Method and device in drying or cooling of a paper web or equivalent

Abstract: The invention concerns a method in drying and/or cooling of a paper web or equivalent, in which method the web (W) is passed over the circumference of a revolving roll (10) or equivalent on support of a support wire (15) or equivalent on the face of the support wire (15) or equivalent that is placed facing the roll (10), in which method the web (W) is dried and/or cooled by means of a gas. In the method, drying and/or cooling gas is blown through openings (44;45) that have been made into the mantle (12) of the roll (10) into the space between the outer face of the roll (10) and the web (W) supported by the support wire (15) or equivalent, whereby a support zone (11) formed by pressurized gas is formed between the outer face of the roll (10) and the web (W), and that in the method the humidified gas is passed out of the support zone (11) into the interior of the roll (10) through openings (46;47) that have been made into the mantle (12) of the roll (10), into a system of exhaust ducts placed inside the roll (10). Further, the invention concerns a device in drying and/or cooling of a paper web or equivalent, which device is composed of a roll (10) or equivalent, which roll (10) is revolving and which roll (10) is provided with openings (44,46;47,45) placed in the mantle (12), and in the interior of which roll (10) a system of gas ducts (13,14) has been formed, the web (W) to be dried being fitted to run over the circumference of the roll (10) preferably on support of a support wire (15) or equivalent. Into the roll (10) mantle (12), blow openings (44;45) have been fitted so as to form a support zone (11) formed by pressurized gas between the outer face of the roll (10) and the web (W) to be dried, and that in the mantle (12) of the roll (10), there is a second set of openings (46;47) for removal of the humidified gas.

Description: The invention concerns a method in drying and/or cooling of a paper or board web, in which method the web is passed over the circumference of a revolving roll or equivalent on support of a support wire or equivalent on the face of the support wire or equivalent that is placed facing the roll, in which method the web is dried and/or cooled by means of a gas. Further, the invention concerns a device in drying and/or cooling of a paper or board web and/or telt, which device is composed of a roll or equivalent, which roll is revolving and which roll is provided with openings placed in the mantle, and in the interior of which roll a system of gas ducts has been formed, the web to be dried being fitted to run over the circumference of the roll preferably on support of a support wire or equivalent. The highest web speeds in paper machines are currently of an order of 25 metres per second, but before long, the speed range of 25...40 m/s is also likely to be taken into use. Even with the highest speeds that are employed now, and with the ever higher speeds in the future, especially the dryer section has become and will be a bottle-neck for the runnability of a paper machine. FR-A-2 399 504 discloses a device according to the preamble of claim 9. As is known from the prior art, in multi-cylinder dryers of paper machines, twin-wire-draw and/or single-wire draw is/are employed. In the former case, the groups of drying cylinders comprise two wires, which press the web, one from above and the other one from below, against the heated cylinder faces. Between the rows of cylinders, which are usually horizontal rows, the web has free and unsupported draws, which are susceptible of fluttering, which may result in web breaks. In said single-wire draw, each group of drying cylinders comprises one drying wire only, on whose support the web runs through the whole group so that, on the drying cylinders, the drying wire presses the web against the heated cylinder faces, and on the reversing cylinders between the drying cylinders the web remains at the side of the outside curve. Thus, in single-wire draw, the drying cylinders are placed outside the wire loop, and the reversing cylinders inside the loop. In the prior-art normal groups with single-wire draw, the heated drying cylinders are placed in the upper row, and the reversing cylinders are placed in the lower row, said rows being, as a rule, horizontal and parallel to one another. So-called inverted groups with single-wire draw are also known, in which the heated drying cylinders are placed in the lower row and the reversing suction cylinders or rolls in the upper row, the substantial objective being to dry the web from the side opposite in relation to a normal group with single-wire draw. In the following, when the terms "normal (dryer) group" and "inverted (dryer) group" are used, what is meant is expressly the groups with single-wire draw similar to those mentioned above. In the area of the dryer section of a paper machine, various problems have occurred, for which the present invention is supposed to suggest novel efficient solutions. These problems include the large length of the dryer section, which increases the costs of the dryer section and of the machine hall. Problems have also been caused by the difference in speed between the paper web and the wires, which has resulted in wear of the wires and, at the worst, even to paper breaks in the dryer section. Problems may also have occurred in the controllability of the web draw and in the runnability of the web. With respect to the prior art, reference is made to the FI Patent Application No. 2919/71 , wherein a continuous dryer for paper products is described, in which dryer two cylinders with adjustable temperatures are used, which are placed at a short distance from one another on the joint portion of the runs of carrier belts penetrable by air. The belts are guided towards the starting point of their joint run by means of cylinders which blow hot air through their side walls and which cylinders have been called air-blow cylinders. In this prior-art solution, heat is always transferred to the paper by the intermediate of a wire, in which case the wire that is employed must be capable of storage of heat. Further, the wire is penetrable by air, because the preheating takes place by the principle of blowing through the wire. It follows from this that it is always necessary to use a woven metal wire. In this solution, the outlet gas is passed through the wire to outside the cylinder, and the paper is always carried between two wires. In this prior-art solution, the construction of the blow cylinder in itself has not been described, but it has just been stated that, in the cylinders, an inside partition wall is employed. With respect to the prior art, reference is also made to the FI Laid-Open Publication No. 62,573 , in which a dryer for drying a continuous paper-fibre sheet is described. In said dryer, there is a rotatable drum and means for feeding dry gas into the interior of this rotatable drum and means for making the gas to flow out of the rotatable drum. In this solution, the material to be dried is not supported by a wire or equivalent, and the material to be dried runs around the drum on support of strips. The drying gas spreads onto the face of the material to be dried along particular passages placed on the face of the drum, in which passages the gas can spread in the direction of the circumference only, because the strips for supporting the material to be dried separate the passages from one another. The trapeze-like strips parallel to the circumference intensify the flow of the drying gas in the direction parallel to the circumference. In this prior-art solution, the gas distribution equipment is stationary, i.e. the leakages from the drying gas to the outlet gas take place inside the drum. This results in a certain percentage of loss of gas. The object of the present invention is to provide a method and a device in drying of a paper web in which method and device the problems described above have been eliminated or at least minimized. In view of achieving the objectives stated above and those that will come out later, in the method in accordance with the invention, drying and/or cooling gas is blown through openings that have been made into the mantle of the roll into the space between the outer face of the roll and the web supported by the support wire, whereby a support zone formed by pressurized gas is formed between the outer face of the roll and the web, and that in the method the humidified gas is passed out of the support zone into the interior of the roll through openings that have been made into the mantle of the roll, into a system of exhaust ducts placed inside the roll. In the method in accordance with the invention, drying gas is blown, through openings that have been made into the roll mantle, between the outer face of the roll and the web supported by the support wire. An air cushion is formed between the outer face of the roll and the web, the counter-force required by said cushion being produced by using the tension force of the wire as an aid. The humidified gas is passed out of the air cushion into the roll interior through openings that have been made into the outer circumference of the roll, into the system of exhaust ducts placed inside the roll. The device in accordance with the invention is mainly characterized in that, into the roll mantle, blow openings have been fitted so as to form a support zone formed by pressurized gas between the outer face of the roll and the web to be dried, and that in the mantle of the roll, there is a second set of openings for removal of the humidified gas and passing the gas into a system of exhaust ducts placed inside the roll. In the arrangement in accordance with the invention, the gas is blown directly against the material to be dried, and the exhaust gas is removed directly between the holes or slots. Owing to the unified construction of the roll or drum that forms the device, no gas is lost, i.e. there is no loss percentage. By means of the method and the device in accordance with the invention, during the progress of the drying process, it is also possible to cool the material to be dried in between in order to obtain a better drying capacity. This is also permitted by the condition of the surrounding air (no risk of condensation). When an arrangement in accordance with the present invention is used, a dryer section is obtained whose length is even just half the length of the dryer section in the prior-art solutions. In the directions of height and width of the dryer section, the geometry of the dryer group can be constructed in accordance with the requirements of the wet end of the machine. Moreover, the arrangement in accordance with the invention does not require extensive investments, and it can also be used in modernizations of existing paper machines. The arrangement in accordance with the invention is easy to operate, because the devices can be placed in a number of different ways so that, for example, the present, conventionally known tending platform is employed. All points of discontinuity, such as group gaps, are placed at viewing height from the tending platform. The running and the mode of drying in accordance with the invention permit the use of rolls of large diameter and even rolls of different diameters in one group. They permit a machine geometry in which the runnability can be improved and the machine speed be increased further. Since blowing from the drum is needed during drying only, the auxiliary operations (such as threading) can be carried out without blowing of gas or heating. In this way the consumption of energy is minimized and the external conditions are improved. The rolls have common or individual drives. An individual drive of a roll permits a circumferential speed of the roll different from the speed of the web. This possibility prevents, for example, blow marking. In the arrangement in accordance with the invention, no closed hood is needed, in which case the accessibility during operation of the paper machine is better than in the prior-art solutions. In the invention, a pervious or impervious wire is used. Likewise, the wire may be heat-conductive or non-conductive. The range of the material to be dried may vary from the thickest board grades to thinner printing papers, tissue paper, or any material whatsoever to be dried that can be bent around the drum. Even if, in the present description, the method and the device in accordance with the invention are described mainly as applied to the dryer section of a paper machine, it is understood that the invention is also suitable for drying applications of other types, such as drying a coating on a paper or equivalent, in which, at the side of the coating, there must be a contact-free draw, and, for example, drying of felts or equivalent, drying of various web-like materials from the thickest board grades to the thinnest printing paper, the only limitation being the flexibility of the material to be dried. In the following, the invention will be described in more detail with reference to the figures in the accompanying drawing, in which Figure 1A is a schematic sectional view of the device in accordance with the invention in the cross direction. Figure 1B is a schematic sectional view of the device in accordance with the invention in the longitudinal direction. Figure 2A is a schematic axonometric view of the device in accordance with the invention, Figure 2B is a schematic longitudinal partial sectional view that illustrates the arrangement in accordance with the invention, Figure 2C shows exemplifying embodiments of blow openings for use in the device in accordance with the invention, Figure 3A is a schematic partial sectional view of an exemplifying embodiment of the arrangement in accordance with the invention, Figure 3B is a longitudinal partial sectional view of a second exemplifying embodiment of the arrangement in accordance with the invention, Figures 4A...4B are schematic longitudinal sectional views of exemplifying embodiments of wire guides for use in connection with the device of the invention, Figures 5A...5B are schematic partial sectional views in the cross direction of the device in accordance with the invention, Figures 6A...6B show a schematic exemplifying embodiment for covering the free area of the roll in the arrangement in accordance with the invention, Figure 7 shows a flow diagram of the drying gas, Figures 8A...11R illustrate different geometries in which the device in accordance with the invention is applied, Figure 12 shows an exemplifying embodiment of the invention, and Figure 13 shows an exemplifying embodiment of the invention. The device in accordance with the invention that is shown in Figs. 1A...1B is a roll 10, cylinder, drum, or equivalent, whose mantle 12 is provided with holes 44,46. Into the interior of the roll 10, a drying gas P in is passed, which is blown through the holes 44 onto the face of the material W to be dried, such as paper. Since the paper W is supported by the wire 15, a pressure is produced between the outer face of the roll 10 and the paper W. By means of a suitable compression pressure, the paper W is separated from the roll 10 face, which permits a flow of the drying gas, which is usually heated air, from the inlet holes 44 into the outlet holes 46, and the drying process proper is carried out. With a suitable blow pressure, which depends on the force applied by the wire 15 to the paper W, i.e. on the wire tension, a support zone formed by pressurized gas, a so-called air cushion 11, is produced between the outer face of the roll 10 and the paper W supported by the wire 15, which air cushion supports and dries the paper W. The gas/air that is blown is dry and heated and, thus, binds humidity. The blow pressure is 500 Pa ... 10,000 Pa, preferably 1000 Pa ... 5000 Pa, and the temperature of the drying gas is 20 °C ... 500 °C, preferably 100 °C ... 400 °C. The humid gas is removed from the support zone 11 through the outlet holes 46 placed between the blow holes 44. The blow holes 44 extend almost across the entire width of the paper W, but the suction holes do not, because a control of the lateral areas of the paper W requires an outflow P Z between the roll 10 face and the paper W in this exemplifying embodiment of the invention. The rest of the roll 10 face, except the gas flow openings 44,46, may be smooth or grooved. The grooves may be placed in the longitudinal direction or in the cross direction of the roll 10 mantle, or between said directions, i.e. diagonal. The grooves may also be radial in relation to the blow or exhaust openings 44,46. The drying gas P in is passed through the system of ducts 13 through the holes 44 in the face of the roll 10 mantle 12 into the zone between the outer face of the roll 10 and the paper W, in which zone an air cushion 11 is formed. Since there are no exhaust holes 46 in the end area A S of the roll mantle, the exhaust air P Z is discharged out of the gap between the roll 10 face and the paper W into the stationary outlet 35. In the middle area A 1 of the roll 10 mantle 12, between the intake holes 44, there are exhaust holes 46, through which the gas that has bound the moisture of the paper W is removed along the system of exhaust ducts 14 to the interior of the roll 10 and from there further out as the exhaust gas P out . In Figs. 1A...1B and in the following figures, the arrows denote the flow direction of the gas flow unless otherwise stated. The paper web W that is supported by the wire 15 is guided over the guide roll 61 onto the face of the drying roll 10. The roll revolves in the sense indicated by the arrow S and, after the paper W has passed, on support of the wire 15, around the substantial circumferential area of the roll 10, it is passed by means of the other guide roll away from the roll face to further drying or to finishing. The area that is not covered by the web W is closed by means of a closing member 25. The roll 10 revolves at a speed substantially equivalent to the running speed of the paper web and the wire. In some exemplifying embodiments of the invention, after the air cushion 11 has been formed, the speed of rotation of the roll can be slowed, and the rotation of the roll 10 can be even stopped. In the exemplifying embodiment of the invention as shown in Figs. 2A...2B, the supply P in of the drying gas into the roll 10 is accomplished through the openings 16 placed at the ends of the roll 10, two different exemplifying embodiments of said openings being illustrated in Figs. 4A...4B. In Fig. 2A, for the sake of example, a slot-shaped blow opening 45 and a slot-shaped exhaust opening 47 are also shown. When the roll 10 revolves in the sense indicated by the arrow S, the drying gas that was passed in through the feed openings 16 is blown out through the roll 10 face through the blow holes 44 or blow slots 45, in which case a support zone, a so-called air cushion 11, consisting of pressurized gas is formed between the paper W and the outer face of the roll 10, out of which air cushion the gas, humidified by the moisture of the paper W, is removed through the exhaust holes 46 or exhaust slots 47 into the roll 10 interior, from where it is passed to the outlet as exhaust gas P out . As is the case in the exemplifying embodiment of the invention as shown in Figs. 1A...1B, there are no exhaust holes 46 in the lateral areas of the roll 10 mantle 12, or the exhaust slot 47 has been formed substantially shorter in the lateral areas, in which case a part of the gas is removed as the exhaust P Z out of the lateral areas of the roll 10. Fig. 2B is a schematic longitudinal sectional view of the roll 10. Below the wire 15, there is the paper web W, below which an air-cushion zone of about 0.5...10 mm, preferably 2...4 mm, is formed. The diameter of the blow holes 44 in the roll 10 mantle 12 is about 1.0...10 mm, preferably 2...5 mm, and the diameter of the exhaust-air holes is about 10...100 mm, preferably 20...60 mm. When slot-shaped blow openings are used, their length is substantially equal to the width of the paper web, and their width is 1.0...20 mm, preferably 2.0...6.0 mm, and the length of the slot-shaped exhaust openings is shorter than the width of the paper web, and their width is 5.0...50 mm, preferably 10.0...25 mm. The diameter of the blow roll 10 is 0.5...10.0 m, preferably 1.5...6.0 m. Fig. 2C illustrates the operation of a single blow hole 44. When the pressure of the air that is blown exceeds the tension force of the band 15 that supports the material W to be dried, the material to be dried is separated from the roll 10 face. A carrier-face zone, i.e. a so-called air cushion 11, is formed, whose thickness is 0.5...10 mm, preferably 1.5...5 mm, and the gas can flow in the hole 44. Now the drying effect of the gas also starts. The gas collides against the material W to be dried at a velocity of 30...150 m/s, preferably 50...120 m/s, and turns then so that it becomes parallel to the material W to be dried. During the entire flow of the gas, water is bound from the material W to be dried to the gas. This cooled gas of higher humidity is passed out through separate exhaust holes 46. The dimensioning of the amount of gas to be blown is based on the consumption of blowing energy in comparison to the heat-transfer coefficient that is obtained. The optimal area of the holes is indicated as a percentage of the whole area of the roll 10 mantle 12. The values that are used are 0.2...5 %, preferably 0.5...2.5 %. Attempts are always made to maximize the effective area (length on the circumference of the drum), but the other aspects of the runnability of the web W impose certain limitations on it. The covering angle is, as a rule, 180...350°, preferably 250...330°. According to Fig. 2C, the blow openings in the roll 10 mantle 12 may be straight openings 44 or openings 44'' or 44"' provided with a widening. The size of the opening for the inlet gas of the roll 10 and of the opening for the outlet gas, placed at the opposite end of the roll 10, as shown in Figs. 1B and 2A, has been chosen so that the velocity of the gas at the opening is 5 m/s ... 50 m/s, preferably 15 m/s ... 35 m/s. Figs. 3A...3B show exemplifying embodiments in which the effective part of the paper W and the wire 15 are supported by the air cushion 11, and the edges of the wire 15 (FIG. 3A) or the edges both of the paper W and of the wire 15 (FIG. 3B) are supported by the support faces 17 formed on the mantle part 12 of the blow roll 10. In these exemplifying embodiments, all the exhaust air is passed out of the area of the air cushion 11 through the exhaust openings 46. Figs. 2B, 3A and 3B illustrate the most important exemplifying embodiments of the invention: Fig. 2B shows a method in which a smooth roll face is employed, in which case a part of the gas is removed as the exhaust flow P Z from the lateral areas of the roll 10, where both the wire 15 and the paper W are completely supported by the air cushion 11; in the embodiment shown in Fig. 3A, the paper W is completely supported by the air cushion 11, but the wire 15 is supported on the support faces 17, and in Fig. 3B both the paper web W and the wire 15 are supported by the support faces 17. According to what is shown in Figs. 4A...4B, the blow air or gas is passed into the roll 10 through the duct 41 into the system of ducts 13 and further into the blow openings 44, and the humidified exhaust gas is passed through the system of ducts 14 to the exhaust 43 through the exhaust pipes or passages 46 out of the roll 10. In the exemplifying embodiment shown at the top in Fig. 4A, the wire 15 guide members 51 are attached to the ends in the lateral areas of the roll 10 mantle 12, and their 51 positions are adjustable. At the bottom in Fig. 4A, the wire guides 52 have been formed as fixed in the lateral areas of the roll 10 mantle 12. At the top in Fig. 4B, there is a convex wire 15 guide face 23, and at the bottom a concave wire guide face 24. In this connection it should be pointed out that the wire guides or guide faces should not be confused with the support faces described above. Fig. 5A is a sectional view taken along the line A-A in Fig. 4A, wherein the system of air ducts 13 placed inside the roll 10 are shown, which ducts 13 pass into the blow openings 44, and the system of exhaust ducts 14, into which the humidified gas is passed through the exhaust openings 46. Fig. 5B is a schematic sectional view taken along the line B-B in Fig. 4B, in which drying gas is passed out of the duct 13 through two blow openings 44 out through the roll 10 mantle face 12, and the humidified air is removed through the exhaust openings 46 to inside the roll 10 mantle face 12. According to what is shown in Figs. 6A...6B, the free portion of the blow roll 10, i.e. the area that remains outside the portion covered by the wire 15 and by the paper W, is closed by means of a closing member 25 so as to reduce leakages. The closing member 25 may be a separate device, such as is shown in the figures, or the area is closed in the longitudinal direction between the reversing rolls 61 (Fig. 1) and in the cross direction by means of ends (not shown) formed by the blow roll 10 and the reversing rolls 61. The closing member 25 includes a sealing against the blow roll 10, which sealing is carried out by means of a mechanical seal 26 or by means of a sealing counter-blowing 27. In the sealing counter-blowing 27, blower air or compressor air is employed. At the points of inlet and outlet of the material W to be dried onto and off the blow roll 10, there is counter-blowing P X in the pressure nip N+ at the inlet side of the web W and in the vacuum nip N- at the outlet side to prevent the air cushion 11 from being discharged. The counter-blowing device may be integrated, e.g., with the closing member 25, or it may be a separate device. The cleaning of the blow roll 10 takes place by means of counter-blowing P 1 against the roll 10 face. For the blowing P 1 , it is possible to use blower air or compressor air, and the cleaning equipment 28 may be placed in the closing member 25 or be a separate device. Fig. 7 shows the flow diagram of the drying gas, such as heated air. Since the air-cushion principle requires that the drying gas is also pressurized at the discharge opening 46, the state of the entire gas of higher humidity that is discharged is pressurized. Thus, the whole of the interior of the revolving blow roll 10 and the gas distributor devices outside said roll are pressurized. The system requires just one blower 37 to feed the gas. By regulating the blower system 37, the desired pressure state of the gas is obtained by means of the regulator 67, or the gas flow is obstructed at the discharge side by means of the regulator 49. The gas that is discharged can be passed, for example, through heat recovery to the open air, or a part of the gas can be recirculated to among the gas to be blown in. In Fig. 7, the reference numeral 29 denotes the stationary gas distributor equipment, which is sealed in relation to the roll 10 by means of the seals 38. The gas flow is illustrated by means of arrows. The drying gas is passed into the drying-gas inlet 41 in the gas distributor equipment 29 of the roll, from which it is passed through the set of ducts 13 into the blow holes 44. The humidified gas, which is removed through the exhaust holes 46, is passed through the set of exhaust ducts 14 to the outlet 43, from which it is passed further through the gas distributor equipment 42 to the outlet duct 48, which is provided with a regulation member 49 and from which the gas is passed to the open air or a part of the gas is recirculated to among the gas to be blown in, into the duct 68. In the following Figs. 8A...11R, different geometries of the dryer section with the use of the device 10 in accordance with the invention are illustrated. In the figures, the solid line represents the material W to be dried, which is usually paper, board or equivalent, the dashed line represents the blow roll 10 and the guide roll 61, which may be smooth, grooved, or a suction roll, and the dashed-dotted line represents the support band 15, which is most commonly a wire or equivalent. Figs. 8A...8D illustrate exemplifying embodiments in which twin-wire draw is employed. The upper wire is denoted with the reference 15y and the lower wire with 15a. The wire guide rolls are denoted with the reference numeral 61. The closing member of the free portion of the roll 10 is denoted with the reference numeral 25. In Fig. 8A, in connection with the roll 10, one intermediate roll 61 has been fitted in the embodiment shown to the left, and two intermediate rolls 61 in the embodiment shown to the right. When two intermediate rolls 61 are employed, a better support of the paper W is obtained over the free gap W 0 . In the embodiment of Fig. 8B, the effective blow area of the blow roll 10 has been maximized, in which case a closing member 25 is needed in a little area only, and a greater number of blow rolls 10 can be placed in the same wire group. The group has a closed draw, i.e. the paper W is constantly supported by a wire 15a, 15y. Fig. 8C shows an embodiment that is mainly similar to Fig. 8B, but an open draw is employed, in which the paper W is transferred from one blow roll 10 onto the other without a wire, as open draws W 0 . Fig. 8D shows a twin-wire draw in which the effective blowing of the blow roll 10 has been maximized and in which a greater number of blow rolls 10 can be fitted in the same wire group. A closed draw is employed, and a geometry of low height is obtained, because the blow rolls 10 are placed close to one another in the vertical direction. In addition to the intermediate rolls 61, in order to guide the wire 15a, 15y, auxiliary rolls 58 are employed. Fig. 9A shows an embodiment in which, in single-wire draw, one intermediate roll 61 is fitted in connection with the roll 10. Fig. 9B shows an embodiment in which, in single-wire draw, there are two intermediate rolls 61 in connection with the roll 10, by whose means a large coverage of the blow roll 10 is obtained. Fig. 9C shows an inverted arrangement with single-wire draw, in which, in connection with the blow roll 10, the wire 15 is guided by two intermediate rolls 61, in which arrangement an advantage is the large coverage of the blow roll. Fig. 9D shows an inverted arrangement with single-wire draw, in which the wire 15 is guided by one intermediate roll 61 fitted as interlocked between the blow rolls 10. It is a feature common of the exemplifying embodiments shown in Figs. 10A...10D that single-wire draw is used and the web W is passed from blow roll 10 to blow roll 10. Depending on the geometry, either in connection with the upper blow rolls 10 or in connection with the lower blow rolls 10, the support band 15 is the member that receives the blowing. This is why the band 15 should preferably be capable of conducting heat, in which case the drying or cooling effect is transferred to the paper W by the intermediate of the band 15, and, in order that it could be secured that the material to be dried remains in contact with the band, the band is preferably impenetrable by air. This mode of running may also be employed with such materials to be dried as require an adequate contact with the support band both in the longitudinal direction of the web and in the cross direction so as to guarantee the quality or equivalent. In the exemplifying embodiment shown in Fig. 10A, supported by the wire or the band 15, the web W is passed from the blow roll 10 of the upper row onto the blow roll 10 of the lower row and so forth. In the lower row, the paper web W is placed outside. By means of this solution, a low geometry is obtained, but the coverage by the web W is not very wide. In Fig. 10B, an exemplifying embodiment based on a geometry with single-wire draw is shown, in which, in order to increase the coverage proportion and to guide the band or the wire 15, intermediate rolls 61 are employed. On the blow roll 10 in the lower row, the paper web W is placed outside. By means of this solution, a good coverage but a rather high geometry are obtained. In the exemplifying embodiments shown in Figs. 10C...10D, in respect of the paper placed outside on the blow rolls 10 in the upper row, a device 69 is used that applies a normal stationary drying technique, for example infrared drying, blowing or equivalent or cooling, and, if necessary, such a device can also be employed in the other exemplifying embodiments shown in the figures. In the other respects the embodiments shown in Figs. 10C...10D are similar to those shown in Figs. 10A... 10B, even if, in them the paper web W is outside on the upper-row blow roll. The blow roll in accordance with the invention is well suitable for the drying of a coating on paper or equivalent, in which case it is desirable to use so-called contact-free drying at the side to be dried (FIG. 13). Drying by means of a blow roll can also be applied to the current steam-heated cylinder geometries, and stationary heating can be carried out, for example, by means of blow, infra, or equivalent separate devices, which can be applied to all the geometries illustrated in the following Figs. 11A...11R, in which the rolls in the dryer group arrangements in themselves known are denoted with the reference numeral 73. Fig. 11A shows an embodiment with single-wire draw, in which the wire 15 supports the web W that runs over the blow roll 10. The effective blow angle of the blow roll 10 is the same as with the other cylinders 73. Fig. 11B shows a single-wire draw in which the wire 15 guides the web W over the blow roll 10, in connection with which two intermediate rolls 61 are fitted. The effective blow angle of the blow roll 10 has been maximized. In the embodiment with single-wire draw shown in Fig. 11C, a stationary dryer device 69 is also used. The effective blow angle of the blow roll 10 is the same as that of the cylinders 73. In the embodiment with single-wire draw shown in Fig. 11D, the effective blow angle has been maximized. Fig. 11E shows an embodiment inverted in comparison to that shown in Fig. 11A. The solution of Fig. 11F is similar to Fig. 11B as inverted. Fig. 11G is similar to Fig. 11C as an inverted arrangement. Fig. 11H shows an inverted arrangement corresponding to Fig. 11D. Fig. 11I shows an embodiment with twin-wire draw in which the effective blow angle of the blow roll 10 is the same as with the other cylinders 73. Fig. 11J shows an embodiment with twin-wire draw in which the effective blow angle of the blow roll 10 has been maximized. Fig. 11K shows an embodiment with twin-wire draw in which the effective blow angle of the blow roll is the same as with the other cylinders. In the embodiment with twin-wire draw shown in Fig. 11L, the effective blow angle of the blow roll 10 has been maximized. In the embodiment with twin-wire draw shown in Fig. 11M, the blow roll 10 is placed in the upper row of cylinders, the rest being similar to Fig. 11I. In the embodiment with twin-wire draw shown in Fig. 11N, the blow roll 10 is placed in the upper row of cylinders, the rest being similar to Fig. 11J. In the embodiment with twin-wire draw shown in Fig. 110, the blow roll 10 is placed in the upper row of cylinders, the rest being similar to Fig. 11K. Fig. 11P corresponds to Fig. 11L as an embodiment with twin-wire draw, the blow roll 10 being placed in the upper row. Fig. 11Q illustrates an application to a prior-art existing dryer section in which steam-heated drying cylinders 73 are used. The figure shows an embodiment with twin-wire draw, in which an upper wire 15 y and a lower wire 15 a are employed, and the arrangement in accordance with the present invention has been accomplished in connection with the lower wire 15 a , where a blow roll 10 in accordance with the invention is placed, which roll 10 is preferably placed in the place of the first or last cylinder in a normal dryer group. Fig. 11R shows an embodiment corresponding to Fig. 11Q, in which the blow roll 10 is placed in connection with the upper wire 15 y . One blow roll 10 can also form a group of its own. In the dryer section, there may be several such groups, either with an upper wire or with a lower wire. As is shown in Fig. 12, a blow roll 10 in accordance with the invention may also be used for the drying of various felts and equivalent materials. As an example should be mentioned the press felts of paper machines that are used currently. In the drying, it is unimportant if the felt 80 to be dried is pervious to air or impervious, nor is the thermal conductivity of the felt of decisive importance. With a felt penetrable by air, the drying takes place partly as through blowing. The rest of the drying, like the drying of paper, takes place by the air-cushion principle provided by means of a roll 10 in accordance with the invention. Fig. 13 shows an embodiment in which an arrangement in accordance with the invention is used in the drying of a coated paper web W or equivalent. The coated side C of the paper web W runs as a contact-free draw over the blow rolls 10 on support of the wire 15 and carried by the air cushion 11. 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. Many variations and modifications are possible within the scope of the invention defined in the following patent claims.

Claims: A method in drying and/or cooling of a paper or board web, in which method the web (W) is passed over the circumference of a revolving roll (10) on support of a support wire (15) or band on the face of the support wire (15) that is placed facing the roll (10), in which method the web (W) is dried and/or cooled by means of a gas, whereby in the method, drying and/or cooling gas is blown through openings (44;45) that have been made into the mantle (12) of the roll (10) into the space between the outer face of the roll (10) and the web (W) supported by the support wire (15) or band, whereby a support zone (11) formed by pressurized gas is formed between the outer face of the roll (10) and the web (W), and in the method the humidified gas is passed out of the support zone (11) into the interior of the roll (10) through openings (46;47) that have been made into the mantle (12) of the roll (10), characterized in that the humidified gas is passed through the openings (46;47) into a system of exhaust ducts placed inside the roll (10). A method as claimed in claim 1, characterized in that, in the method, the web (W) to be dried is passed so that it runs on support of a support zone (11) at a distance from the roll (10) face. A method as claimed in claim 1 or 2, characterized in that, in the method, a thin support zone (11) is formed, whose thickness is 0.5...10 mm, preferably 2...4 mm. A method as claimed in any of the claims 1 to 3, characterized in that the pressurized support zone (11) formed between the roll (10) and the web (W) is produced by means of the counter-force of the tension of the support wire (15) or band. A method as claimed in any of the claims 1 to 4, characterized in that the speed of the web (W) is determined on the basis of the speed of the support wire (15) or band in which case the speed of the roll (10) may be different from the speed of the web (W). A method as claimed in any of the claims 1 to 5, characterized in that, in the support zone (11), a thermally conductive support wire (15) or band that is impenetrable by gas is heated, the heat being transferred as contact drying from the support wire (15) or band to the web (W) to be dried. A method as claimed in any of the claims 1 to 6, characterized in that, in the method, the free portion of the outer circumference (12) of the roll (10) is closed so as to prevent the support zone (11) from being discharged. A method in drying and/or cooling of a felt, in which method the felt (80) is passed over the circumference of a revolving roll (10) or cylinder or drum, in which method the felt (80) is dried and/or cooled by means of a gas, whereby in the method, drying gas is blown through openings (44;45) that have been made into the mantle (12) of the roll (10) into the space between the outer face of the roll (10) and the felt (80), whereby a zone (11) formed by pressurized gas is formed between the outer face of the roll (10) and the felt (80), and in the method the humidified gas is passed out of the support zone (11) into the interior of the roll (10) through openings (46;47) that have been made into the mantle (12) of the roll (10) characterized, in that the humidified gas is passed through the openings (46;47) into a system of exhaust ducts placed inside the roll (10). A device in drying and/or cooling of a paper or board web and/or felt, which device is composed of a roll (10), which roll (10) is revolving and which roll (10) is provided with openings (44,46;47,45) placed in the mantle (12), and in the interior of which roll (10) a system of gas ducts (13,14) has been formed, the web (W) and/or felt to be dried being fitted to run over the circumference of the roll (10) preferably on support of a support wire (15) or band, whereby, into the roll (10) mantle (12), blow openings (44;45) have been fitted so as to form a support zone (11) formed by pressurized gas between the outer face of the roll (10) and the web (W) and/or felt to be dried, and that in the mantle (12) of the roll (10), there is a second set of openings (46;47) for removal of the humidified gas, characterized in that said second set of openings (46;47) passes the humidified gas into a system of exhaust ducts placed inside the roll (10). A device as claimed in claim 9, characterized in that, in connection with the roll (10), a closing member (25) is fitted, which is placed on the free portion of the roll (10) so as to prevent the support zone (11) from being discharged. A device as claimed in claim 9 or 10, characterized in that, in the outer face of the roll (10) mantle (12), in its lateral areas, belt guides (51) are fitted. A device as claimed in any of the claims 9 to 11, characterized in that the lateral areas of the outer face of the roll (10) have been formed as support faces (17), which carry the edges of the support wire or band (15) that supports the material (W) to be dried. A device as claimed in any of the claims 9 to 12, characterized in that, in the lateral areas of the outer face of the roll (10), support faces (17) have been formed, which carry the edges of the material (W) to be dried and of the support wire that supports said material (W).

Inventors: VUORINEN VESA, VUORINEN, VESA
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1995
Main classification: D21F5
IPC codes: D21F5