3. calcium hydroxide

4. carbon dioxide

5. filtrate

6. Water

7. loaded suspension

8. pump

9. Hydrocyclone

10. Acceptance stream

11. Reject current

Claims

claims:

1. A process for the treatment of a pulp suspension containing interfering vascular cells (1), with the aim of sufficiently removing vascular cells, characterized in that fillers are attached to the vascular cells in a loading process (2) by chemical reaction and that thereafter the loaded vascular cells are separated by centrifugal forces at a consistency preferably below 3% as heavy materials.

2. The method according to claim 1, characterized in that in the loading process (2) a chemical reaction of calcium hydroxide or calcium oxide is carried out with carbon dioxide, resulting in the calcium carbonate crystals as fillers.

3. The method according to claim 1 or 2, characterized in that the loading process (2) also attaches fillers to the pulp fibers.

4. The method according to claim 1, 2 or 3, characterized in that the centrifugal forces are generated in at least one hydrocyclone (9).

5. The method according to any one of the preceding claims, characterized in that at the inlet in the hydrocyclones (9) a consistency of less than 3% is set.

6. The method according to claim 5, characterized in that at the inlet into the hydrocyclone (9) a consistency of less than 1, 3%, preferably less than 0.8%, is set.

7. The method according to any one of the preceding claims, characterized in that at the hydrocyclone (9) a Rejektstrom (11) is withdrawn continuously, whose size corresponds to 5 - 20 vol% of the feed stream to the hydrocyclone.

8. The method according to claim 1, 2 or 3, characterized in that the centrifugal forces are generated in at least one centrifuge.