Drying and gas or vapor contact with solids – Apparatus – Rotary drums or receptacles
Patent
1985-06-24
1986-12-09
Schwartz, Larry I.
Drying and gas or vapor contact with solids
Apparatus
Rotary drums or receptacles
34119, 34124, 165 90, 219244, 219470, F26B 1318
Patent
active
046271767
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention concerns papermaking machines, and refers in particular to a drying cylinder designed for equipping a drier and/or after-drier section for machines producing paper, cardboard or any other material in webs.
PRIOR ART
In papermaking machines, the paper web is already well formed when leaving the press section, the main problem then is to bring the percentage of water in the web, which ranges from 60 to 65% approximately, down to a value lying between 5 and 10%. This is performed in a drier section in which the wet paper web coming out of the last press and containing 60 to 65% of water, is put in close contact with a number of large drying cylinders whose diameter is generally 1.5 m, and which are internally stem heated, the wet paper web being strongly pressed against the outer surface of the cylinders by means of felt. The drying cylinders or drums are set up in two rows, a top and a bottom row, and are generally grouped in trains of three to twenty cylinders, each train being associated with its own felt which unrolls towards the bottom or the top, while each felt is dried by a felt drying cylinder or drum. The paper web successively moves from a lower drying cylinder to an upper drying cylinder, and vice versa. Suitably placed blowers remove the thin steam saturated air film which tends to continuously form and stagnate on the wet paper web, and the steam released is gathered by a hood and exhausted. In these driers with internally steam heated drying cylinders, 1.3 to 1.5 kg of steam are required, depending on the installations and the type of pulp, to evaporate one litre of water contained in the wet paper web.
In drier sections developed more recently, the felt has been suppressed and each drying cylinder has been surrounded by an individual hood with numerous openings, in the form of holes and slots, communicating with a hot air blowing installation and a steam exhausting installation.
These two types of driers have a common disadvantage, their operating cycle presents an important inertia and the control for the operation of the heavy and complex mechanical and thermal assemblies which constitute these driers, poses numerous problems. For this reason, a large number of devices have been designed and are used for controlling the quantity and the quality of the steam taken in by the drying cylinders at the different stages of the paper web evaporation in the drier. In practice, the major difficulty to be overcome consists in maintaining an even degree of dryness over the whole width of the web or also in keeping the required moisture configuration. For this reason, the modern papermaking machines comprise various devices which permit, by means of an additional hot air flow, local dehydration of the web parts which are too wet, or by spraying water, wetting of the web parts which have become too dry.
The various disadvantages mentioned above are also common in the papermaking machines in which the drier cylinders have been partly or completely replaced by a enormous single cylinder known as the machine glared cylinder whose diameter can range from 3 to 6 m, and which is surrounded by a high-efficiency hood.
In some papermaking machines, the drier is followed by a size press. In this case, the latter is itself followed by an after-drier section, which is in fact a second drier section smaller in number of cylinders than the main drier, and it is obvious that these papermaking machines also have, as far as the drier unit is concerned, the same diadvantages as the state of the art installations mentioned above.
After going over one or two cooling cylinders, which are fitted at the drier or after-drier end, the paper web can be considered as being fully formed and can then be wound on the main rolls. But, in most cases, the paper webs, before being wound on the main rolls, are treated in order to improve their surface condition and/or their internal structure. When these treatments are carried out on the papermaking machine itself, the paper web coming from the drier or a
REFERENCES:
patent: 3203678 (1965-08-01), Sawyer et al.
patent: 3624353 (1971-11-01), Bjorklund
patent: 3805020 (1974-04-01), Bates
patent: 4440214 (1984-04-01), Wedel
patent: 4535230 (1985-08-01), Brieu
Breiner A. W.
Chleq Frote et Cie
Schwartz Larry I.
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