Process and flotation device for the removal of intereering materials from an aqueous fiber pulp suspension

Abstract

The process is designed for the flotation of interfering materials from an aqueous fibrous pulp suspension and is in particular used in the processing of printed or used paper that is otherwise contaminated. The separation of gas bubbles of the suspension occurs in a flotation layer that has a maximum thickness of approximately 100 mm. The process also achieves good flotation results in fibrous pulp suspensions that have a fiber pulp content significantly larger than 1 % by weight, for example around 2% by weight. A flotation apparatus is provided for performing the flotation process. The apparatus includes a flotation vessel, an inlet, an outlet, and a skimmer device.

Description

[0001] The present application is a continuation of U.S. patent application Ser. No. 08 / 115,672 filed Jul. 15, 1998, which claims the priority under 35 U.S.C. 119 of German Patent Application No. 197 30 464.8, filed on Jul. 16, 1997, the disclosures of which are expressly incorporated by reference herein in their entireties.[0002] 1. Field of the Invention[0003] The invention relates to a process and apparatus for the removal of interfering materials from an aqueous fiber pulp suspension.[0004] 2. Discussion of Background Information[0005] Processes of the aforementioned type are used in order to remove at least a portion of the interfering pulp particles suspended in a fibrous pulp suspension containing fiber pulp. It is common knowledge that a foam or floating slurry, containing the material to be removed, is created in a flotation process. A typical case of application of such a process is the processing of aqueous fibrous pulp suspensions that are produced from printed used pape...

AI Technical Summary

Benefits of technology

[0008] By the present invention, the difficulties, caused by the high viscosity of the suspension, can be overcome. The gas bubbles, loaded with interfering materials, have an increased resistance while reaching from the suspension into the flotation foam by following their tendency to rise. However, because of the fact that the flotation process is executed with a relatively thin flotation layer, the gas bubbles only have to travel a very short distance. In embodiments of the process in accordance with the invention, the gas bubbles' tendency to rise can be enhanced by applying a gravity field which is greater than earth's gravity. Another possibility makes provisions to accelerate the rise of the gas bubbles with the aid of impulses or vibrations.

[0018] A further feature is to create a micro-turbulence in the suspension prior to the initial processing and to accelerate the suspension to at least twice the average flow velocity during the entry into the flotation layer.

Problems solved by technology

However, the effect weakens when the amount of fibers in the suspension is relatively high, for example 2 %, instead of the conventional amount of around or below 1 %.

In such cases problems often occur since the resistance for the gas bubbles is already high with a higher fiber content, thereby making it difficult to separate the suspension.

However, because of the fact that the flotation process is executed with a relatively thin flotation layer, the gas bubbles only have to travel a very short distance.

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