Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
1999-03-23
2001-02-20
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S460000, C034S463000, C034S507000
Reexamination Certificate
active
06189237
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a procedure and device for drying a web, e.g., a paper or tissue web, in motion in a machine for producing or converting the web.
2. Discussion of Background Information
Guiding the web over rotating, heated cylinders for drying is known in the art. Heating the web in this manner releases moisture in the form of steam. As the dry content of the web increases, however, the capacity of the web to outwardly release steam from the inside decreases.
This evaporation can be intensified by guiding the web over vacuum guide rolls. Generally such guide rolls are composed of a perforated roll sleeve having a negative pressure created inside either directly, through connection with a negative pressure source, or indirectly, through suctioning or vacuuming of an area of the perforated roll sleeve that is not covered by the web.
In this manner, the negative pressure draws the steam out of the web. However, creating the requisite negative pressure, particularly at a high level, is associated with significant technical expense and expenditure of energy.
SUMMARY OF THE INVENTION
The present invention, therefore, provides a process and device for drying a web in a manner that improves the carrying off of steam from the web relatively simply.
According to the present invention, a blanket of compressed air is created on one side of the web that presses the steam of the web toward a side of the web facing away from the created blanket of compressed air. The blanket of compressed air may be created between the web and an air-tight guide element so that a boundary layer of air carried along with the web, i.e., entrained air, is accumulated via a damming effect by the guide element. The pressure in the blanket of compressed air can attain a value of, e.g., between approximately 0.01 and 0.2 bar.
This manner of creating compressed air, while relatively simple, may be very effective with regard to transporting steam. The process can be further supported in that the side of the web facing away from the blanket of compressed air may be subjected to a vacuum. In this manner, a relatively low degree of negative pressure can be sufficient.
For support, the web, i.e., the surface or side of the web facing away from the created blanket of air, may be guided on an air-permeable support element. This support element may be formed by at least one air-permeable belt that moves with the web, e.g., a press felt of the press or drainage section or a drying sieve (screen) of the drying section of a machine for producing and/or converting the web. Further, the support element may be formed as a guide roll having a perforated or grooved roll sleeve.
In either case, the surface of the web facing away from the created blanket of compressed air can be subjected to a vacuum by positioning a suction device on or adjacent to the support element. In such a combination, the air-permeable belt can also be guided around the guide roll. According to this arrangement, the belt guides the web to and from the guide roll.
The damming effect with respect to the boundary layer of air and, therefore, also to the pressure in the blanket of compressed air can be increased by reducing the distance between the web and the guide element, particularly the distance between the downstream end of the guide element and the web. Thus, the guide element may form a feeding wedge with the web that tapers down in the travel direction of the web.
The distance between the web and the guide element can be, e.g., between approximately 0.01 and 20 mm, particularly between the downstream end of the guide element and web. Depending on the basis weight, moisture, dry content, porosity, type of web and/or machine speed, the distance between the web and the guide element, in the direction in which the web travels, may be adjustable, particularly at an upstream or start end and/or the downstream end. Further, the guide element may also be positionably adjustable during operation of the machine.
Moreover, the device in accordance with the features of the present invention may automatically adjust the distance as a balance between the pressure in the blanket of compressed air and a spring resistance. In this manner, the distance may be dependent mainly on machine speed.
The guide element or elements may have a length in the direction of web travel of, e.g., between approximately 0.05 and 1.50 m, and preferably approximately 0.2 and 0.5 m. The guide elements can be formed by an at least partially fixed plate and/or a rotating continuous belt that preferably has a contoured surface for greater air drag-in. Further, the device may further enhance the drying effect if the guide element is heated.
Moreover, to increase the pressure in the blanket of compressed air, additional compressed air, particularly heated compressed air, can be blown between the guide element and the web. The additional compressed air may be preferably blown in from the start end area of the guide element with respect to the web travel direction.
For limiting or sealing the blanket of compressed air, blast nozzles, brushes, or similar devices, may be positioned on the sides of the guide element that extend in the web travel direction and are positioned opposite each other cross-wise to the web travel direction. In this manner, too sharp a decrease in the pressure of the blanket of compressed air toward the edges of the web may be prevented.
Alternatively, or in combination with the additional compressed air, a coating device for providing a coating in a dry or liquid form can be introduced into the blanket of compressed air. For example, calcium carbonate, titanium dioxide, silicate, adhesives, and starches may be particularly suitable for coating the surface of the web.
Accordingly, the present invention is directed to a process for drying a moving web. The process includes vaporizing moisture in the web, creating a blanket of compressed air along a first surface of the web, and the blanket of compressed air directing the vaporized moisture in a direction from the first surface toward a second surface of the web that faces away from said blanket of compressed air.
In accordance with another feature of the present invention, the process may include suctioning the second surface of the web.
In accordance with another feature of the present invention, the pressure in the blanket of compressed air may lie within a range between approximately 0.01 to 0.2 bar.
In accordance with still another feature of the present invention, a guide element may be positioned adjacent to the web to create said blanket of compressed air, and the process may further include adjusting a distance between at least a downstream end of the guide element relative to a web travel direction.
In accordance with a further feature of the present invention, the process may further include creating a second blanket of compressed air along the first surface of the web downstream from the blanket of compressed air relative to a web travel direction.
In accordance with a still further feature of the present invention, the process may further include supporting the second surface of the web on an air-permeable support element. The vaporized moisture may be directed toward the support element.
In accordance with still another feature of the present invention, the process further includes supporting the second surface of the web on a suction guide roll, said blanket of compressed air directing the vaporized moisture toward the suction guide roll, and suctioning the vaporized moisture directed toward the suction guide roll.
In accordance with another feature of the present invention, a guide element may be positioned adjacent to the web for creating said blanket of compressed air, and the process may further include blowing additional compressed air in a web travel direction into a region between the guide element and the web.
In accordance with still another feature of the present invention, a guide element may be positioned adjacent to the web for cr
Mayer Roland
Steiner Karl
Greenblum & Bernstein P.L.C.
Voith Sulzer Papiertechnik Patent GmbH
Wilson Pamela
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