Drying and gas or vapor contact with solids – Process – Diverse types of drying operations
Reexamination Certificate
2000-02-01
2001-09-25
Gravini, Stephen (Department: 3749)
Drying and gas or vapor contact with solids
Process
Diverse types of drying operations
C034S445000, C034S448000, C034S461000, C034S631000, C034S633000, C034S638000, C034S640000, C034S643000
Reexamination Certificate
active
06293031
ABSTRACT:
The present invention relates to a method and an apparatus for drying a coated paper web or the like.
From the U.S. Pat. Nos. 5,771,602 and 5,230,165, it has previously been known to turn a coated but still undried paper web or the like in a non-contacting way by blows generated by a turning device before the web is actually dried in a non-contacting way by airborne web-dryers arranged on both sides of the web.
From the U.S. Pat. No. 5,230,165, it is also per se known to arrange curved counterpart provided with underpressure nozzles against the turning device on the other side of the paper web. The purpose is to begin the drying of the paper web on both sides of the web already at the curved section of the web. The underpressure nozzles have a relatively limited drying capacity, as drying air is blown to flow principally in the direction of the web along the nozzle surface, utilizing the Coanda effect. In the arrangements shown, the moist and still warm drying air blown from the underpressure nozzles is allowed to flow from the counterpart directly into the machine room surrounding the apparatus, which adversely increases moisture and heat in the machine room, in addition to the fact that wasting heat as such does not conform to principles of sound energy economy.
Due to the Coanda effect, a static underpressure zone is formed between the nozzles and the web in the nozzle area in the counterparts known per se, principally over the entire nozzle area. The aim is to use this underpressure to intensify the pushing effect of the turning device by means of suction in the counterpart area. Suction is used to spread the web outwards in order to stabilize the web on its curved course. However, regarding these arrangements provided with underpressure nozzles, there is a risk that the paper web, should it lacken for example due to tension variations, contacts the nozzles of the counterpart whereupon the coating is damaged and/or the web breaks.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide a new, improved method and an apparatus in which the drawbacks presented above have been minimized.
It especially is an object of the present invention to provide a method and an apparatus with which it is possible to achieve an improved runnability or controllability of a paper web or the like.
It is further an object of the invention to provide a method and an apparatus which make it possible to lead the paper web or the like more safely through a slot formed by the turning device and the counterpart.
A further object is to provide a method and an apparatus providing a larger drying capacity of the paper web than before, and thus save space in the machine room.
It is a further object to provide a method and an apparatus with which it is possible to decrease the moisture and thermal load in the machine room and thus simultaneously improve the energy economy of the process.
The in which the running direction of the paper web (W) to be dried is turned in a non-contacting way by using blows generated by blow nozzles of the turning device and by pad pressure thus generated;
The paper web is dried in a non-contacting way with drying devices.
The apparatus typically comprises a counterpart provided with overpressure nozzles, the counterpart being arranged at the curved turning device area on the opposite side of the paper web.
Overpressure nozzles refer here to nozzles the blows of which generate a web pushing power at all distances from the web. In the known arrangements described above, the starting point has been the reverse; in them, underpressure nozzles have been used for generating at a certain distance from the web a power opposite to the pushing power in order to spread the web. With the overpressure nozzles of the invention, it is possible to control the running of the web better and to ensure that the web stays apart from the nozzles.
In an advantageous arrangement of the invention, the counter-part may be provided with, for example, Float or Push nozzles disclosed in the applicant's U.S. Pat. No. 4,384,666. On the other hand, if desired, the counterpart may also be provided with simple impingment nozzles which include, for example, a perforated plate or one or more slots extending across the web, from which air is blown principally directly against the web.
The overpressure nozzles of the counterpart are advantageously arranged radially against the blow nozzles of the turning device, i.e. so that blows from the counterpart are directed against the paper web and against the blows from the turning device arranged on the first side of the web. Thus the blows, for example from Float overpressure nozzles, generate a local overpressure on both sides of the web between the paper web and the carrier surfaces of the nozzle, i.e. the nozzle surfaces; with this overpressure, the running of the paper web may be stabilized and the runnability and controllability of the web may be improved. Impingment nozzles provide the same result, although the pressure generated by the impingment nozzles generally is slightly lower than the pressure generated by overpressure nozzles of the Float type.
On the straight run of the paper web arranged after the turning section, i.e. in the drying section, floating nozzles on the opposite sides of the paper web are, however, arranged advantageously interlaced with each other so that the web travels in a sine-wave path between the nozzles arranged on both sides of the web, which allows an as smooth as possible web run. It is naturally possible that also part of the nozzles in the turning section of the web are arranged interlaced with each other.
In the turning section of the device, the running direction of the web may be turned even 20°-260°, typically 30°-160°.
The actual turning device of the invention, in which the running direction of the paper web may be turned 20°-260°, comprises typically 3-15 blow nozzles. The counterpart advantageously comprises the same number of overpressure nozzles, i.e. 3-15 nozzles. Also the blow nozzles of the actual turning device are preferably overpressure nozzles.
According to the invention, the pushing nozzles of both the turning device and the counterpart are principally so-called Float overpressure nozzles of the applicant. As the nozzles in the turning section additionally are arranged opposite to each other on both sides of the web, the pushing forces caused by the nozzle flows are directed against each other. This generates a local overpressure at the carrier surface areas of the nozzles on both sides of the web. The local overpressures arranged opposite to each other on both sides of the web have a stabilizing effect on the web run, and improve the runnability and controllability of the web, also in cases of disturbance. Thus the arrangement of the invention provides an optimal configuration of nozzles as to the control of the web.
With the arrangement of the invention, in which overpressure nozzles, such as Float nozzles, are used in the counterpart instead of underpressure nozzles known per se, such as Foil or Pull nozzles disclosed in the applicant's patent U.S. Pat. No. 4,247,993, for example the important advantage is achieved compared with the known technology, that it is considerably less probable that, due to tension variations, the paper web would contact the nozzles of the counterpart or the turning device, because the overpressure nozzle pushes the web away, while an underpressure nozzle is not necessarily always able to keep the web away from the nozzle surface.
The turning device of the invention is further advantageously provided with a control device, increasing the controllability of the turning device and making it possible to automatically control the distance between the turning device and the web, this control being based on the ratio between the supply air pressure of the turning device and the pad pressure. In addition, the pressures may be used for automatically calculating the tension of the web.
Thereby the control device typically comprises
a pressure sensor arrang
Ringbom Knut
Solin Richard
Gravini Stephen
Metso Paper Inc.
Nixon & Vanderhye P.C.
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