US3452446A - Apparatus for the ventilation of a paper machine - Google Patents

Description

APPARATUS FOR THE VENTILATION OF A PAPER MACHINE Filed June 5, 1967 N E R G w L B L Sheet INVENTORSZ LARS BLOMGREN AKE JOHANSSON MW ATTYS.

y 1969 L. BLOMGREN ETAL 3,452,44

APPARATUS FOR THE VENTILATION OF A PAPER MACHINE Filed June 5, 1967 Sheet Arrys.

United States Patent US. Cl. 34-114 2 Claims ABSTRACT OF THE DISCLOSURE Apparatus for ventilating the casing of a dryer section of a paper machine wherein ventilating ducts extend horizontally along the length of the casing and are provided with a series of equally-spaced openings having adjustable dampers to adjust the distribution of the ventilating air exhausted therethrough along the length of the casing. The ducts on opposite sides of the casing are interconnected by a transverse passage which, in turn, is connected to an exhaust fan through an adjustable changeover damper which adjusts the relative amounts of air exhausted from the two sides of the casing.

The present invention relates to an apparatus for the ventilation of a paper machine, comprising a casing for the dryer section of the paper machine, which casing includes a roof, side walls and end walls, means for the supply of ventilation air to the casing and means for the removal of ventilation air from the casing.

It is known in the drying of paper by cylinder drying machines to provide the dryer section of the paper machine with a casing and to supply to as well as to remove from the casing controlled amounts of ventilation air. The casing ofiers the advantage that the temperature and moisture in the machine-room surrounding the paper machine can be maintained lower than without a casing, which renders the working conditions for the staff comfortable, and that the air temperature and air humidity in the dryer section of the paper machine can be maintained higher than without a casing, which results in an improved heat economy.

It is also generally known that it is difiicult to dry the paper web uniformly across its width in spite of the easing of the dryer section of the paper machine. As a rule, the drying result is worse in the middle of the web than at its edges, but a very usual phenomenon is also an uneven drying profile, at which the drying of one edge is worth than that of the other edge. In most cases an uneven drying profile is due to the fact that air flows across the paper web between the drying cylinders, whereby the paper web edge, at which the air flows in, is dried more than the edge, at which the air leaves the web.

In the common types of casings the ventilation air is supplied through the basement floor below the dryer section or immediately below the usual lower drying felts, and removed through a gap or openings along the longitudinal central line of the roof. This is a natural method in view of the decreasing density of the air on its passage through the dryer section, which partly is due to its mixing with evaporated water vapour and partly to its heating by contact with the heated drying cylinders. In this way, the possibilities of self-draught are utilized.

A cylinder dryer section, however, is never symmetric with respect to the central portion of the paper web, because on one side thereof there are arranged the transmissions for the operation of the drying cylinders and the steam fittings for the heating of the cylinders. Said fittings comprise a great number of hot pipes, which produce thermal forces tending to press up great amounts of air on this side. Under these conditions an air flow across the machine easily can develop. The vertical flow areas on both sides of the machine can have different size, which also contributes to the development of a cross flow.

By the invention a ventilation apparatus has been achieved, by which the cross-flow tendencies and, thereby, the uneven drying profile can be controlled. Said apparatus is characterized in that the means for the removal of ventilation air from the casing comprise exhaust passages extending horizontally along each of the side walls adjacent the roof, which passages communicate both with the dryer section via openings in the passage walls and with gas transport means associated with the last-mentioned means, said means for the removal of drying air being arranged such that the amount of ventilation air removed per time unit from the casing via the exhaust passages can be adjusted individually for every passage.

Other characterizing features of the invention are evident from the following description and the accompanying drawing, in which:

FIG. 1 is a cross sectional view through a dryer section in a paper machine having ventilation apparatus made in accordance with the present invention; and

FIG. 2 is a diagrammatic sectional view taken on the line 2-2 of FIG. 1.

The drying section comprises a machine stand 1 and a number of drying cylinders 2, about which the paper web is directed in a zigzag path. The machine stand is supported on so-called supporting strands 3 of concrete. Above the machine stand 1 a light-weight frame 4 is mounted carrying the upper portion of the casing. The right-hand portion of the machine stand 1 includes the transmission for the operation of the drying cylinders. To the right of the transmission the steam and condenser tubes 5 for the heating of the drying cylinders are located.

The casing comprises of a roof 6, a side wall 7 on the machine operators side, a side wall 8 on the driving side of the machine and two end walls (not shown). For making the dryer section accessible for operation, a number of liftable doors 9 and a number of slidable doors 10 are provided in the side wall 7 on the operators side and a number of slidable doors 11 are provided in the side wall 8 on the driving side.

It is not possible for a reasonable price to make the doors in the casing fully tight. Certain areas of leakage must, therefore, be accepted. Furthermore, the casing must be provided with holes for a great number of pipes and cables. The leakage areas, therefore, can have a relatively great size. In order to avoid the outflow of hot moist air from the casing through the leakage areas into the machine room one tries to maintain some vacuum within the casing, and it is calculated that 30% of the air amount exhausted from the casing is supplied as leakage through unavoidable openings.

For removing by ventilation the Water vapour which evaporates from the drying paper web the casing is supplied with heated ventilation air through a passage 12 which extends along the central line of the machine in the basement floor below the dryer section. The upper wall of the passage, along the length of the dryer section, is provided with a number of slots 13 for distributing the ventilation air supplied through the passage. For the removal of the ventilation air, according to the invention, two exhaust passages 14 and 15 are arranged to extend horizontally below the roof 6 adjacent to each of the side walls 7 and 8 along the entire length of the dryer section. The exhaust passages 14, 15 communicate with the dryer section via openings 16, 17 in the passage walls and with the suction side of a number of exhaust fans 3 18 via ducts 19, 20, 21. The openings 16 17 in the passage walls are uniformly distributed along the length of the dryer section and provided with sliding dampers 22, 23 for controlling and adjusting the distribution of the exhausted ventilation air in accordance with the drying intensity in the different parts of the dryer section.

As mentioned above, the air flows often across the dryer section in horizontal direction and thereby imparts to the finished paper web an uneven dry-content profile. One reason which strongly contributes to said profile is the thermally caused air motion about the steam fittings on the drive side of the machine. Further contributions can be effected by the aforementioned leakage areas, The exhaust on two sides according to the invention renders it possible to eliminate the cross flows. It is, for example, possible to counteract and neutralize an air flow flowing horizontally between the drying cylinders past the paper web from the drive side to the operators side by increasing the air amount removed through the exhaust passage of the drive side from the casing or, more correctly, by changing the relation between the air amounts removed through the two exhaust passages. This change is eifected by a continuously adjustable change-over valve 24 located in the meeting point between the ducts 19, 20 from the exhaust passages 14, 15. Such a valve 24 is provided for each of the fans 18. The arrangement offers simple but effective possibilities of controlling the air flow in the casing to the degree required.

We claim:

1. An apparatus for ventilation of a paper machine, comprising a housing completely enclosing the cylinder dryer section of the paper machine, which housing includes a roof, side walls and end walls, means for the supply of ventilation air to the housing including an air distribution channel disposed below the drying cylinders and extending along the entire dryer section, and means for the exhaustion of the ventilation air, the improvements wherein the means for the exhaustion of the ventilation air comprises two separate exhaust ducts extending horizontally along each of the side walls of the housing adjacent the roof of same, said exhaust ducts communicating with the dryer section through a number of openings uniformly interspaced along the length of the dryer section, each opening being provided with an individually adjustable damper, at least one exhaustion fan at least one transverse passage interconnecting both of the two exhaust ducts to the exhaustion fan, and an adjustable change-over damper in said passage whereby the amount of exhausted ventilation air can be individually adjusted for each exhaust duct, and the distribution of the exhausted ventilating air is adjustable along the length of the dryer section.

2. An apparatus according to claim 1, wherein there are a number of separate exhaustion fans, each of the two exhaust ducts being connected to said separate exhaustion fans.

References Cited UNITED STATES PATENTS 2,000,546 5/1935 Woodsome 34-114 XR 2,909,847 10/1959 Hornbostel et al. 34-114 XR 2,910,784 11/1959 Metcalfe 34-114 2,977,686 4/1961 Stout 34-114 CARLTON R. CROYLE, Primary Examiner.

ALLAN D. HERRMANN, Assistant Examiner.

US. Cl. X.R. 34-235

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