FI72775B - FOERFARANDE OCH ANORDNING FOER ATT FOERBAETTRA EN TORRBANDSPROCESS. - Google Patents

Abstract

A method and device for improving a web-drying process, in which air containing particles is sucked into a suction compartment (5) from the interior of a former (2) or the like through the web of material (3) being formed and through a movable screen (4). The method is improved due to the fact that the air containing particles sucked into the suction compartment (5) is blown back through a channel system (7) into the upper part of the same or another former (2, 12) and, from there, it is sucked into a suction compartment (5, 13) below the respective former (2, 12). <IMAGE>

Description

72775

METHOD AND APPARATUS FOR IMPROVING THE DRY LENDING PROCESS - FÖRFARANDE OCH ANORDNING FÖR ATT FÖRBÄTTRA EN TORR-BANDSPROCESS

The present invention relates to a method and apparatus for improving a dry web process in which particulate air is sucked into a suction box through a former or similar web of material and a moving wire.

In current dry printing machines, the recycling of suction air into suction air has not been used, mainly due to many technical problems. Recirculation of air in the dry drawing process generates static electricity which has a detrimental effect throughout the process, e.g. during the web formation step, loose fibers or other particles adhere to each other under the action of static electricity, forming bundles which adversely affect the quality of the web to be formed. In addition, static electricity can create an explosion hazard if the mixture of air and particles is in an explosive atmosphere.

On the other hand, recirculation of air streams is not always economically viable, especially if the filtration of the air streams blown into the outside air does not have to be done and if the dry paper mill is built in areas with such a warm climate that no replacement air needs to be treated, e.g. However, when building dry paper mills in cold-climate areas, significant economic savings can be achieved by recycling intake air.

Another problem has been the adverse effect of air circulation on the cross-sectional profile of the track to be formed. If the forming part is completely open at the top and the intake air is taken from the surrounding hall, this problem naturally does not exist. In this case, the intake air is taken from the hall through the former wire to the suction box.

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The recovery of fibers and other particles passing through the wire in current dry web machines is difficult and expensive. Even if the particles are recovered from the intake air, their reuse can become a problem.

On the other hand, the disadvantage of current dry paper machines is the difficulty in controlling the humidity of the intake air. If the hall air is too dry, the entire ambient air must be humidified simply because the intake air of the forming part must not be too dry due to the generation of static electricity.

Various dryers have traditionally recycled hot air. In this case, however, the reason for removing air from the air circulation is the need to remove the moisture evaporated in the dryers together with the exhaust air.

In some cases, such as in the apparatus of U.S. Patent 3,906,588, the dry forming process itself requires the recirculation of the transport air of the fibers f V in the web forming section.

It is an object of the present invention, first, to provide for the recovery of particles passing through a wire. One purpose is to reduce the size of air handling equipment used in the dry-drawing process, such as filtration, cleaning, humidification and heating equipment, and thus achieve cost savings in investment and operating costs. Yet another object of the present invention is to reduce the need for heating of the replacement air introduced into the process and to achieve better control of the static electricity and humidity of the intake air.

The method according to the invention is thus characterized in that the particulate air sucked into the suction box is blown along the duct back to the upper part of the same or another 72775 former, from which the air is sucked into the suction box below the former.

A preferred embodiment of the method according to the invention is characterized in that a part of the particulate air is removed through the duct before blowing through the material path.

Another preferred embodiment of the invention is characterized in that the static electricity generated in the air circulation is eliminated by humidifying the circulating air.

The apparatus in which the method according to the invention is applied is characterized in that at least one mold is provided with an apparatus for circulating particulate air sucked from the former through the web and back to the top of the same or another former to be re-sucked through the web and wire. to the suction box below the former.

A preferred embodiment of the apparatus according to the invention is characterized in that the apparatus comprises a duct through which at least part of the recirculated air can be removed.

In the following, the invention will be explained in detail by means of exemplary embodiments with reference to the accompanying drawings, in which

Fig. 1 shows the forming part of a dry paper machine obliquely when viewed from the side.

Fig. 2 shows a flow diagram of the forming part according to Fig. 1 with three formers.

Fig. 3 shows a flow chart of an embodiment in which air is blown from a suction box to the top of an adjacent former.

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Figure 1 shows a dry paper machine forming part comprising two formers 1 and 2, which are described in more detail in, for example, U.S. Pat. No. 4,352,649. Former 1 does not have a suction air return circuit, while former 2 has suction air recirculation. Air is sucked in through the material path 3 to be formed from inside the former 2 and the moving wire 4 to the suction box 5 by means of a fan 6. From the fan 6, air is blown along the duct 7 back to the upper part of the former 2, from where it is again sucked into the suction box 5. The smallest possible part of the circulating air is further removed through the duct 8, for example to a filter. In turn, the same amount of air is introduced into the air circulation, mainly as- ... transport of air by air and leakage air. If necessary ; the circulating air is humidified with, for example, steam by means of steam nozzles 9.

Fig. 2 shows a flow diagram of a forming part according to Fig. 1 with three formers 2. In the former: a mixture of particles and air is sucked by means of a blower 6 through the wire 4 and the material path formed thereon into the suction box 5. The air and wire passing from the suction box the mixture of particles is blown into the same former. Part of the intake air is removed from the air circuit and the amount of exhaust air can be adjusted, for example, with control dampers 11. The amount of air corresponding to the exhaust air ** / "enters the recirculated air, for example as air transport and leakage air.

In Fig. 3, the air recirculation is implemented in such a way that the mixture of particles and air in the former 2 is sucked by a fan 6 through the wire 4 and the material path formed thereon into a suction box 5, from where the particulate air is blown into another former 12. through the web of material and the wire to the suction box 13 of the same former 12. Also in this case, the amount is adjusted, for example, by means of control dampers 11.

It will be clear to a person skilled in the art that the invention is not limited to the above-mentioned exemplary embodiments, but can be modified within the scope of the appended claims. Thus, the former may also be of a different type than the drum former shown in the figure.

Claims (6)

6,72775 A method for improving a dry-drawing process, in which particulate air is sucked into the suction box (5) through a former (2) or similar internally formed material web (3) and moving wire (4), characterized in that particulate air sucked into the suction box (5) is blown ) back to the top of the same or another former (2, 12) from which air is sucked into a suction box (5, 13) below that former. Method according to Claim 1, characterized in that part of the air sucked from the suction box (5) is removed via the duct (8) before it is blown back to the upper part of the former (2, 12). Method according to Claim 1 or 2, characterized in that the static electricity generated in the air circulation is eliminated by humidifying the circulating air. Method according to one of Claims 1 to 3, characterized in that the rise in the temperature of the circulating air is limited by means of cooling devices or by adjusting the volume flow of the air removed from the air circulation by means of control dampers (11). An apparatus according to claim 1, wherein the apparatus comprises one or more formers (1, 2, 12) or the like located above the web (3) to be formed on the moving wire (4), and one or more molds located below the wire. suction box (5, 13), characterized in that at least one former (2, 12) is provided with an apparatus for circulating particulate air sucked from the former through the material web (3) and the wire (4) along the duct (7) back to the same or to the top of another former to be re-sucked through the web of material and wire into a suction box (5, 13) below that mold. 72775 Apparatus according to claim 5, characterized in that the apparatus comprises a duct (8) from which part of the air sucked from the suction box (5) is removed before blowing into the upper part of the former (2, 12). 8,72775