Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
1999-02-23
2001-10-16
Silverman, Stanley S. (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S308000, C162S318000, C162S357000, C034S116000, C034S114000, C034S115000
Reexamination Certificate
active
06303003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to paper making and, more particularly, pertains to a new method and apparatus suitable for drying a paper web.
2. Description of the Prior Art
Current industrial practice is to manufacture paper by successively forming pressing and drying a moist fibrous web. This process is characterized by a relatively high energy consumption which accounts for much of the capital and operating cost in papermaking.
One problem resides in the fact that known suction rolls shed vacuum at each turn. For a sheet as porous as newsprint, for example, the air volume shed from drill holes defined in the peripheral surface of the suction roll is about equal to the air drawn through sheet pores. Therefore, half the vacuum pump energy is lost.
A second problem is a discharge of the vacuum pumped, to the atmosphere, thereby wasting the heat of vapor compression.
A third problem is that known suction roll have a centrifugal throw of moisture toward the sheet, at the sheet exit from the roll, undoing some drying just done.
A fourth problem is moisture removal by intermittent forces, including foil pulses, suction and press pulses, heat pulses, each force followed by a lapse of drying force, i.e. ineffective travel. Moreover, surface tension and capillary action let moisture migrate backward, a type of rewetting which undoes drying just done.
A fifth problem occurs during sheet transfers, disturbing fiber bonds and sheet dimensions because the sheet is damp and weak.
A sixth problem is a need to synchronize speeds between machine sections requiring controls which are costly to buy and maintain.
Another problem is the loss of drying heat to the atmosphere thereby wasting fuel and investment in a steam plant.
SUMMARY OF THE INVENTION
It is therefore an aim of the present invention to provide an improved drying process and apparatus which reduces the energy required to make paper.
Therefore, in accordance with the present invention there is provided a method comprising the steps of: delivering a continuous web of fibrous, moist material to a porous conveying surface; drying the web by continuously drawing superheated vapor through the web as the paper is being formed and pressed; and removing the web as dried paper from the porous conveying surface.
In accordance with a further general aspect of the present invention, there is provided a process for drying a moist web of paper in a papermaking machine of the type having a porous flexible endless conveying member in driving engagement with a porous peripheral surface of a hollow cylinder mounted for rotation about a main axis thereof, comprising the steps of applying a vacuum outside a portion of the porous peripheral surface of the hollow cylinder which is free from engagement with the porous flexible endless conveying member so as to cause a flow of moisture from the web, through the porous flexible endless conveying member and the porous peripheral surface, to a source of vacuum, compressing a vapor portion of the moisture drawn from the web such as to form a mixture of condensate and saturated vapor, expanding the saturated vapor to form superheated vapor, and recirculating the superheated vapor in a substantially closed air impervious system to be used again in the drying of web.
An apparatus for making paper in accordance with the present invention comprises a porous endless conveying member in drive engagement with a porous peripheral surface of a hollow cylinder mounted for rotation about a main axis thereof, and a drying medium circulating system for uninterruptedly drawing moisture from the web. The drying medium circulating system comprises a vacuum hooded section disposed for collecting the moisture at a portion of the porous peripheral surface of the hollow cylinder which is free from engagement with the porous endless conveying member.
According to a more specific construction of the present invention, pressing means are provided for compressing the web against the porous peripheral surface of the hollow cylinder as the web is conveyed thereover by the porous endless conveying member.
REFERENCES:
patent: Re. 28459 (1975-07-01), Cole et al.
patent: 1767889 (1930-06-01), Jurgensen
patent: 2091805 (1937-08-01), Chuse
patent: 2718710 (1955-09-01), Spooner
patent: 2896336 (1959-07-01), Shoumatoff
patent: 4247990 (1981-02-01), Ohls et al.
patent: 237426 (1924-01-01), None
patent: 270607 (1927-05-01), None
Article from the Pulp and Paper Magazine of Canada, Nov.1/68, pp. 55 & 56—“The Papridryer—1. The Basic Concept and Pilot Plant Results”—Burgess, B.W. et al.
Article from the Pulp and Paper Magazine of Canada, Jun. 1961, pp. T-303-309—“The Drying of Web Materials”—Burgess, B.W.
Diller, Ramik & Wig
Silverman Stanley S.
Walls Dionne A.
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