Process for treating a fibrous material suspension using...

Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste

Reexamination Certificate

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C162S055000, C162S261000, C209S165000, C210S259000, C210S703000

Reexamination Certificate

active

06183595

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
The present invention claims priority under 35 U.S.C. §119 of German Patent Application No. 197 28 393.4 filed on Jul. 3, 1997, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process and a facility to remove interfering materials from an aqueous fibrous material suspension with the aid of at least two flotation steps directly or indirectly subsequent to each other.
2. Discussion of Background Information
Processes of the noted type are used to eliminate at least a portion of the undesired solid matter particles suspended in a fibrous material suspension containing fibrous material. It is known that a foam or scum containing the materials to be eliminated is formed in a flotation. A common use of such a process is the preparation of an aqueous fibrous material suspension gleaned from printed recycled paper, in which the printing ink particles are already separated from fibers, so that the ink particles can be floated out. The flotation process described here utilizes the differences between fibrous material and undesired solid matter particles in such a way that the fibrous material remains in the fibrous material suspension, due to its rather hydrophilous character, while the already-mentioned solid matter particles are hydrophobic and reaches the foam with the air bubbles. Alongside the printing ink particles, there are other materials which are hydrophobic and thus can be separated by flotation from the fibrous material. In particular, such materials are adhesives, fine synthetic material particles, and perhaps also resins. Since fibers are separated from contaminations via the flotation process and not all fibrous material parts are sorted out, the term “selective flotation” may be appropriate. The likewise utilized term “flotation de-inking” is generally not only used for the removal of printing ink particles but rather more generally for the selective flotation of contaminations from fibrous material suspensions.
Cleaning procedures with two partial steps, a pre-flotation and a post-flotation and mechanical material treatment in the interim, have had a particularly good effect, such as is
5
described in the subject matter essay “Flotationsdeinking—Grundlagen und Systemeinbindung,” H. Britz, published in the
Wochenblatt für Papierfabrikation
10-1983.
The prior art with respect to flotation procedures for fibrous material suspensions has already advanced quite far. Therefore, solutions exist which are certainly suited for removing a large portion of the interfering material particles by flotation. It is disadvantageous, however, when the spectrum of magnitude of the interfering material particles to be removed is very broad. In such cases, problems frequently appear, since the flotation facilities cannot always encompass the whole spectrum of particle size.
It is known that gas pockets will rise in a fluid against a gravity field. This field of gravity is due to the Earth's gravity and can be intensified significantly. In DE 44 26 159 A1, a procedure is described, in which the fibrous material suspension to be cleaned first reaches a flotation cyclone working with centrifugal force and then flotation cells of conventional construction, which, due to the field of gravity, work essentially alone. The flotation foam of the last-named flotation cells—perhaps also of the flotation cyclone—is cleaned in a further flotation cyclone which forms the secondary phase. This process works with the combination of different flotation steps, but it is not sufficient in some cases to produce a completely white de-inking material.
SUMMARY OF THE INVENTION
The invention therefore is directed to a flotation process which broadens the spectrum of the interfering material particles which have been floated out and an arrangement which performs the process.
At least two partial steps which are optimized to a respective special range of magnitude are arranged subsequent to one another. For example, in one partial step, the smaller particles which are present in the fibrous material suspension are floated out through an optimally predetermined high-intensity flotation device. Thereby, especially printing ink particles can be collected which were bonded to the fibers by oil-based binders. In cases in which a thickening device or washing device fitted with circulating continuous sieves (such as in accordance with DE 30 05 681) follows, such printing ink particles could contaminate the sieves and result in interferences. In addition, with high mechanical stress, such as in a subsequently arranged disperser, ink particles generally tend to become worked into the fibers such that they could then be removed only with great difficulty or even not at all. In both cases, the application of the high-intensity flotation arranged upstream of the disperser can produce effective remedial measures.
Even within the pre-flotation, that is, before the mechanical treatment, larger particles can additionally be removed in a low-intensity flotation. Then, it is advantageous to select the sequences such that the low-intensity flotation can be started to remove the larger particles first. Otherwise, these would have unnecessary gas pockets in the high-intensity flotation, without being removed. Generally, however, this sequence is arbitrary. Similar considerations are also to be made with a two-step post-flotation.
In other cases, in which no such fine particles are present in the fibrous material suspension, which are altered disadvantageously in the mechanical treatment, the pre-flotation can be merely a low-intensity flotation, for example, a pre-flotation that can work in the earth's gravity and the post-flotation can be a strong flotation, e.g., a centrifugal field, a low-intensity flotation, or a combination of high and low intensity flotations.
After the first flotation step, the pre-flotation, the interfering material particles which have not yet been removed from the fibers or which are otherwise fixed are removed mechanically.
Thereby, due to the lack of the already-removed particles, it need no longer be feared that these particles will become smaller or that they will be worked into the fibers and, thus, they are no longer necessary to be removed or at least, not at an increased cost.
Thus, in accordance with the foregoing, an object of the present invention is to provide a process for removing material from an aqueous fibrous material suspension. The process includes subjecting the aqueous fibrous material to a flotation process while under a low-intensity gravitational effect. The material is processed to remove fibers from the aqueous fibrous material and the aqueous fibrous material is subjected to a second flotation process while under a high-intensity gravitational effect. A mechanical processing is performed between the first and second flotation processes.
Another object of the invention includes performing the low-intensity flotation process before the high-intensity flotation process.
A further object of the invention is to remove material from the aqueous fibrous suspension while performing the high-intensity flotation process before the low-intensity flotation process.
Yet another object of the present invention includes performing a pre-flotation step and a post-flotation step corresponding to the low-intensity flotation process and the high-intensity flotation process while the mechanical process is performed between performance of the pre-flotation process and the post-flotation process.
Another object of the present invention is to perform the pre-flotation step following the low-intensity flotation process and performing the post-flotation step following the high-intensity flotation process. Again, the mechanical process being performed between the pre and post-flotation processes.
Another object of the present invention includes the pre-flotation step having both a high-intensity flotation process and a low-intensity flo

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