Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste
Reexamination Certificate
2001-06-19
2002-06-25
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Waste paper or textile waste
C162S055000, C209S728000, C210S221200, C210S260000, C210S928000
Reexamination Certificate
active
06409880
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus and process for removing impurities, and more particularly, to an apparatus and process for removing fine impurities from a fibrous suspension.
2. Discussion of Background Information
Fibrous suspensions, particularly those obtained from recycled paper which are intended for paper production, contain undesirable attendant materials, also referred to as “interfering materials,” which must be removed in the preparation system. The removal of these interfering materials is generally performed in various steps since a fibrous suspension purification in a single process step is rarely successful.
Wet straining processes have turned out to be particularly effective for the removal of fine impurities. In such processes, the suspension is conveyed into a straining device and is divided into at least two portions, an “accepts” portion, i.e., the materials that have passed the wire, and a “rejects” portion, i.e., the materials rejected due to their size. Generally, in the parlance of paper makers, such wet straining processes are known as “sorting.” It is also known to subject the rejected materials, i.e., the rejects portion, to one or more additional subsequent straining steps. This process is known as “multistep sorting.” Multistep sorting can be carried out at various points of the paper stock preparation. Generally, the later the sorting occurs during the process, the finer the wire openings that can be used in the process. Examples of multistep wet straining are demonstrated in the scientific paper “Sortierung von Altpapierstoff zur Herstellung von graphischen Papieren” [Sorting of Recycled Paper Stock for the Manufacturing of Graphic Papers] by R. Rienecker from the Wochenblatt für Papierfabrikation [Weekly for Paper Making] No. 23/24, 1997, pp. 1149 to 1159.
Although a large number of different systems are already known and used for purifying paper stock suspensions, these systems are often unsuccessful in removing all interfering impurities from the suspension. In particular, very fine, adhesive impurities, which often cause great difficulties in the production of paper, even in small quantities, can only be removed at great expense, if at all.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and process for removing fine impurities from a fibrous suspension. The apparatus comprises a dissolution device, a pre-purification device, a wet straining device, and a flotation device. The wet straining device comprises at least two sorting devices installed in sequence, each sorting device having a wire for separating the fibrous suspension into an “accepts” portion and a “rejects” portion. The flotation device is adapted to purify the “accepts” portion of at least one sorting device, and further separates the fibrous suspension into an “accepts” portion and a “rejects” portion.
The flotation device may be further adapted to purify the “accepts” portion of the last of the at least two sorting devices. Additionally, the flotation device may be adapted to receive the “accepts” portions of the last two of the at least two sorting devices.
The apparatus may also comprise a finishing device adapted to receive at least one “accepts” portion of the wet straining device. Furthermore, the apparatus may be adapted to receive at least one “accepts” portion of the flotation device.
The pre-purification device may be adapted to remove ink particles, and may remove these ink particles by flotation
Additionally, the sorting devices of the wet straining device may be embodied as closed pressure sorters. The pressure sorters may each be equipped with wires having free wire openings, the free wire openings having slits with a width of between about 0.08 and 0.5 mm. Alternatively, the free wire openings may be holes with a diameter of between about 0.8 and 3 mm.
The flotation device may additionally comprise a selectively functioning flotation cell.
The process for removing fine impurities from a fibrous suspension comprises the steps of subjecting the fibrous suspension to a dissolution process, subjecting the fibrous suspension to a pre-purification process, and purifying the fibrous suspension in a wet straining process. At the wet straining process, at least two sorting devices are installed in sequence, each sorting device having a wire for separating the fibrous suspension into an “accepts” portion and a “rejects” portion. The wet straining process comprises introducing a “rejects” portion rejected at the wire of a preceding sorting device into the subsequent sorting device until a last subsequent sorting device has been reached, conveying the “rejects” portion out of the process, and conveying the “accepts” portion to a flotation process. The “accepts” portion is purified by at least one flotation process, which further separates the fibrous suspension into an “accepts” portion and a “rejects” portion, the “rejects” portion containing a majority of the impurities of the fibrous suspension, and the “accepts” portion containing a majority of the fibers of the fibrous suspension.
The “accepts” portions of the sorting devices may contain the highest percentage of interfering materials that can be floated and may be purified in the flotation process.
Additionally, the “accepts” portion of the last subsequent sorting device may be purified in the flotation process. Alternatively, the “accepts” portions of the last two steps of the wet straining process may be supplied to the flotation step process.
The “accepts” portions of the wet straining process that are not purified in the flotation process may also be combined and supplied directly to a finishing process. Also, the “accepts” portion of the flotation process may be supplied to the remaining “accepts” portions of the wet straining process.
The pre-purification process may remove ink particles, and may remove these ink particles by flotation.
The sorting devices of the wet straining process may be closed pressure sorters. These pressure sorters may be equipped with wires having free wire openings having slits with a width of between about 0.08 and 0.5 mm. Alternatively, the free wire openings may be holes with a diameter of between about 0.8 and 3 mm.
At the beginning of the wet straining process, the dry matter content of the fibrous suspension may be set to a value of between about 0.6 and 2.5%, or alternatively, may be set to a value of between about 2 and 4%.
The flotation step may be performed in a selectively functioning flotation cell.
The suspension to be purified may further contain adhesive particles.
Before the flotation step, the suspension may be subjected to a chemical treatment in which surface activity of the interfering materials is increased.
The fibrous suspension may be dispersed before the flotation process or alternatively, before the wet straining process. A specific work of at least 20 kWh/to may be transmitted to the fibrous suspension during the dispersion of the fibrous suspension.
The invention also provides for a process for removing fine impurities from a fibrous suspension, comprising conveying the fibrous suspension to at least one sorting device, separating the fibrous suspension using the at least one sorting device into an accepts portion and a rejects portion, finishing at least some of the accepts portion leaving the at least one sorting device using a finishing device, separating at least some portion of the rejects portion leaving the at least one sorting device using at least one last sorting device into an accepts portion and an rejects portion, separating at least some portion of the accepts portion leaving the at least one last sorting device into an accepts portion and a rejects portion using a flotation device, and finishing at least some portion of the accepts portion leaving the flotation device using the finishing device.
At least one intermediate sorting device may be arranged between the at least one sorting device and the at least one last sorting device, and the proce
Kemper Martin
Wiese Horst
Greenblum & Bernstein P.L.C.
Nguyen Dean T.
Voith Sulzer Papiertechnik Patent GmbH
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