System and method for removing foreign particles from an aqueous fibrous suspension

Abstract

A method and system is used for removing foreign particles, e.g., printing ink particles, from an aqueous fibrous suspension, in particular recovered paper suspension. The method includes dividing the suspension in a fractionation into a fine fraction, in particular short-fiber fraction, and a coarse fraction, in particular long-fiber fraction. Both of the fractions thus formed are then treated in respectively differently operated flotations in order to carry away the foreign particles in the flotation foam. The parameters and apparatuses used of the two flotations can be optimally adjusted thereby to the conditions present in the individual fractions.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 10 2005 021 929.2, filed on May 12, 2005 and German Patent Application No. 10 2005 060 476.5, filed Dec. 17, 2005, the disclosures of which are expressly incorporated by reference herein in their entireties. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The invention relates to a method for removing foreign particles from an aqueous fibrous suspension and, more particularly, to a method for removing foreign particles in a recovered paper suspension with the aid of several selective flotations. [0004] 2. Discussion of Background Information [0005] Methods can be used to eliminate at least part of the undesirable solid particles, e.g., foreign particles, suspended in a paper fiber suspension. A typical method is the treatment of an aqueous fibrous suspension obtained from printed recovered paper, in which suspension of the p...

AI Technical Summary

Benefits of technology

[0010] The invention creates a preparation method with which the most effective possible elimination of the foreign particles can be achieved without excessively high expenditure in terms of equipment and operation being required.

[0011] The method according to the invention has the advantage that the flotations respectively treat only one fraction and can be optimally adapted to the special requirements of these fractions.

[0013] The method is typically applied to recovered paper suspensions. This starting material contains a mixture of different fibers and impurities. Through the fractionation, a smaller proportion of dyes and / or fillers are transferred from this mixture into the coarse fraction, while the fine fraction contains larger amounts of the floatable foreign particles together with the short fibers. In a fine fraction formed in this manner, the flotation conditions are more favorable than in the coarse fraction. That is, the flotation of the fine fraction can yield a good result even, e.g., with higher consistency, while, e.g., the conventional full stream flotation is carried out with a consistency of approximately 1.3%. When the method according to the invention is applied, the fine fraction can be floated at approximately 1.5% and the coarse fraction at approximately 0.9%. In embodiments, a fine adjustment of these consistency values to the conditions and requirements is possible. Other possibilities for influencing the flotation are provided by variations of the chemical metering.

Problems solved by technology

Such methods are very effective but relatively complex, since each partial step contains a complete selective flotation for the entire fibrous paper stock.

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