Drying and gas or vapor contact with solids – Apparatus – Rotary drums or receptacles
Reexamination Certificate
2001-05-29
2003-01-28
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Apparatus
Rotary drums or receptacles
C034S117000, C034S120000, C034S126000, C162S193000, C162S207000, C162S358500, C162S359100
Reexamination Certificate
active
06510623
ABSTRACT:
CROSS REFERENCES TO RELATED APPLICATIONS
This application claims priority on Finnish Application No. 20001307, filed May 31, 2000, the disclosure of which is incorporated by reference herein.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The invention relates to dryer groups in a dryer section of a paper or board machine, and to dryer sections of paper or board machines.
As known from the prior art, in multi-cylinder dryers of a paper machine, twin-wire draw and/or single-wire draw in/are employed, In twin-wire draw, the groups of drying cylinders comprise two wires which press the web, one from above and the other one from below, against heated cylinder surfaces. Between the rows of drying cylinders, which are usually horizontal rows, the web has free and unsupported draws, which are susceptible to fluttering, which may cause web breaks, in particular as the web is still relatively moist and, therefore, has a low strength. Therefore, ever increasing use has been made of said single-wire draw in which each group of drying cylinders comprises—only one drying wire on whose support the web runs through the entire group so that, on the drying cylinders, the drying wire presses the web against the heated cylinder surfaces and, on the reversing cylinders or rolls situated between the drying cylinders, the web remains at the side of the outside curve. Thus, in single-wire draw, the drying cylinders are arranged outside the wire loop, and the reversing cylinders or rolls are arranged inside the loop. One problem with these prior art arrangements is constituted by the cylinders and rolls which are situated outside the wire loop and which get soiled, wherefore it has been necessary to provide them with doctors to keep the surfaces clean.
With increasing speeds of paper machines, the runnability of a paper machine is, of course, also affected by the dryer section, whose length with the prior art multi-cylinder dryers would, at high speeds, also become very long. If it is imagined that a present-day multi-cylinder dryer were used at a web speed of 40 m/s, it would include about 70 drying cylinders, and its length in the machine direction would be about 180 meters. In such a case, the dryer would comprise about 15 separate wire groups and a corresponding number of draws over the group gaps. It is to be assumed that, in a speed range of from 30 to 40 m/s, the runnability of the normal prior art multi-cylinder dryers would not be good because of the open draws, in which connection there may occur web breaks that reduce the efficiency of the paper machine. In a speed range of from 30 to 40 m/s and at higher speeds, the prior art multi-cylinder dryers, then, would also become uneconomical because the investment costs of an excessively long paper machine hall would be high. The dryer sections composed of multi-cylinder dryers are often also very high.
Moreover, in dryer groups of known applications, wires seamed on the machine have to be used because of the closed frame structure. The seam of a wire seamed on the machine may cause a discontinuity in the drying of the web in connection with the drying process. In addition, the seam of the wire seamed on the machine may limit the applied tension of the wire.
Further problems manifested with increased emphasis at high speeds of paper machines, for which problems, at least for all of them, satisfactory solutions have not been found as yet, include the problems of quality related to the requirements of uniformity of the profiles of properties of the paper web both in the machine direction and in the cross direction. Uniformity of the web produced also affects the runnability of the entire paper machine, and it is also an important quality factor of finished paper. Application of high speeds, in particular in wide machines, thus provides ever more difficult problems to be solved, of which problems, the most important ones are runnability and adequate dewatering capacity of the machine at a high speed.
One problem in dryer sections of a paper machine, when conventional dryer sections composed of multi-cylinder dryers are used, is the noise they cause. In addition, when cylinder drying is employed, it is necessary to use steam, which means that the drying cylinders have to be dimensioned to comply with pressure vessel regulations and, furthermore, the hood arranged around the dryer section has to be made to be thermally insulated.
It is known from experience that, if paper is dried one-sidedly, the result is a tendency of curling of the sheet. When paper is dried by means of normal singlewire draw groups from the side of its bottom surface and, if such asymmetric drying is extended substantially over the entire length of the dryer section, the drying occurs such that the side of the bottom surface of the web dries first and, when the drying makes progress, the drying effect is also extended to the side of the top surface of the web. Under these circumstances, the dried paper usually curls and becomes concave, seen from above.
With respect to the prior art related to the invention, reference is made to FI Patent 102623 which discloses a method in a paper machine or equivalent, wherein water is removed from a web or equivalent in a press and, after pressing, the web is dried in at least one dryer group based on impingement drying or equivalent. In this prior art arrangement, the web is guided along a substantially linear path or by using a large radius of curvature and, in the drying stage, after the impingement drying, the web or equivalent is dried in at least one dryer group in which a normal single-wire draw is applied, and the web is passed from the pressing stage to the drying stage as a closed draw and such that the web is constantly supported against at least one support surface. The above-mentioned patent discloses different types of applications for arranging impingement drying units in a dryer section, and with respect to arrangements of this type, reference is also made to the magazine article
Markus Oeschle: “Drying concepts for high demands
”, Paper ja Puu, Vol. 81,
No.
8/1999.
SUMMARY OF THE INVENTION
An object of the invention is to provide a dryer section and a dryer group in which the above-noted drawbacks and problems known in the prior art have been eliminated or at least minimized.
In addition, one object of the invention is to provide a dryer section concept that makes it possible to apply shorter and lower dryer sections than heretofore as compared with prior art dryer sections.
A further object of the present invention is to provide a dryer section which allows good runnability and a mainly closed draw of the web to be provided.
A further object of the invention is to enable a dryer section concept to be applied in which good quality of paper and sufficiently undisturbed runnability are achieved.
A further object of the invention is to provide a drying method and a dryer section applying the method in which the web reliably adheres to a drying wire over the entire length of the dryer section such that its cross direction shrinkage can be mainly inhibited, thereby avoiding cross direction inhomogeneities of the web caused by non-uniform cross direction shrinkage profile.
A still further object of the invention is to provide a dryer group and a dryer section having a new type of frame structure enabling compact dryer groups and a compact dryer section to be formed.
A still further object of the invention is to create a dryer group in which a factory-preseamed drying wire loop is threaded in place in the cross direction of the machine.
Thus, an object of the present invention is to offer new solutions to the problems discussed above so that said drawbacks as well as those coming out later in the prior art are chiefly avoided.
In accordance with the invention, the dryer groups of a dryer section are formed of at least one impingement drying unit, by means of which the web is dried directly, i.e. drying blowings are directed directly, not thr
Lathrop & Clark LLP
Metso Paper Inc.
Wilson Pamela
LandOfFree
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