Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
2000-01-18
2002-12-10
Lu, Jiping (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S446000, C034S454000, C162S198000, C162SDIG006, C162SDIG004
Reexamination Certificate
active
06490813
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 01 400.0, filed on Jan. 15, 1999, 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 processes and the corresponding devices for drying and smoothing a web of fibrous material, particularly a paper web, in a machine for manufacturing and/or finishing such a web, including at least one drier section in which the fibrous material web is conducted through a plurality of heated cylinders and a calendar with a number of smoothing nips.
2. Discussion of Background Information
In order to achieve a moisture cross-profile which is as uniform as possible, fibrous material webs have typically been subjected to intense drying and then moistened again at the end of the drying process. This requires a great deal of energy and long dryer sections.
Conventional SC papers achieve a dry content of, e.g., 97-98% at the end of the dryer section, given a good moisture cross-profile of 2 sigma of approximately 0.15-0.3%. With the application of moisture at the end of the dryer section, the dry content here is reduced to 91-93%. After the paper roll has experienced a “maturation time,” during which the moisture content equalizes itself over the thickness of the paper, the paper is fed to a calendar.
To make the manufacturing process more effective, however, there is a growing interest in allowing the calendering process to immediately succeed the drying process. With the elimination of the above-mentioned “maturation time,” however, the moisture cross-profile of the fibrous material web worsens, particularly at high speeds.
Here, the moisture cross-profile measured at the end of the dryer section is used to control the treatment device at the end of the dryer section and is also used, if need be, to control any steam-blowing boxes present in a pressing section positioned in front of the dryer section. This method is not only imprecise, but is also associated with long reaction times, which in turn increases the number of rejects.
SUMMARY OF THE INVENTION
The present invention therefore provides for a process for drying and smoothing fibrous material webs. The invention also provides for devices for performing the process. Moreover, the invention allows for calendering to occur immediately following the drying process, particularly at high speeds, while guaranteeing an optimal moisture cross-profile.
The process provides for the fibrous material web in the dryer section to be dried to a dry content of at most approximately 93% and, in the dryer section, the moisture cross-profile of the fibrous material web is influenced a number of times and/or the moisture distribution is made as uniform as possible over the thickness of the fibrous material web by moistening or drying at least one side of the fibrous material web at a plurality of points during the drying process. A jet humidifier or a steam blow box may be used to add the moisture to the web and this device may be located anywhere along the dryer section. Preferably, the influencing device is located towards the end of the dryer section. Moreover, a dryer section having a beginning, middle, and end section should have at least one influencing device in the end section and one or more such devices in the beginning and middle sections.
A significant savings in energy can be achieved by limiting the dry content of the fibrous material web in the dryer section, which preferably will equal a maximum of approximately 91%.
The assurance of a good and uniform moisture cross-profile, as viewed crosswise to the fibrous material web, is achieved with the treatment of the fibrous material web at a plurality of points within the dryer section.
Furthermore, a relatively uniform moisture distribution over the thickness of the fibrous material web during the drying process is advantageous in that limited moistening or drying at the end of the dryer section is sufficient. Consequently, achieving a good moisture cross-profile also does not require excessive drying.
The invention allows at least the moisture distribution over the thickness of the fibrous material web and/or the moisture cross-profile in the first two thirds of the dryer section to be influenced. It is most important for the influencing device (e.g., a jet humidifier or a steam blow box) to be at least applied in the last third of the dryer section. An additional device can also be located between the dryer section and the calender. In agreement with this suggested configuration of the points of influence, but also independent of them, it can be advantageous for influence to be exerted at a moisture content of between approximately 50% and 15%, preferably between approximately 25% and 15%, and, furthermore, at a moisture content of between approximately 20% and 8%, preferably between approximately 15% and 8%.
As a result of controlling good moisture distribution, and/or a good moisture cross-profile at the end of the dryer section, it is possible for the fibrous material web to pass through the dryer section and the calender at a speed of more than approximately 1200 m/min, preferably more than approximately 1500 m/min. It is of special advantage here for the fibrous material web to be heated and to be pressed and steamed across the width of the web in a manner that permits control according to zone.
The intensity of moistening or drying should be adjustable at several points, so as to influence the moisture cross-profile according to zones across the width of the fibrous material web. In each case, the zones should be adjusted on the basis of the subsequent measurement of the moisture cross-profile. The zone widths should be as small as possible and less than approximately 50 mm, preferably less than approximately 25 mm.
The corresponding device provides for at least one influencing device to be assigned to the fibrous material web in at least one of the first two thirds of the dryer section, as well as in the last third of the dryer section, and in the area between the dryer sections and the calender; and/or that at least one influencing device is assigned to the fibrous material web in an area in which it has a moisture content between approximately 50% and 15%, preferably between approximately 25% and 15%, and in at least one area in which it has a moisture content between approximately 20% and 8%, preferably between approximately 15% and 8%. As an end result, at least two influencing devices are employed, i.e., one in the end section and another at any location described above.
To assure as fine a water distribution as possible, the influencing devices (i.e., jet humidifiers) for moistening, particularly in the last third of the dryer section, should spray water on the fibrous material web with as small a droplet size as possible, in range of less than approximately 100 &mgr;m, preferably less than approximately 80 &mgr;m.
Furthermore, the quotient of the length of the fibrous material web between the last point at which the moisture distribution over the thickness of the web is influenced and/or the moisture cross-profile is influenced, particularly by moistening, and the first smoothing nip of the adjacent calender divided by the speed of the fibrous material web should amount to at least approximately one second. This provides a minimal penetration time and allows the sprayed water to penetrate the fibrous material web up to the beginning of the smoothing process.
Assigned to the influencing devices here are moisture cross-profile measuring units which help control the influencing devices.
To assure a quick reaction time, or optimal control, each influencing device should have a moisture cross-profile measuring unit assigned to it whenever possible, preferably positioned after it in the direction of flow.
It is also possible to provide several moisture cross-profile measuring units and to assign one or two influencing devices to each moistur
Greenblum & Bernstein P.L.C.
Lu Jiping
Voith Sulzer Papiertechnik Patent GmbH
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