Drying and gas or vapor contact with solids – Apparatus – Rotary drums or receptacles
Reexamination Certificate
1998-10-08
2001-02-13
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Apparatus
Rotary drums or receptacles
C034S124000, C034S624000, C034S636000
Reexamination Certificate
active
06185836
ABSTRACT:
DESCRIPTION
Rollers or rolls as used in paper making machines are often heated due to the various technical requirements. This usually is done by a medium serving as the heat carrier being sent through cavities in the roller, as a result of which heat is transferred to the shell of the roller, heating it up. In this arrangement both a central cavity may be provided in the roller as well as annular cavities arranged between a displacement body located in the center of the roller and its surrounding roller shell. However, just as well, passages may be arranged near to the periphery of the roller shell oriented axially parallel, evenly spaced radially from the center of the roller and thereabout. The heat carrier medium generally used is a liquid such as water or oils. It is especially in the case of the so-called smoothing station at the end of the paper making machine, in which the surface of the paper is upgraded by heated smoothing, that supplying heat to the roller requires particular care. This is why considerable efforts are made in design to achieve a consistently high heat transfer to the surface or shell of the roller over its full length.
Recently it has been recognized that it may make sense to use steam as the heat carrier medium. The advantage afforded by this choice is that considerably less quantities of the heat carrier medium are needed, thus making major savings in energy possible which result in likewise considerable cost savings in the process as a whole. In addition to this, process steam is mostly adequately available in any case in paper making. Such steam-heated rollers are described in the German patent applications DE 43 13 379 A1 and DE 44 07 239 A1 in which the steam is guided through peripheral passages in the roller shell where it condenses, giving off its thermal energy to the roller shell. Collecting spaces are provided at the corresponding ends of the passages from which the resulting condensate or condensate/steam mix may be syphoned off from the roller by syphon means.
One drawback in heating rollers with steam is that such rollers cannot be cooled. If the machine is halted for changing the roller or due to remedial action being needed in the systems connecting the roller, a wait has hitherto been necessary to allow the roller to cool down by convection and irradiation of the thermal energy to a temperature suitable for roller handling. This takes up a lot of time in view of the rollers concerned weighing anything up to a 100 tonnes and having operating temperatures of up to 200° C. which can hardly be tolerated as downtime for paper making machines which are usually operated non-stop. This is why a broad application of steam-heated rollers has failed to find acceptance.
Cooling heated rollers, or rollers having otherwise an increase in temperature, e.g. due to friction in operation has been recognized as a task for which technical solutions have been sought. Accordingly, e.g. DT 24 00 615 A1 discloses a hollow roller filled at least in part with a heat carrier medium, in the interior of which a heat exchanger is provided connected to a means of increasing or decreasing the temperature outside of the roller so that the heat carrier medium in coming into contact therewith may be heated or cooled. However, designs of this kind, irrespective of their other disadvantages, fail to qualify for cooling a steam-heated roller because the suitable heat carrier medium is lacking. On cooling, steam would simply condensate, the condensate failing to fill the interior of the roller completely.
The object of the invention is to specifically cool steam rollers and to shorten the time needed for cooling. It has been discovered that this shortening is achievable to a surprising extent, for instance, from 15 hours to 150 minutes in the case of a pertinent 70 ton roller. The invention simultaneously opens up the possibility of operating steam-heated rollers also at a temperature level which is below the steam temperature should this prove desirable or necessary for specifically reasons without having to switch the heating system over to another heat carrier. Steering the temperature of the roller in this way is also lastingly possible with a suitable roller design by steam being guided through the roller body at higher operating temperatures, and at lower temperatures, condensate, i.e. water, the temperature of which is regulated outside of the roller.
The invention will now be described with reference to
FIGS. 1
to
7
b
of the drawings.
REFERENCES:
patent: 4955433 (1990-09-01), Zaoralek
patent: 5285844 (1994-02-01), Schneid
patent: 5662572 (1997-09-01), Zaoralek
patent: 5967958 (1999-10-01), Borkenhagen et al.
patent: 2139114 (1994-11-01), None
patent: 1361096 (1974-07-01), None
Ratner & Prestia
Schwabische Huttenwerke GmbH
Wilson Pamela
LandOfFree
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