HOOD FOR A WIRE PART AND FOR A PRESS SECTION

The invention concerns a hood for a wire part and/or for a press section in a paper/board machine, comprising walls and a ceiling, which form a closed hood around the wire part and/or the press section, air-conditioning being arranged in connection with the hood.

It is known from the prior art to place the wire part, the press section, and/or the dryer section of a paper machine inside a hood. The aim of said hood in respect of the wire part has been in particular to prevent spreading of drops into the machine hall. In the area of the press section, in view of energy economy, there has been an attempt to obtain economies as the pressing of the paper web is accomplished more efficiently, because the web and the felts that are used are warmer. It has been a further object of the hood to operate as a noise insulation and to separate the wire part and the press section from the rest of the machine hall, in which case the hood prevents spreading of moisture into the machine hall. In the dryer section, by means of a hood, attempts are made in particular to reduce the consumption of energy and to prevent spreading of heat, moisture and noise into the machine hall.

With respect to the prior art related to the dryer section, reference is made, for example, to the paper Wochenblatt für Papierfabrikation 23/24 1992, F. Sodec: Neues Haubenkonzept für energiesparende Papiertrocknung, in which paper an exemplifying embodiment is described of a concept in which, in the dryer section, a hood and an air-conditioning arrangement are employed.

With respect to the prior art related to the dryer section, reference is also made to the FI Patent 63,980, in which a method is suggested for enhancing the air-conditioning in dryer sections provided with a closed hood in paper machines. In this cited paper, particular emphasis is placed on arranging the air-conditioning of the hood so that problems arising from condensation can be prevented.

With respect to hood arrangements related to the press section of a paper machine, reference is made to the FI Patent 83,551, in which a press section of a paper machine is described, in particular a press section in which suction rolls are used. According to the cited paper, the press section is covered with a hood, whose construction is such that it both raises the temperature of operation of the press section and reduces the noise level in the environment outside the press section to a substantial extent. In the arrangement in accordance with said cited paper, the hood consists of displaceable wall and ceiling elements at the tending side and of displaceable or fixed wall elements at the driving side. Said elements of the hood have been made of a sound-insulating material, which is transparent at the tending side. What is described in said cited paper constitutes the prior art most closely related to the present invention, and one of the objects of the present invention is further development of the arrangement described in said cited paper while also applying said arrangement to the wire part and while, in particular, paying attention to problems related to the arrangements of supply of air as well as to the construction of the hood elements proper.

It is a further important component factor to arrange the hood so that it does not produce problems of cleaning.

It is a further object of the invention to develop the solution described in said cited paper so that, when necessary, the shifting of the wall constructions can be accomplished easily and simply.

It is a further object of the invention to prevent condensation in the start-up stage and in the initial stages of production.

It is a further object of the invention to provide an arrangement by whose means the hood in the area of the wire and in the area of the press can be sealed so that the area inside the hood and the area outside the hood, respectively, constitute air-conditioning units of their own.

In view of achieving the objectives stated above and those that will come out later, the arrangement in accordance with the invention is mainly characterized in that the hood walls are composed of outer and inner walls, so that between them there is an air duct for passing a replacement air flow into the interior of the hood towards a substantial middle area of the paper machine through openings that have been made into the inner wall, the replacement air keeping the interior of the hood substantially dry and clean.

According to the invention, the replacement air is supplied into the hood of the wire part and of the press section from the wall and ceiling elements, the elements being heatable while the air flows in the frame space in the space between the two walls of the wall element. The dry replacement air is discharged, for example, through slots all over the area of the wall and ceiling faces into the interior of the hood. Then, the walls and the ceiling remain clean and dry as the elements are warm, in which case there is no risk of condensation. In the arrangement in accordance with the invention, the necessary replacement air is, thus, brought to the wire part and to the press section through slots or a perforated face provided on the wall elements.

In the arrangement in accordance with the invention, the replacement air is preferably brought to both sides of the paper/board machine, to the tending side and to the driving side as well as to the top side and to the tending platform, and the removal of the air is carried out through the exhaust arrangements provided in the process, in which case, in the interior of the hood, the air flows out of the space of the tending platforms and from elsewhere in the environment of the machine to the middle of the machine, and then the air in the working area remains dryer and the inner faces of the hood remain clean. In stead, the warm and humid circulation air is brought to the area of the wire and the web, for the circulation air must be as humid as possible in order that the temperatures of the web and the wire should not become lower by the effect of evaporation. In the arrangement, preferably a sufficiently warm circulation air is employed, and at the same time evaporation as well as lowering of the temperatures of the web and the wires are prevented. If necessary, the temperature in the space inside the hood can be raised. The circulation air constitutes a part of the exhaust air of the hood, or it consists of exhaust air from other processes of the paper machine.

The arrangement in accordance with the invention is suitable for use in different paper machines and also in tissue and TAD machines. (In TAD machines, there is no press section proper, for which reason intensified draining in the wire part, of course, provides a remarkably increased rate of production.)

In the arrangement, preferably displaceable hood elements are used. In accordance with an exemplifying embodiment of the invention, the displaceable parts of the hood move preferably in two opposite directions: the displaceable hood element of the wire part towards the wet end of the paper machine and the displaceable hood element of the press section towards the dry end of the paper machine, for example, onto the hood of the dryer section. In the paper machine, at the driving side, preferably a stationary hood walls is used, because the drive gear placed at the driving side requires an abundance of lead-in holes from the interior of the hood to the machine hall. For example, on the wall at the driving side and on the floor of the machine plane at the tending side, for example, rails have been provided, along which the hood is displaced. The hood element is provided with necessary gates etc. doors and windows; for example, in the hood element of the press section, there is a gate for replacement of the wire and/or felt, which gate is, in the open position, placed in the same location as in the hood of the dryer section.

In the arrangement in accordance with the invention, replacement air is brought through the walls, and the flow is guided towards the paper machine. The frame beams in the wet end of the paper machine can be used for the supply of circulation air. According to a preferred feature of the invention, the hood has been arranged as sealed in relation to the rest of the machine hall, in which case the wire part and the press section as well as the machine hall have separate air spaces, as a result of which the requirement of air-conditioning in the hall is reduced, because the heat and moisture load in the machine hall becomes lower. The hood also lowers the noise level in the machine hall at the wet end of the paper machine, because, according to the invention, the elements have been constructed so that the air space between the walls in the element, together with the walls, forms an efficient sound insulation. By means of the hood arrangement in accordance with the invention, considerable economies of energy are obtained. The economies of energy can be enhanced further by means of recovery of heat connected with the hood arrangement, which recovery becomes possible because of the increased humidity and raised temperature of the exhaust air.

According to the invention, the supply of air has been arranged so that the hood construction can be kept sealed. Moreover, in the hood construction, consideration has been given to various operations of servicing, drive and tending and, thus, to accessibility of the wire part and of the press section.

In the following, the invention will be described in more detail with reference to the figures in the accompanying drawing, the invention being, however, not supposed to be strictly confined to the details of said illustrations.

Figure 1 is a schematic side view of the wire part and the press section of a paper machine viewed from the tending side.

Figure 2 is a schematic illustration of the wire part and the press section of the paper machine viewed from the driving side.

Figure 3 is a schematic sectional view of the wet end of the paper machine.

Figures 4A and 4B are schematic illustrations in part of the construction of an element.

Fig. 1 is a schematic illustration of the wire part 110 and the press section 120 of a paper machine viewed from the tending side. The wire part 110 is provided with a tending-side hood wall 10, which can be shifted in the direction indicated by the arrows S₁. The press section 120 is also provided with a hood wall 20, which can be shifted in the direction indicated by the arrows S₂. The hood construction 10,20 is preferably L-shaped and can be shifted along rails fitted, for example, on the wall at the driving side and on the floor at the tending side. Thus, the hood construction 10,20 forms the ceiling and the vertical wall at the tending side as well as the necessary end walls. The portions of the press section 120 placed in the basement 121 are placed inside the hood walls 23. The hood wall 20 of the press section 120 is shifted in the direction of the arrow S₂, for example, onto the hood 30 of the dryer section 130. The hood walls 10,20 at the tending side can be provided with transparent portions so as to maintain a sight connection with the paper machine, and with portions that can be opened and closed for servicing, such as lift gates, slide doors, or equivalent.

Fig. 2 is a schematic illustration of the hood construction on the wire part and on the press section of the paper machine viewed from the driving side. At the driving side, the hood wall 45 is continuous and preferably mounted stationarily in its position. At the driving side, the hood wall 45 is provided with openable doors 47. Through the hood wall 45, lead-in openings are provided for the drives, frame beams, air ducts, and other equipment. The replacement air is passed into the hood wall 45;10,20 through ducts 44,51,52 preferably connected to the hood wall 45 at the driving side (FIG. 3).

Fig. 3 is a schematic sectional view in the direction of width of the machine at the wire part 110, and the illustration shows the stationary hood wall 45 at the driving side as well as the L-shaped displaceable hood wall 10 formed at the tending side, which wall 10, thus, forms the ceiling and the other side wall. The replacement air into the hood is passed from the duct 44 as the air flow A₁, and it is distributed into the ducts 51,62 as the air flows A₂ and A₃, of which the air flow A₂ is blown into the space in the interior of the hood as the flows A₄ through the duct 62 that has been formed in the interior of the fixed hood wall 45, and the flow A₃ is passed from the duct 51 into the duct 52 and further into the duct 62 placed in the interior of the L-shaped hood wall 10, from which it is passed through the blow openings as the flows A₅. Circulation flow is introduced as the inlet flows A₇ into the interior of the hood through the ducts 64 and 65 as the flows A₆. The hood is sealed in relation to the rest of the machine hall, and the displaceable hood walls 10,20 are sealed in relation to the stationary hood wall 45 and to the floor of the machine hall, for example, by means of brush seals or labyrinth seals (not shown in the illustrations). The duct 52 has been made resilient so that displacement of the hood wall 20 does not create problems. The temperature of the replacement air is 40...90 °C, preferably 60...70 °C, and its humidity is 5...30 grams of H₂O per kilogram of dry air, preferably 10...20 grams of H₂O per kilogram of dry air. The temperature of the circulation air is 40...70 °C, preferably 45...55 °C, and its humidity is 50...200 grams of H₂O per kilogram of dry air, preferably 65...115 grams of H₂O per kilogram of dry air.

Fig. 4A is a schematic enlarged illustration in part of an exemplifying embodiment of the construction of the hood wall 10,20,45 in accordance with the invention, in which hood wall there is a continuous sound-insulating and noise-insulating outer wall 61 placed at the side of the machine hall and an inner wall 63 placed inside the hood, between which walls an air duct 62 has been formed, out of which duct 62 the air is passed into the space inside the hood out of slots that have been formed at the joints 67 provided in the inner wall 63. In the exemplifying embodiment of Fig. 4B, separate blow openings 68 have been made into the inner wall 63, through which openings the air is blown into the interior of the hood. The exhaust air is evacuated from the interior of the hood through the exhausts provided in the process of the paper machine.

The inside face of the inner wall 63 of the hood elements 10,20,45 is made of a sheet material, preferably a stainless material, which permits easy cleaning and high strength of the wall 63 face. The lower face of the ceiling can be coated with a suitable material, for example teflon, to improve the cleanliness. Since the air flowing in the interior of the wall is preferably heated, condensed water is not formed on said face. The outer wall 61 of the wall construction is made of an insulating material and of a sheet material, preferably glass wool and aluminum. The thickness of the entire wall construction is 300...500 mm. Besides the preferred exemplifying embodiment described above, the hood walls can also be collapsible or of bellows construction or equivalent. Hoods made for small paper machines may consist of ceiling and wall constructions that can be lifted off.

Above, the invention has been described with reference to some preferred exemplifying embodiments of same only, the invention being, however, not supposed to be strictly confined to the details of said embodiments.