A drying system for a machine for producing a paper tissue web

Abstract

The invention relates to a drying system (100) adapted to form a part of a machine for producing a paper tissue web (W). The system comprises a drying hood (8) for a drying cylinder (1), and an applicator (7). The applicator (7) presents a plurality of applicator portions (7a, 7b, 7c) distributed across the width of the web (W), each applicator portion (7a, 7b, 7c) being adapted to apply a portion of air guided from the drying hood (8) to a width segment of the web (W), wherein the drying system (100) comprises an application adjustment arrangement (110) arranged to individually adjust the humidity and / or the temperature of the air applied to the web (W) by each applicator portion (7a, 7b, 7c).

Description

[0001] A DRYING SYSTEM FOR A MACHINE FOR PRODUCING A PAPER TISSUE WEB

[0002] TECHNICAL FIELD

[0003] The invention relates to a drying system for a machine for producing a paper tissue web, for applying air to a moving paper tissue web manufactured by the machine.

[0004] BACKGROUND

[0005] In tissue manufacturing technology, there is a desire to increase the productivity of machines for producing paper tissue webs, and / or reduce the energy consumption of such machines. For reducing the energy consumption, hot process air from one stage of the machine process may be used in another stage of the machine process.

[0006] US9702084B2 describes a machine for making a tissue paper web. A first hood is arranged opposite a suction roll. A Yankee drying cylinder is covered by a second hood, and hot exhaust air from the second hood is fed through a conduit to the first hood and used to supply the first hood with moist hot air. The moist air is then sucked through the tissue paper web by the suction roll such that moisture condensates on the tissue paper web and thereby raises the temperature of the tissue paper web before it passes through an extended nip. Thereby water in the web may be less viscous and thereby more easily removed by the suction roll.

[0007] US5385644A describes a soft-tissue paper machine with a blow device with a blow chamber. Exhaust air from a Yankee hood is used as a source of energy for the blow device. By means of the blow device, it is possible to correct an uneven moisture profile of the paper web by dividing or partitioning the blow chamber into several blocks, in which the blow velocities are regulated individually by means of regulation members indicated as dampers in the drawings.

[0008] There is nevertheless a desire to further reduce energy consumption or increase productivity of machines for producing paper tissue webs. SUMMARY

[0009] An object of the invention is to reduce energy consumption and / or increase productivity of a machine for producing a paper tissue web.

[0010] The object is reached with a drying system adapted to form a part of a machine for producing a paper tissue web. The drying system comprises an applicator and a drying hood for a drying cylinder, such as a Yankee cylinder, arranged to engage a moving paper tissue web, wherein the system is adapted to guide air from the drying hood to the applicator adapted to apply the air to the web. The applicator presents a plurality of applicator portions distributed across the width of the moving paper tissue web, each applicator portion being adapted to apply a portion of the air guided from the drying hood to a width segment of the moving paper tissue web. The drying system comprises an application adjustment arrangement arranged to individually adjust the humidity, and / or the temperature of the air applied to the moving paper tissue web by each applicator portion.

[0011] The air guided from the drying hood to an applicator may be hot processing air. For this a duct may lead to the applicator, from a return duct in a circulation system for the drying hood, from an exhaust duct leading from the return duct or the drying hood, or from the drying hood itself. The applicator may be adapted to extend across the width of the web, i.e. in a web width direction which is transverse to a direction of movement of the web. One or more air inlets for the reception of the air in the applicator may be connected to one or more air outlets of the drying hood via one or more conduits.

[0012] The drying system may comprise a nip, e.g. an extended nip, and / or a suction roll, arranged so that the web passes through the nip or the suction roll, before reaching the drying cylinder. By applying the process air to the web before the web reaches the nip and / or the suction roll, the web temperature increases and its water viscosity decreases. Thereby, where a nip and / or a suction roll is provided before the drying cylinder, the paper sheet may reach a higher or lower dryness content after the nip and / or the suction roll. By the invention, the applicator is provided with a web moisture profiling capability. Thereby, the humidity profile in the web cross direction will be controlled by the applicator portions which control the characteristics, such as the temperature and / or humidity, of the air applied to the respective width segment of the web. In this way it is possible to influence the Dryness After Press Profile or the PPRC (Post Press Roll Consistency) profile and correct and improve the final moisture profile at a reel reached by the web after the drying system. Thereby, a bad moisture profile at the reel, and a need to correct it by over-drying the paper, which in turn leads to a bad paper quality or a bad paper machine runnability, can be avoided. Avoiding such a correction of the moisture profile at the reel avoids an increased energy consumption connected to it. Thus, by securing a more even PPRC profile entering the drying cylinder, there is no need to over-dry the paper exiting the drying cylinder. Thereby, the drying load on the drying hood is reduced, whereby the energy consumption of the machine is decreased and / or more energy will be available to increase the productivity of the machine. Also, a more even humidity profile across the web will secure that also the water viscosity is even when the web engages the drying cylinder. Thereby, drying process will be more effective, allowing a reduction of the hot air application by the drying hood. Thereby, more energy may be available for the applicator through the hood process air. Thereby a synergistic effect is provided in which the profiling capacity increases the energy provided for its function. Thereby, the overall energy consumption of the machine is decreased.

[0013] By the application adjustment arrangement according to the invention being arranged to individually adjust the humidity, rather than the flow, of the air applied to the web by the respective applicator portion, the control of the humidity profile across the web can be performed without energy losses created by activation of dampers for the flow control.

[0014] Also, the system according to the invention allows for a bidirectional control of the humidity of the air applied by the respective applicator portion. For example, when an increase in paper moisture is required in specific areas, the average humidity of the applied air may be reduced. Conversely, when a decrease in paper moisture is needed, the humidity of the applied air may be raised. Such a dual-action capability allows for independent and localized adjustments across different segments of the paper web, providing an ability to effectively modulate the energy delivered across the paper web. Thereby full control over the moisture profile is enabled with a high degree of precision. Thereby, the avoidance of an energy consumption increase, caused by a correction of the web moisture profile, as mentioned above, may be further secured.

[0015] In some embodiments, the application adjustment arrangement is arranged to individually adjust the humidity of the air applied to the moving paper tissue web by each applicator portion. In some embodiments, the application adjustment arrangement is arranged to individually adjust, in addition to the humidity, the temperature of the air applied to the moving paper tissue web by each applicator portion. In some embodiments, the application adjustment arrangement is arranged to individually adjust, in addition to the humidity and / or the temperature, the flow of the air applied to the moving paper tissue web by each applicator portion. Thereby, the system may be adapted to guide the air to the applicator portions via respective portion conduits, wherein the applicator application adjustment arrangement comprises dampers in the portion conduits. This provides a possibility to adjust the flow characteristics in each applicator portion. In some embodiments, the portion conduits are equipped with respective flow meters with the purpose to continuously measure and control the air flow to the respective applicator portion.

[0016] However, in other embodiments, the application adjustment arrangement is not arranged to individually adjust the flow of the air from the drying hood applied to the moving paper tissue web by each applicator portion. Thereby, the use of dampers for such individual flow adjustment may be omitted. This is beneficial since the use of dampers to individually regulate the flow will cause pressure drops over the dampers. These pressure drops translate into energy losses. This is counter to an aim to reduce energy consumption of the machine. In particular, such energy losses counteract the avoidance of an energy consumption increase, caused by a correction of the web moisture profile, as mentioned above. Also, such energy losses counteract the energy recovery obtained by guiding the air from the drying hood to the applicator.

[0017] Moreover, a gradual activation of any of such dampers so as to reduce the flow, will allow only an increase, but not a decrease, of the paper moisture content at the respective blow chamber block. By the application adjustment arrangement being arranged to individually adjust the humidity, rather than the flow, of the air applied to the web by the respective applicator portion, the control of the humidity profile across the web can be performed without energy losses created by activation of dampers for the flow control.

[0018] Also, embodiments of the invention allow for a bidirectional control of the humidity of the air applied by the respective applicator portion. For example, when an increase in paper moisture is required in specific areas, the average humidity of the applied air may be reduced. Conversely, when a decrease in paper moisture is needed, the humidity of the applied air may be raised. Such a dual-action capability allows for independent and localized adjustments across different segments of the paper web, providing an ability to effectively modulate the energy delivered across the paper web. Thereby full control over the moisture profile is enabled with a high degree of precision. Thereby, the avoidance of an energy consumption increase, caused by a correction of the web moisture profile, as mentioned above, may be further secured.

[0019] Preferably, the applicator comprises, for each applicator portion, a portion envelope forming a portion cavity, wherein each portion envelope is adapted to distribute the air across the respective width segment of the web. In some embodiments, the applicator presents a cavity which is divided by separation walls into the portion cavities. One or more distribution plates may be attached to the portion cavities, the distribution plates comprising a plurality of distribution holes arranged adjacent one another along the width segment of the moving paper tissue web and a plurality of distribution holes arranged adjacent one another along the length of the moving paper tissue web.

[0020] In some embodiments, each applicator portion is adapted to receive, in addition to the respective portion of the air from the drying hood, additional air, wherein the flow of the additional air to each applicator portion is individually adjustable. The system may comprise an air mover for generating the flow of additional air. The additional air may be fresh air. The additional air may have an ambient temperature, e.g. 10-30 degrees C. The additional air may be guided to the respective applicator portion via a respective additional air conduit. The additional air may be mixed with the air from the drying hood before the mixture is applied to the respective segment of the web. Thereby, the temperature and / or the humidity of the air applied to the web may be controlled individually for each applicator portion.

[0021] In some embodiments, each applicator portion is adapted to receive, in addition to the respective portion of the air from the drying hood, steam, wherein the flow of the steam to each applicator portion is individually adjustable. The system may comprise a steam generator for generating the flow of steam.

[0022] The steam may be guided to the respective applicator portion via a respective steam conduit. The steam may be mixed with the air from the drying hood before the mixture is applied to the respective segment of the web. Thereby, the temperature and / or the humidity of the air applied to the web may be controlled individually for each applicator portion. In some embodiments, each applicator portion is adapted to receive, in addition to the respective portion of the air from the drying hood, additional air as well as steam, wherein the flows of the additional air and the steam to each applicator portion are individually adjustable. Thereby, an additional air conduit as well as a steam conduit may guide a selected flow of additional air or steam to the air from the drying hood. The drying in each width segment may be controlled by adding variable amounts of additional air or steam.

[0023] By varying the flow of additional air and / or the flow of steam, the dryness after the drying cylinder can be modified and the cross directional variation could be reduced, which improves the control of the moisture humidity at reel, which as suggested above reduces the need to over-dry the paper, whereby the overall energy consumption may be reduced and / or the saved energy may be used to boost production.

[0024] For example, by allowing additional air to enter one of more of the applicator portions, it is possible to lower the paper dryness at the corresponding paper tissue web segments. By allowing steam to enter one of more of the applicator portions, it is possible to increase the paper dryness at the corresponding paper tissue web segments. Preferably, steam and additional air are not allowed at the same time into a single applicator portion. Nevertheless, it is possible to allow steam into one or more of the applicator portions, and simultaneously additional air into one or more of the remaining applicator portions. Also, an applicator portion into which steam is allowed, and an applicator portion into which additional air is allowed, may be close, or even adjacent, to each other.

[0025] In some embodiments, each applicator portion is adapted to receive, in addition to the respective portion of the air from the drying hood, atomized water, wherein the flow of the atomized water to each applicator portion is individually adjustable. The atomized water can be produced in any suitable way. For example, air may be mixed with water to create fine droplets or a fog, and / or pressurized water may be applied to nozzles distributed across the web.

[0026] The object is also reached with a drying system adapted to form a part of a machine for producing a paper tissue web, - wherein the system is adapted to guide air from a heat source to an applicator comprised in the system and adapted to apply the air to the paper tissue web,

[0027] - wherein the applicator presents a plurality of applicator portions distributed across the width of the paper tissue web, each applicator portion being adapted to apply a portion of the air guided from the heat source to a width segment of the paper tissue web, wherein each applicator portion is adapted to receive, in addition to the respective portion of the air from the heat source, steam and / or additional air, wherein the flow of the steam to each applicator portion is individually adjustable and / or the flow of the additional air to each applicator portion is individually adjustable.

[0028] The drying system may comprise an application adjustment arrangement arranged to provide the steam and / or additional air to the applicator portions. Thereby, the humidity and / or the temperature of the air applied to the paper tissue web by each applicator portion may be individually adjusted.

[0029] The heat source may be a drying hood for a drying cylinder, such as a Yankee cylinder. However, alternatively, the heat source may be a heated air generator, such as a burner, an electric heater, or a steam coil. In other alternatives, the air may be process air from a part of the machine which is not the drying hood for the drying cylinder.

[0030] The object is also reached with a control system according to claim 9.

[0031] DESCRIPTION OF THE DRAWINGS

[0032] Below embodiments of the invention will be described with reference to the drawings, in which fig. 1 shows schematically a part of a machine for producing a paper tissue web, fig. 2 and fig. 3 show schematically an applicator to be used with the machine of fig.

[0033] 1, fig. 4 shows schematically an applicator in an alternative embodiment of the invention, and parts of a control system for the applicator, fig. 5 - fig. 8 show tables indicating temperatures and humidities of air applied by the applicator in fig. 4 to segments of the web, and graphs indicating web segment humidity levels, fig. 9 shows a view from below of an applicator according to a further embodiment of the invention, fig. 10 shows a side view of the applicator in fig. 9, fig. 11 shows schematically an applicator in another embodiment of the invention and fig. 12 shows schematically a part of a machine in yet another embodiment of the invention.

[0034] DETAILED DESCRIPTION OF EMBODIMENTS

[0035] Fig. 1 shows a part of a machine for making a tissue paper web W. Parts of the machine may be as described in US9702084B2 incorporated by reference. The tissue web W has first been formed in a former such as a crescent former where a fibrous stock suspension is injected by a head box into a gap between two fabrics. Since this is a well-known procedure, it will not be described further here. The newly formed tissue paper web is carried forward for pressing and drying. For example, it may be carried forward on the lower side of a felt 3 which, in many practical embodiments, may be one of the fabrics between which the tissue paper web has originally been formed.

[0036] The tissue paper web W may travel at speeds of 1500 m / min-2500 m / min or 1700 m / min- 2500 m / min and preferably 1800 m / min-2400 m / min. Embodiments are conceivable in which the web W travels at a speed of 1800 m / min-2000 m / min.

[0037] The tissue paper web W is carried by the felt and passed together with the felt 3 through an extended nip N formed between an extended nip unit 2 and a Yankee drying cylinder 1.

[0038] The extended nip unit 2 is preferably an enclosed roll having a flexible tubular jacket 18 (such as a shoe press belt) which can be made of polyurethane or a material that comprises polyurethane or has similar properties. The extended nip unit may also have a press body 17 which may be a concave shoe of metal, for example steel. The press body 17 could also be an elastically deformable body and the extended nip unit could be designed according to, for example, European patent No. 1678374. The extended nip unit could also be designed in other ways. For example, the extended nip unit 2 could be designed in the way disclosed in EP 2085513 but other known extended nip units could also be used.

[0039] As can be seen in fig. 1, the tissue paper web W is carried on the felt 3 through the extended nip N in such a way that, in the extended nip N, the tissue paper web W contacts the outer surface 4 of the Yankee drying cylinder 1. The web W is separated from the felt 3 when passing through the nip N, and transferred to the Yankee drying cylinder. The web W and the felt 3 are led over a suction roll 5 prior to the extended nip N. Thereby, the felt 3 contacts the suction roll 5, and the felt 3 is located between the tissue paper web W and the suction roll 5. The suction roll 5 is used to drain partly the water from the web W. The suction roll 5 has a suction zone 6 over which the felt 3 and the tissue paper web W pass together.

[0040] An applicator 7 is arranged opposite the suction roll 5 and partially surrounds the suction roll 5 and the applicator 7 has such an extension around the suction roll that the applicator 7 covers the entire suction zone 6. In some embodiments however, the applicator 7 covers less than the entire suction zone 6.

[0041] The applicator 7 comprises an envelope 701 divided into portion envelopes as detailed below. The applicator forms a cavity 702 adapted to receive process air, and divided into portion cavities as detailed below. The envelope 701 is adapted to extend, with an envelope main direction in web width direction which is transverse to a direction of movement of the paper tissue web W. The envelope 701 further comprises a distribution plate 703 that is provided with a plurality of orifices or distribution holes, wherein the distribution plate 703 is facing the suction roll 5.

[0042] The suction roll 5 may have a diameter of 0.50-2.00 meters, e.g. 1.20 meters. The suction zone may have an extension in the axial direction of 3.00-12.00 meters, e.g. 5.70 m. The suction zone 6 may extend for 45°-180° in the circumferential direction, e.g. 120° (a third of the total circumference of the suction roll). The total area of the suction zone may thereby be about 0.6-37.7 m2, e.g. about 7.16 m2.

[0043] Moist hot process air is fed from the applicator 7 through the plurality of distribution holes 704 and sucked through the tissue paper web and the felt 3 by the suction roll 5. During this, the tissue paper web W is directly exposed to the applicator 7 such that the moist hot air reaches the tissue paper web W without having to pass through any fabric before reaching the tissue paper web. The total air flow from the applicator 7 through the tissue paper web and into the suction roll may vary typically, depending on the width of the machine, from 0.5 to 3.0 kgDA / s, (kilograms dry air per second).

[0044] The Yankee drying cylinder 1 is covered by a drying hood 8 which is a Yankee hood which has an air heating and distribution system 9. The heating and air distribution system 9 may comprise one or several heaters 15 and conduits 16 through which hot air can be fed to the drying hood 8, i.e. the Yankee hood. This hot air is blown onto the tissue paper web and contributes to the evaporation of water from the tissue paper web.

[0045] Waste air from the Yankee hood can then be exhausted from the Yankee hood and this exhaust air (waste air) is moist and hot. Hot exhaust air is taken from the drying hood 8 and fed through a conduit 10, or main conduit 10, to the applicator 7 and used to supply the applicator 7 with the moist hot process air. An air supply fan 11 is advantageously arranged to blow the hot and moist exhaust air from the drying hood 8 to the applicator 7. To adapt the quantity of exhaust air blown to the applicator 7 to the quantity of exhaust air that is available from the drying hood 8, the speed of the air supply fan 11 may be controlled. A control device 12 may be connected to the air supply fan 11 to control the speed of the fan. The moist hot process air has a temperature in the range of 100° C.-3500C. and preferably in the range of 150° C.-3000C. The moist hot process air has a moisture content of 150 g water / kg dry air- 1000 g water / kg dry air (i.e. 150 grams of water per kilogram dry air-1000 grams of water per kilogram dry air). The pressure of the moist hot process air coming from the drying hood 8 (the Yankee hood) will normally be at about normal atmospheric pressure or slightly higher, i.e. at about 101 KPa. When the moist hot process air reaches the applicator 7, the overpressure of the moist hot process air may normally be 0.3 KPa-2 KPa but in some cases an overpressure of up to 3 KPa or even higher can be considered.

[0046] The conduit 10 can be equipped with an inlet fresh air stack with a damper, that is used to control the temperature of the moist hot air delivered to the applicator. Another way to control the temperature is by injection of a controlled amount of water or a mixture of water and compressed air or by injection of steam. Typically the air delivered to the applicator has to be in the range of 90°C-180°C. Moreover the conduit 10 is equipped with a filter used to clean the air before delivery to the applicator. The filter can be mechanical means or water means or any other effective solution.

[0047] This hot moist process air is then sucked through the tissue paper web W by the suction roll 5. When the hot moist process air is sucked through the tissue paper web W, moisture in the air condensates on the tissue paper web W and thereby raises the temperature of the tissue paper web W before the tissue paper web W passes through the extended nip N. Also, a dewatering function of the suction roll is improved by the hot moist process air. The temperature of the tissue paper web would be raised also by hot air that contained no moisture at all but condensation produces a better heating effect, even if only a part of the water in the moist hot process air condensates.

[0048] A control system for the applicator comprises a detection unit 31, e.g. a scanner, which is provided at the web, downstream of the applicator. The detection unit 31 may be provided downstream of the drying cylinder 8, for example at a reel (not shown) of the tissue machine. However, other locations are possible for the detection unit 31, such as after the extended nip unit 2. The detection unit 31 is adapted to detect, or read, the moisture of segments of the web W, which segments are distributed in the cross-machine direction of the web. The control device 12 is adapted to receive from the detection unit 31 signals indicative of web segment moisture levels.

[0049] The control device 12 may be a computer, a processing device, an automation control unit etc. The control device 12 may comprise a processing module, a memory. The memory may comprise instructions, e.g. in the form of a computer program. The control device 12 may further comprise a receiving module and a sending module. The receiving module may receive commands and / or information from various devices, and the sending module may send commands and / or information to various devices.

[0050] Reference is made also to fig. 2. The applicator 7 presents a plurality of applicator portions 7a, 7b, 7c, three of which are shown in fig. 2, distributed across the width of the web. Each applicator portion 7a, 7b, 7c is adapted to apply a portion of the air guided from the drying hood to a width segment of the web. An application adjustment arrangement 110 is arranged to individually adjust the flow of the air applied to the web by each applicator portion 7a, 7b, 7c. For this, the system 100 is adapted to guide the air to the applicator portions 7a, 7b, 7c via respective portion conduits 120 (or 120a, 120b, 120c). The portion conduits 120 may branch from a main conduit 10. As detailed further below, each applicator portion 7a, 7b, 7c may be adapted to receive additional air via a respective air conduit 130 (or 130a-d), and steam via a respective steam conduit 160 (or 160a-d).

[0051] The applicator 7 further comprises, for each applicator portion 7a, 7b, 7c, a portion envelope 701a, 701b, 701c forming a portion cavity 702a, 702b, 702c. The portion envelopes 701a, 701b, 701c may be separated by separation walls 705a (two shown in fig. 2). Each portion conduit 120 leads into a respective of the portion envelopes 701a, 701b, 701c. Each portion envelope 701a, 701b, 701c comprises a portion distribution plate 703 (or 703a, 703b, 703c) presenting a plurality of distribution holes (704) to distribute the air across the respective width segment of the web. Alternatively, there may be one single distribution plate 703 covering all portion envelopes 701a, 701b, 701c.

[0052] Reference is made to fig. 3 showing the applicator 7 with four of its applicator portions 7a, 7b, 7c, 7d. The portion conduits 120 are not shown in fig. 3.

[0053] In addition, the hot and humid air coming from the drying hood, each applicator portion 7a, 7b, 7c, 7d is adapted to receive additional air. The air may be fresh air. The flow of the additional air to each applicator portion 7a, 7b, 7c, 7d may be individually adjustable. For example, for each applicator portion an air conduit 130 (or 130a-d) may be provided. Each air conduit 130 may be provided with a valve 140 (140a-d) to control the flow in the respective air conduit 130. Thereby, the temperature and humidity of the air applied to the web by each applicator portion 7a, 7b, 7c, 7d can be individually adjusted. In some detail, the moist hot process air from the drying hood 8 may be selectively mixed with fresh air to reduce the temperature and humidity. The additional air may be provided by a schematically indicated air mover 150, such as a fan or a compressor.

[0054] Also, each applicator portion 7a, 7b, 7c, 7d may be adapted to receive steam. The flow of the steam to each applicator portion 7a, 7b, 7c, 7d may be individually adjustable. For example, for each applicator portion 7a, 7b, 7c, 7d a steam conduit 160 (or 160a-d) may be provided. Each steam conduit may be provided with a steam valve 170 (or 170a-d) to control the flow in the respective steam conduit 160. Thereby, the humidity of the air applied to the web by each applicator portion 7a, 7b, 7c, 7d can be individually adjusted. In some detail, the moist hot process air from the drying hood 8 may be selectively mixed with steam to increase the temperature and humidity. The steam may be provided by a schematically indicated steam generator 180 such as a boiler. Alternatively, the steam may be provided by a waste heat steam generator, or similar. In some embodiments, where the drying cylinder is a steam heated Yankee cylinder, a condensate tank for the Yankee cylinder may provide the steam for the applicator, e.g. by flashing to low pressure steam.

[0055] In the example in fig. 3, the air conduits 130a-d and the steam conduits 160a-d extend separately to the applicator 7. However, in some embodiments, each of the air conduits 130a- d merges with a respective of the steam conduits 160a-d before the applicator 7 is reached. Thereby, the drying system may be simplified. In such embodiments, either air or steam is provided at any given point in time.

[0056] It should be noted that, while in the example in fig. 3 there is a separation wall 705a-d between each pair of a single of the air conduits 130a-d and a single of the steam conduits 160a-d, in other embodiments, there may be no, or only partial walls separating each of such pairs of air conduits 130a-d and steam conduits 160a-d. In some embodiments, there may be a number of portion conduits provided to distribute air evenly, but another number of pairs of air conduits 130a-d and steam conduits. In some embodiments, where each applicator portion is adapted to receive steam and / or additional air, there may be no portion conduits 120 for the air coming from the drying hood. Instead, the air coming from the drying hood may be provided all the way to the applicator with a single conduit.

[0057] Reference is made to fig. 4 showing an applicator similar to the one in fig. 3, but differing in that each of the air conduits 130 merges with a respective of the steam conduits 160 before the applicator 7 is reached.

[0058] The control device 12 is adapted to individually control each of the air valves 140, and each of the steam valves 170. This control is done based on the signals from the detection unit 31, indicative of moisture levels of the web segments. Reference is made also to the tables in fig. 5 and fig. 6. The table in fig. 5 indicates, in the row named Box Blowing T, temperatures or the air applied to respective segments of the web, in degrees C, and, in the row named Box Blowing x, the humidity of the air applied to the respective segments of the web, in grams of water per kilogram of dry air. The graph in fig. 5 shows moisture percentage of the respective segments of the web, downstream of the applicator, e.g. at the reel of the machine.

[0059] The signals may indicate that the moisture level of one or more web segments is above a target level. In the example in fig. 5, the moisture levels in web segments 5, 6, and 7 are above the target level. Thereby, a moisture peak is provided. In response to this, as indicated in fig. 6, the steam valve(s) for the applicator portion(s) 702e, 702f, 702g at the web segment(s) is opened to increase the flow of steam. This will locally increase the final drying at the web segment(s). Thereby, the moisture peak may be corrected.

[0060] Reference is made also to the tables in fig. 7 and fig. 8. The signals may indicate that the moisture level of one or more web segments is below a target level. In the example in fig. 7, the moisture levels in web segments 5, 6, and 7 are below the target level. Thereby, a drying peak is provided. In response to this, as indicated in fig. 8, the air valve(s) for the applicator portion(s) 702e, 702f, 702g at the web segment(s) is opened to increase the flow of additional air. This will locally decrease the final drying at the web segment(s). Thereby, the drying peak may be corrected.

[0061] The control device 12 may be adapted to control the valves 140, 170 so as to keep the moisture level at each web segment within an interval, defined by a minimum moisture level and a maximum moisture level.

[0062] It should be noted that alternatives are possible for controlling the flows of steam and additional air. The valves 140, 170 may be of an on / off type. However, preferably, they are modulating valves. Thereby, a more precise control may be obtained. In some embodiments, the valves may be adapted to be maneuvered manually. Thereby, the web segment moisture levels may be indicated, e.g. on a screen, to an operator.

[0063] The detection unit 31 may for example be a commercially available microwave scanner. Such a scanner may work based on the ability of water contained in the web to absorb radiation with a wavelength within the microwave field. By emitting microwaves and measuring the microwaves that pass through the web, it is possible to trace the energy absorbed by the web, which increases with the degree of humidity. Thereby, the moisture content of the web segments may be measured.

[0064] Nevertheless, instead of a scanner, the detection unit 31 may be of some other type, for example a thermocamera, adapted to detect the paper temperature. From the temperature of the individual web segments, the moisture levels of the segments may be determined.

[0065] Fig. 9 shows an applicator according to a further embodiment of the invention. Similar to the applicator in fig. 4, the air conduits (not shown) merge with a respective of the steam conduits (not shown), into respective combination conduits 190, leading the a respective of the applicator portions 7a-7f. As understood from fig. 10, each combination conduit 190 extends into and terminates in the respective portion cavity 702a-702f.

[0066] Reference is made to fig. 11, showing an applicator 7 similar to the ones presented with reference to fig. 2, but with the following difference: In each portion conduit 120 a damper 112 (or 112a, 112b, 112c) is provided to control the air flow in the respective portion conduit 120. The dampers 112 are schematically shown in a closed condition in fig 2. There are also indicated individual damper actuators, which may be actuated control the dampers (see double-headed curved arrow in fig. 2).

[0067] Reference is made to fig. 12. The embodiments described with reference to fig. 1 - fig. 11 involve an applicator 7 that is positioned such that the distribution plate 703 is facing the suction roll 5, whereby the distribution plate 703 is provided with a curvature generally corresponding to the curvature of the suction roll 5. However, an applicator 7’ may be placed “upstream” or before the extended nip unit 2 of a suction press roll as seen in the feeding direction of the web, as depicted in fig. 12. In this position, the distribution plate 703’ is flat since the paper tissue web W passing the applicator 7’ here is flat.

[0068] Similarly to the applicators in the embodiments described with reference to fig. 1 - fig. 11, the applicator 7’ in fig. 12 presents a plurality of undepicted applicator portions 7’a, 7’b, 7’c distributed across the width of the web, each applicator portion being adapted to apply a portion of the air guided from the drying hood to a width segment of the web, and the drying system comprises an application adjustment arrangement arranged to individually adjust the humidity of the air applied to the web by each applicator portion.

[0069] It is to be understood that the embodiments described above and shown in the drawings are only to be regarded as non-limiting examples of the invention and that it may be modified in many ways within the scope of the patent claims.

Claims

CLAIMS1. A drying system (100) adapted to form a part of a machine for producing a paper tissue web (W), comprising a drying hood (8) for a drying cylinder (1), such as a Yankee cylinder, arranged to engage a moving paper tissue web (W), and an applicator (7),- wherein the system (100) is adapted to guide air from the drying hood to the applicator (7), which is adapted to apply the air to the web (W),- wherein the applicator (7) presents a plurality of applicator portions (7a, 7b, 7c) distributed across the width of the moving paper tissue web (W), each applicator portion (7a, 7b, 7c) being adapted to apply a portion of the air guided from the drying hood (8) to a width segment of the moving paper tissue web (W), characterized in that the drying system (100) comprises an application adjustment arrangement (110) arranged to individually adjust the humidity, and / or the temperature of the air applied to the moving paper tissue web (W) by each applicator portion (7a, 7b, 7c).

2. A drying system (100) according to claim 1, wherein the applicator (7) comprises, for each applicator portion (7a, 7b, 7c), a portion envelope (701a, 701b, 701c) forming a portion cavity (702a, 702b, 702c), wherein each portion envelope (701a, 701b, 701c) is adapted to distribute the air across the respective width segment of the moving paper tissue web.

3. A drying system (100) according to claim 2, comprising one or more distribution plates (703) that are attached to the portion cavities (702a, 702b, 702c), the distribution plates (703) comprising a plurality of distribution holes (704) arranged adjacent one another along the width segment of the moving paper tissue web (W) and a plurality of distribution holes (704) arranged adjacent one another along the length of the moving paper tissue web (W).

4. A drying system (100) according to any one of the preceding claims, wherein each applicator portion (7a, 7b, 7c) is adapted to receive, in addition to the respectiveportion of the air from the drying hood (8), additional air, wherein the flow of the additional air to each applicator portion (7a, 7b, 7c) is individually adjustable.

5. A drying system (100) according to claim 4, comprising an air mover (150) for generating the flow of additional air.

6. A drying system (100) according to any one of the preceding claims, wherein each applicator portion (7a, 7b, 7c) is adapted to receive, in addition to the respective portion of the air from the drying hood (8), steam, wherein the flow of the steam to each applicator portion (7a, 7b, 7c) is individually adjustable.

7. A drying system (100) according to claim 6, comprising a steam generator (180) for generating the flow of steam.

8. A drying system adapted to form a part of a machine for producing a paper tissue web,- wherein the system is adapted to guide air from a heat source (8) to an applicator (7) comprised in the system and adapted to apply the air to the paper tissue web,- wherein the applicator presents a plurality of applicator portions (7a, 7b, 7c) distributed across the width of the paper tissue web, each applicator portion being adapted to apply a portion of the air guided from the heat source to a width segment of the paper tissue web, characterized in that each applicator portion (7a, 7b, 7c) is adapted to receive, in addition to the respective portion of the air from the heat source (8), steam and / or additional air, wherein the flow of the steam to each applicator portion (7a, 7b, 7c) is individually adjustable and / or the flow of the additional air to each applicator portion (7a, 7b, 7c) is individually adjustable.

9. A control system for a drying system according to claim 8, comprising a detection unit (31), adapted to be positioned at the paper tissue web (W), downstream of the applicator, and adapted to detect the moisture level, and / or the temperature, of the width segments of the web, the control system further comprising a control device (12), which is adapted to receive from the detection unit (31) signals indicative of the detected web segment moisture levels and / or temperatures, wherein the control device19 is adapted to control, in dependence on the signals received from the detection unit, the flow of steam and / or additional air to each applicator portion (7a, 7b, 7c).

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