Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Reexamination Certificate
2000-10-26
2002-11-05
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
C162S208000, C162S289000, C162S297000
Reexamination Certificate
active
06475343
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 199 51 794.0, filed on Oct. 27, 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 for dewatering a fibrous material web, e.g., a paper or cardboard web, in which the fibrous material web is guided through a dewatering zone in which it is at least partially dewatered by being impacted with pressurized displacement gas. Moreover, the present invention relates to a device for dewatering the fibrous material web a dewatering zone in which the fibrous material web is at least partially dewatered by being impacted by pressurized displacement gas.
2. Discussion of Background Information
Water can be removed from a paper web using a differential gas pressure. This process is referred to as displacement dewatering. In this process, the water located in the pores between the fibers is blown out of the bonded-web fabric. In comparison to conventional wet presses in a single- or double-felt roll nip, the finished paper has a higher specific volume at the same dry content as after mechanical dewatering. With the aid of the displacement dewatering process, other important characteristics of the finished fibrous material web, such as bending stiffness, porosity, and opacity, can be positively influenced (J. D. Lindsay: “Displacement Dewatering to Maintain Bulk,” Paperi ja Puu Vol. 74/No. 3/1992). A corresponding device arrangement for the displacement dewatering process has also already been suggested (W. Kawka and E. Szwarcztajn: “Some Results of Investigations on the Equipment for Intensive Dewatering and Drying of Porous Papers,” EUCEPA-79 International Conference, Paper 31, Page 153).
If a membrane is placed over the paper on the side of the gas pressure, a compression of the paper will occur as a result of the decrease in pressure in the membrane. Water is pressed out of the fibers into the pores between the fibers. This water is blown out of the pores by the differential gas pressure. According to the invention, when a membrane is used, a higher dry content is achieved (Kari Räisanen: “High-Vacuum Dewatering on a Paper Machine Wire Section: A Literature Review,” Paperi ja Puu, Vol. 78, No. 3, 1996).
The size of this compression depends on the relationship between the permeability of the membrane and of the bonded-web fabric. With a targeted compression, dry content and specific volume of the finished fibrous material web can be adjusted. In practice, however, the compression of the bonded-web fabric can be controlled only with difficulty because membrane permeability is difficult to change during operation of the production facility. Thus, in the case of otherwise identical process conditions, a certain dry content and a certain volume result at a certain gas pressure.
SUMMARY OF THE INVENTION
The present invention is directed to a process and a device of the type generally discussed above in which the process parameters of the displacement dewatering process can be deliberately adjusted and, correspondingly, the results of the displacement dewatering process, with regard to the dry content achieved and to the paper-related characteristics of the finished product, e.g., specific volume, porosity, surface roughness, and/or the like, can be intentionally influenced.
With regard to the process, the present invention includes impacting the fibrous material web with several gas pressure pulses one after another inside the dewatering zone.
Due to this construction, the bonded-web fabric, which has viscoelastic characteristics, is only compressed to a limited extent. If it is taken into account that the compression of the bonded-web fabric is accompanied by a reduction in flow resistance, it is possible, by making the impact with pressure correspondingly shorter, to prevent the bonded-web fabric from becoming too strongly compressed, which could result in the necessary amount of gas being unable to be pressed through the bonded web fabric.
In a suitable practical embodiment, the fibrous material web is guided through several displacement dewatering units within the dewatering zone.
The level of the pressure of at least one gas pressure pulse is advantageously adjustable, and, more suitably, the pressures of the various gas pressure pulses are adjustable separately from one another. If the fibrous material web is guided through several displacement dewatering units arranged at a distance from one another within the dewatering zone, the prevailing pressures in the various displacement dewatering units are advantageously correspondingly adjustable.
In this way, the amount of compression can be adjusted at least partially by, e.g, the level of the prevailing pressure in the respective displacement dewatering units.
Thus, by an individual control of the gas pressure pulses, the dewatering process can be controlled and characteristics such as dry content, density, porosity, and/or the like can be influenced.
In a suitable practical embodiment, the fibrous material web is guided through the dewatering zone along with the membrane, and the fibrous material web is impacted by the displacement gas through the membrane. In principle, however, the displacement gas dewatering according to the present invention can also occur without such a membrane.
Preferably, the fibrous material web, which is being impacted by displacement gas from one side, is guided through the dewatering zone along with at least one wire or felt belt arranged on the other side of the web.
In principle, it is also possible to guide the fibrous material web through at least one displacement dewatering unit within the dewatering zone whose gas pressure is pulsing, i.e., changes over time, and, preferably, at a certain frequency.
In the device according to the invention, the fibrous material web can be impacted by several gas pressure pulses one after the other within the dewatering zone.
The dewatering devices of the various dewatering units can be different and, e.g., run from top to bottom in an alternating fashion.
On the side of the fibrous material web facing away from the gas pressure, a fabric can be arranged that forms a blocking layer. This blocking layer allows the dewatered fluid through. in only one direction, i.e., from the fibrous material web to the felt (anti-rewetting fabric). The blocking layer can be integrated into the felt.
The present invention is directed to a process for dewatering a fibrous material web. The process includes guiding the fibrous material web through a dewatering zone, and directing a plurality of gas pressure pulses of a pressurized displacement gas one after the other onto a surface of the fibrous material web within the dewatering zone.
In accordance with a feature of the instant invention, the fibrous material web can include one of a paper and a cardboard web.
Further, a plurality of displacement dewatering units may be arranged within the dewatering zone at a distance from each other, and the process can further include guiding the fibrous material web through the plurality of displacement dewatering units. The. plurality of dewatering units arranged at a distance from each other may be sequentially arranged in a web travel direction. The process can also include adjusting-the pressures in the plurality of dewatering units.
According to another feature of the present invention, the process may include adjusting a pressure level of at least one of the plurality of gas pressure pulses. The process can also include separately adjusting pressure levels of the plurality of gas pressure pulses.
In accordance with still another feature of the invention, the process can further include guiding the fibrous material web through the dewatering zone along with a membrane, and directing the plurality of gas pulses onto the surface of the fibrous material web through the membrane.
According to a further feature of the instant inventi
Beck David
Begemann Ulrich
Böck Karl Josef
Dahl Hans
Elenz Thomas
Chin Peter
Greenblum & Bernstein P.L.C.
Lopez Carlos N.
Voith Sulzer Papiertechnik Patent GmbH
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