Classifying – separating – and assorting solids – Fluid suspension – Liquid
Reexamination Certificate
2000-02-03
2001-08-28
Lithgow, Thomas M. (Department: 1724)
Classifying, separating, and assorting solids
Fluid suspension
Liquid
C209S170000, C210S221200, C162S004000
Reexamination Certificate
active
06279749
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 199 05 439.8, filed on Feb. 10, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process and apparatus for removing solids from an aqueous fiber suspension, e.g., a paper fiber suspension, with the aid of gas bubbles. The removed solids are collected in a flotation foam, and discharged as rejects. In this way, the fiber suspension is purified to be constituted by accepted stock suspension.
2. Discussion of Background Information
Processes of the type similar in general that discussed above are used to remove at least a part of the solid particles suspended in a fibrous material-containing suspension. As is known in flotation, foam or scum is formed which contains the materials to be removed. A typical application of this type of process produces an aqueous paper fiber suspension from printed waste paper in which ink particles have already been removed from fibers so that they can be floated out. Thus, this flotation process exploits the differences between fibrous material and undesirable solid particles so that the fibrous material, which is hydrophilic, remains in the fibrous material suspension while the solid particles to be removed, which are hydrophobic, therefore, end up in the foam along with the air bubbles. In addition to ink particles, there are a multitude of other hydrophobic substances that can be removed from the fibrous material via flotation. These substances include, e.g., glues, fine plastic particles, and possibly also resins. If one simply wanted to separate fibers from impurities via flotation, i.e., not all solid particles are to be sorted out, then such a process is referred to as “selective flotation” or “flotation de-inking.” As a rule, “flotation de-inking,” is not only utilized for the removal of ink particles, but is also generally used for the selective flotation of impurities out of fibrous material suspensions.
The prior art with regard to flotation processes and device for fibrous material suspensions has been extensively developed. Therefore, there are embodiments which are quite suitable for removing a large part of the solid particles via flotation. An important aspect in processes of this type, however, involves which composition and properties are achieved in the flotation foam. Thus, it is desired to remove the flotation foam from the flotation system in the most dewatered form possible, so that removed foam contains the greatest possible quantity of the floated-out impurities and the lowest possible quantity of paper fibers. In general, the flotation foam is collected above the suspension involved in the flotation and is removed, e.g., laterally via a foam weir or vertically upward via a suction device. As a result, dewatering, i.e., drainage, of the flotation foam takes place.
SUMMARY OF THE INVENTION
The present invention provides a flotation process for effectively removing certain solids from the fibrous material suspension and further dewatering of the flotation foam produced, without significantly increasing the cost.
In particular, the present invention includes laterally removing the flotation foam from the fiber suspension, e.g., a paper fiber suspension, in a drainage section, collecting a part of the fluid contained within the flotation foam in the drainage section and removing the fluid.
By virtue of the fact that, according to the instant invention, the flotation foam is laterally removed or obliquely upwardly removed in a special drainage section, the flotation foam travels along a relatively long path in which a part of the fluid contained within the flotation foam can be collected and drained away. As a result, the foam can be dewatered in a simple manner, which is advantageous to known devices because the expressing of water from greasy flotation foam is very expensive. The fluid, generally dirty water, comes out of the foam, and, after a short downward section, reaches, e.g., a wall that adjoins the bottom of the drainage section so that the fluid can be drained away against this wall. This arrangement can also effectively prevent an undesirable pushing back or damming up of subsequent flotation foam. Another important advantage of the present invention lies in the fact that, if necessary, it is easily possible to drain the removed fluid from the flotation container. In general, this fluid may be more heavily encumbered with impairing solids than the suspension itself.
There are a number of possibilities for treating the draining fluid. For example, the fluid can be removed from the flotation container and supplied to a special purification or other re-use device. Alternatively, the fluid can flow directly back into the suspension in which the flotation is carried out. It would be advantageous if the paper fibrous suspension in the flotation container were not swirled so intensely that the draining fluid could get into the outlet for the purified fibrous material suspension, i.e., the accepted stock. Another possibility lies in bringing the fluid back, together with the paper fiber suspension flowing into the flotation container, in order to subject it to renewed flotation. When the flotation container is closed, the flotation air may nonetheless be aspirated out of the container and conveyed into a ventilation injector. In the process according to the invention, a mixture of air or gas and the returned fluid can be carried out.
The present invention is directed to a process for removing solids from an aqueous fiber suspension in a flotation container that includes a drainage section. The process includes adding gas bubbles to the fiber suspension entering the flotation container, and collecting a flotation foam formed within the flotation container. The flotation foam includes the solids to be removed. The process also includes laterally moving the flotation foam in the drainage section, such that at least a portion of fluid within the flotation foam is drained from the flotation foam, collecting the drained fluid in the drainage section, discharging the drained fluid from the drainage section, discharging the flotation foam as a rejects material, and discharging a purified fiber suspension as an accepted stock suspension.
According to a feature of the invention, the drained fluid may be collected against a wall that adjoins a bottom of the drainage section.
In accordance with another feature of the invention, a flow direction in the drainage section can have an inclination angle between approximately 0° and 80° in relation to the horizontal. Further, the inclination angle can be between approximately 30° and 60°.
In accordance with still another feature of the present invention, the process can further include adjusting an inclination angle of the drainage section relative to horizontal.
The process may further include supplying the drained fluid discharged from the drainage section to the fiber suspension entering the flotation container. The drained fluid can be supplied without special purification. Moreover, the process can include adding gas bubbles the fluid and the fiber suspension entering the flotation container. The flotation container can include an injector, and the process may further include ventilating the fiber suspension with the injector, and aspirating the gas being freed from the flotation foam and the fluid flowing out of the drainagce section with the injector.
According to a further feature of the invention, the process may further include clarifying the drained fluid removed from the drainage section.
In accordance with still another feature of the instant invention, a flow cross section of the drainage section may be one of round and oval.
In accordance with a still further feature of the invention, the flow cross section in the drainage section can decrease in the flow direction of the flotation foam.
Moreover, a length of the d
Gommel Axel
Kemper Martin
Kriebel Almut
Greenblum & Bernstein P.L.C.
Lithgow Thomas M.
Voith Sulzer Papiertechnik Patent GmbH
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