Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Patent
1997-10-10
2000-10-10
Wilson, Pamela A.
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
34402, 162206, F26B 300
Patent
active
061288330
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a dryer-section concept and a method in the drying of a paper/board web.
The invention concerns a dryer section of a novel type for a paper machine, by means of which dryer section it is possible to enhance the drying and to improve the control of curling without deterioration of the runnability of the dryer section and of the efficiency of the paper machine.
BACKGROUND OF THE INVENTION
In the prior-art dryer-section concepts based on single-wire draw, in view of prevention of curling of paper, it is necessary to invert at least one group, in which case the paper is also dried from the other side. It has been noticed that, in the event of a web break, such so-called inverted groups with single-wire draw are difficult to clean, and the fibre strings produced may break wires and blow boxes and produce unnecessary losses in production.
The system of the present sort can be abandoned by using a drying geometry in which the dryer section consists of drying cylinders and of impingement units fitted on said cylinders, out of which impingement units hot air/steam is blown through the wire onto the paper. By means of such an impingement unit, a considerable increase in the evaporation capacity is achieved. In such a case, the evaporation takes place increasingly from the wire side on the cylinder. Owing to the increased evaporation capacity, the dryer section can be made shorter, thus obtaining economies in the cost of construction of the hall. Owing to the increased evaporation capacity, the concept of the invention can also be applied to modernizations, in which the available space is often quite limited.
From the application JP 222,691/1993, a dryer section is known in which there is an impingement hood placed on the top of all of the upper cylinders. In the present invention of ours, the impingement hoods are preferably placed in connection with the cylinders only at which the hoods provide a considerable effect either on the control of curling or on an increased drying capacity.
When the impingement is carried out through the wire, the paper is protected between the wire and the cylinder and it has no possibility to form so-called agglomerations, which might collide with the impingement device itself and damage it.
An increase in the evaporation on the cylinder normally results in a lower average temperature of the web and thereby slightly reduces the evaporation taking place in the area of free draw, but, on the other hand, the delivery of heat by the cylinder is increased, which increases the overall evaporation.
The impingement unit can also be divided into blocks in the direction of width of the machine, in which case, by means of the unit, it is possible to act upon the evenness of the moisture profile in an attempt to improve the uniformity of the final product in the cross direction of the web.
SUMMARY OF THE INVENTION
The dryer-section concept in accordance with the invention is mainly characterized in that the dryer section comprises a plurality of drying cylinder groups including one or more single wire draw drying groups having suction cylinders, heated drying cylinders, a drying wire on which a web is carried and guide means for guiding the drying wire while the web is carried thereon between the suction cylinders and drying cylinders. The drying wire is guided from one suction cylinder onto a drying cylinder, from that drying cylinder onto another suction cylinder and from this suction cylinder to another drying cylinder and such that the web is interposed between a face of each drying cylinders and the drying wire while the web runs over the drying cylinders and the drying wire is interposed between the web and the suction cylinders while the web runs over the suction cylinders. Impingement units are provided, each arranged in opposed relationship to a respective drying cylinder and including means for directing a heated medium through the drying wire at the web, since the web is interposed between the drying wire and the face of the drying cyl
REFERENCES:
patent: 3089252 (1963-05-01), Daane et al.
patent: 4183148 (1980-01-01), Koski et al.
patent: 5586397 (1996-12-01), Kerttula et al.
patent: 5862613 (1999-01-01), Kerttula et al.
Edelmann Kari
Juppi Kari
Karlsson Markku
Valmet Corporation
Wilson Pamela A.
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