Classifying – separating – and assorting solids – Fluid suspension – Liquid
Reexamination Certificate
1998-07-15
2001-05-08
Lithgow, Thomas M. (Department: 1724)
Classifying, separating, and assorting solids
Fluid suspension
Liquid
C209S170000, C162S004000
Reexamination Certificate
active
06227374
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The present application claims the priority under 35 U.S.C. 119 of German Patent Application No. 197 30 464.8, filed on Jul. 16, 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 apparatus for the removal of interfering materials from an aqueous fiber pulp suspension.
2. Discussion of Background Information
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 paper, whereby the ink is already dissolved from the fibers so that it can be floated out. The flotation process described here utilizes the differences between the fibrous pulp and the undesirable solid particles such that the fibrous pulp, due to its hydrophilic nature remains in the fibrous pulp suspension, while the described solid particles exhibit hydrophobic behavior and therefore end up with the air bubbles in the foam. Aside from the ink particles there are also a large number of additional materials that are hydrophobic and are able to be separated from the fibrous pulp by flotation. Such materials are in particular adhesives, fine synthetic material particles, and possibly also resins. When the fibers are to be separated from contamination, i.e. not all solid particles are to be sorted out, a selective flotation process is performed. The term “flotation de-inking”, also used, is generally not only used for the removal process of ink particles, but also used in a more general sense for the selective flotation of contamination of fibrous pulp suspensions.
The state of the art in regards to flotation processes for fibrous pulp suspensions is already at a very advanced state. There are thus solutions which are quite suitable in removing a large portion of the solid particles by flotation. 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. Higher pulp densities, on the other hand, are desirable in order achieve a higher throughput.
SUMMARY OF THE INVENTION
The aim of the invention is therefore to create a flotation process in which good cleaning results can be achieved even when the suspension for such processes has a relatively high fibrous pulp content.
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.
Thus, an aspect of the invention is to provide a process for removing interfering materials from a fibrous pulp suspension by generating air bubbles in the form of a gas, collecting the interfering materials by using the gas bubbles, and removing the interfering materials with a flotation foam. The fibrous pulp suspension and the gas bubbles are introduced into a flotation layer having a maximum thickness of approximately 100 mm so as to separate the gas bubbles and the fibrous pulp suspension.
Another aspect of the process is to provide a flotation layer with a thickness of approximately 50 mm.
A feature of the process is to provide the gas bubbles as air bubbles, in the alternative, the bubbles may be provided by a gas that is lighter than air.
Another feature of the process is to directly add the gas bubbles to the flotation layer of the suspension and to admix the bubbles prior to the time the fibrous pulp suspension enters the flotation layer.
Another aspect is to transmit vibrations to the flotation layer and to transmit the vibrations by shaking at least a part of the flotation element that is in contact with the flotation layer. Another feature is to transmit the vibrations by using an agitating element, or hydraulic and/or pneumatic impulses.
Another concept of the process is to clean a fibrous pulp suspension that has a fiber pulp content of approximately 2% by weight in the flotation layer and to dilute the pulp suspension after the addition of the bubbles and transform the suspension in the flotation layer and to add bubbles of different sizes to the flotation layer so that the bubble size varies in the direction of flow of the suspension. A feature is to also vary the size of the bubbles in a rising direction of the bubbles.
Another feature is to create a local turbulence in a separation region of the flotation layer, the separation region being between the suspension and the flotation foam.
A further aspect of the process is to provide a flotation procedure wherein the flotation layer extends approximately 150 mm in a flow direction of the flotation layer.
A feature of the invention is to subject the suspension to an initial processing in which the suspension is fed at a height that is greater that a thickness of the flotation layer and to provide a flotation layer that extends in its flow direction a distance of between approximately 1 mm and approximately 500 mm.
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.
Another characteristic of the invention is to divert the cleaned suspension layer immediately downstream of the cleaning process and to perform the separation in a gravity field that is greater than earth's gravity while yet another aspect of the invention is to perform the separation in a flotation cyclone.
Still a further aspect is to add some of the gas bubbles to the suspension before entry into the flotation cyclone and add additional bubbles afterwards and to perform the process in a centrifuge.
A feature of the invention is to provide an apparatus in which the flotation process is performed. The apparatus includes a flotation vessel which receives the suspension to be cleaned, an inlet for receiving the suspension and an outlet for discharging the cleaned suspension. A skimmer element is provided for separating flotation foam, created in the flotation process, from the suspension. The skimmer separates a flotation chamber receiving the suspension by setting a filling height that does not exceed approximately 100 mm.
An aspect of the invention is to provide an apparatus for carrying out the flotation process is also to provide a flotation chamber that is substantially planar and to provide the chamber with a corrugated bottom wall so that the corrugations extend perpendicular to a flow direction of the fibrous pulp suspension and to supply gas by way of pipes located in the bottom wall so ass to add gas bubbles to parts of the flotation layers of the fibrous pulp suspension, the gas bubbles being added to the flotation layers having a predetermined depth.
Another aspect is to provide the apparatus with an incline extending in the direction of the skimmer and to provide the gas supply box so that it extends along the flotation chamber at least over a portion of a flow pat
Britz Herbert
Gommel Axel
Holik Herbert
Kemper Martin
Kriebel Almut
Greenblum & Bernstein P.L.C.
Lithgow Thomas M.
Voith Sulzer Papiertechnik Patent GmbH
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