Processes for paper manufacture, useful for incorporating paper waste requiring a basic treatment into paper products

Abstract

Processes for manufacturing a paper product from cellulose pulp, part of which comes from a broke and part of which comes from a fresh pulp are provided. The processes involve first redissolving in a broke pulper, with stirring and in an alkaline medium, cellulose fibers contained in said broke to form a broke pulp. Next, the broke pulp is brought to a concentration and a pH close to that characteristic of the fresh pulp by (1) diluting said broke pulp with a white water and (2) acidifying said broke pulp by injecting carbon dioxide into said broke pulp after the broke pulp has left the broke pulper and before admixing said broke pulp with said fresh pulp. Then the broke pulp is admixed with the fresh pulp to form a pulp mixture and the pulp mixture is dewatered to form a paper product and a white water.

Description

[0001] (I) Field of the Invention[0002] The present invention relates to improved processes for manufacturing paper products. In particular, the invention relates to processes that incorporate paper waste, which requires a basic treatment, and particularly "brokes" into paper products.[0003] (II) Description of the Related Art[0004] The papermaking process comprises two successive and separate parts. The first part is the preparation of the paper pulp. In this part, the paper pulp is manufactured from various fibrous materials containing cellulose (such as wood and / or annual plants) using chemical agents and / or mechanical actions.[0005] The second part is the manufacture of the paper. The term "paper" denotes a paper product, including but not limited to paper for use in graphics, packaging paper, domestic paper, various special papers, as well as boards and other such products. The terms "paper" and "paper product" will be employed interchangeably in the rest of the text.[0006] The...

AI Technical Summary

Benefits of technology

[0047] By injecting the carbon dioxide into the broke pulp after the broke pulp has left the broke pulper and before admixing the broke pulp with the fresh pulp, the invention avoids certain disadvantages associated with injecting carbon dioxide directly into the broke pulper, such as unsatisfactory mixing of the carbon dioxide with the medium to be treated. Such approach consumes time and carbon dioxide for a mediocre result.

[0057] In an embodiment, the processes comprise injecting judicious amounts of carbon dioxide directly into the white water of the process serving for diluting the pulp coming from the prior treatment of the broke, makes it possible to achieve all the advantages enumerated above with, in addition, increased efficiency and operational simplicity and flexibility which are also increased, something which constitutes an additional advantage of the present invention over the prior art. In particular, it makes it possible, using different points of introduction of white water into the circuit, to jointly ensure that the pulp consistency and the pH are the best suited for each step of the broke treatment, this being so both for continuous treatments and for batch treatments, whatever the temperature in the pulper 15.

[0059] The introduction of CO.sub.2 into the broke treatment circuit will be done while taking into account the well-known effect of the pH on cellulose fibers. Indeed, it proves to be particularly advantageous to carry out the deflaking and / or mechanical slushing operations before having lowered the pH too much, so as not to weaken the fiber too much, made weaker by a more acid medium. This is because in a more acid medium the fibers become harder and brittle. Refining in a more acid medium results in an excess of brittle fibers, resulting from shorter fibers, and generates a considerable amount of fines. However, the energy needed for deflaking decreases proportionally with the drop in pH.

[0113] In addition, the defiberizing is inevitably accompanied by a fragmentation of certain contaminants, something which will reduce the effectiveness of their removal. The technological trend, mainly with regard to pulpers operating at medium concentration (15%), in the de-inking field is directed toward meeting the objectives of reducing contaminant fragmentation, of saving energy and of increasing the reactivity of the chemicals used.

[0122] Because of these dilutions with water at pH values often greater than 7 and because of the optional addition of chemicals such as sodium hydroxide (the role of which is especially to hydrate and swell the fiber, thus destroying the bonds, and thereby making it possible to reduce the subsequent mechanical slushing which damages the fibers) the pH rises to values greater than those of the fresh pulp.

Problems solved by technology

However, none of these processes propose or suggest the use of carbon dioxide as a pH regulator in the broke circuit.

However, it provides no solution to the problem of achieving fine and flexible pH regulation, tailored to the constraints of the various steps of the broke treatment that is easy to implement, both in continuous broke treatments and in batch broke treatments, and at any temperature in the pulper.

Moreover, the addition of carbon dioxide into the pulp in the pulper as described in EP 0,911,443 impairs the precision of the regulations.

These conditions do not allow satisfactory mixing of the carbon dioxide with the medium to be treated.

The acidification thus consumes time and carbon dioxide, for a mediocre result.

In addition, it is limited to batch broke treatments.

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