Machine for producing fibrous web

Abstract

Embodiments of the present invention relate to a machine (1) for producing a fibrous web, such as for toilet paper, for example household paper, comprising a forming section (2) and a drying section (4, 5) wherein the machine is adapted to form a combined air flow by combining exhaust air flows from the forming section (2) and the drying section (4, 5), and a combined air heat exchanger (7) adapted to direct said combined air flow, the combined air heat exchanger (7) being adapted to retransfer heat from the combined air to the air of the combined fluid to the fluid.

Description

Technical Field

[0001] The invention relates to a machine for producing a fiber web, such as for tissue, for example paper tissue. The machine may alternatively be a paper machine or a board machine. Background Art

[0002] Efforts are being made to reduce the energy consumption associated with the use of machines for producing fibrous webs for use in tissue or paper. This may involve recovering the heat generated by such machines. For example, US11118311 describes a papermaking process having the steps of forming a wet paper web on a papermaking machine, drawing a vacuum through the web by a centrifugal blower to remove water from the web, thereby generating exhaust air, and diverting at least a portion of the exhaust air by a control circuit to a hot air drying system within the papermaking process to assist in drying the web.

[0003] WO9856986A1 discloses a device for recovering heat from the exhaust gas in the vacuum system of a paper, board or pulp machine. The exhaust gas streams discharged by different vacuum fans travel as parallel flows through different heat exchanger units of a heat recovery tower so that they do not substantially mix with each other.

[0004] However, some heat recovery devices increase the complexity of the machine and thus increase the capital cost of the machine.Therefore, it is also desirable to reduce the energy consumption associated with the use of a machine for producing a fiber web while avoiding a substantial increase in the complexity of the machine. Summary of the invention

[0005] The object of the present invention is to reduce the energy consumption associated with the use of a machine for producing a fiber web, while avoiding a substantial increase in the complexity of the machine.

[0006] This object is achieved by an aspect of the invention, which relates to a machine for producing a fiber web, such as for sanitary paper, for example for tissue paper, the machine comprising a plurality of sections adapted to provide various steps of web production, the machine adapted to pass the material of the fiber web through the sections in sequence, the machine adapted to provide two or more exhaust air flows from each of the sections. The machine is adapted to form a combined air flow by combining two or more of the exhaust air flows and to direct the combined air flow to a combined air heat exchanger adapted to transfer heat from the combined air to a fluid.

[0007] For example, the machine may be adapted to provide a first exhaust air flow from a first of the sections, and a second exhaust air flow from a second of the sections, the second section being different from the first section. Thus, the machine may be adapted to form a combined air flow by combining the first exhaust air flow and the second exhaust air flow.

[0008] Each section may comprise at least one carrier for the web, for example in the form of a fabric or a cylinder.The carrier of any section is preferably different from the carrier of any other section.

[0009] The machine may include what is referred to herein as a combined air heat exchanger. By virtue of the machine being adapted to form a combined air flow by combining two or more of the exhaust air flows, and being adapted to direct the combined air flow to a combined air heat exchanger adapted to transfer heat from the combined air to a fluid, the combined air heat exchanger may be used to extract heat from two air flows originating from different sections of the machine. Thus, a single heat exchanger may be used to extract excess heat from both sections. This will help to keep the complexity of the machine, and therefore the capital cost of the machine, relatively low.

[0010] Furthermore, the present invention provides energy savings compared to known heat recovery methods. In the known process of US11118311, the exhaust air diverted into the hot air drying system will increase the air mass in the hot air drying system. This will increase the fan demand and therefore the power consumption of the system. With heat recovery according to the present invention, this increase in air mass and the attendant increase in power consumption can be avoided.

[0011] In said aspect of the invention, said plurality of sections comprises a forming section adapted to form a web according to a furnish. The forming section comprises an air moving device having an inlet and an exhaust, the air moving device being arranged to provide a pressure gradient across the web being formed in the forming section to move air through the web being formed, thereby removing water from the web being formed. Thus, said two or more exhaust air streams adapted to be combined by the machine to form a combined air stream comprise an air stream from the exhaust of the air moving device.

[0012] The forming section may include a carrier for the web. The carrier may be in the form of a permeable sheet, i.e. a mesh, such as a wire mesh. An air moving device is preferably located downstream of the web being formed, along the path of the air flow moving through the web being formed. The air moving device may be, for example, a vacuum blower. The air flow moving through the web being formed may be preheated. However, in some embodiments, the air flow is not heated before passing through the web. In any case, the air may be heated by compression in the air moving device. Thus, the air may reach, for example, 125-170°C.

[0013] In said aspect of the invention, said plurality of sections comprises a drying section adapted to subject the web formed by the forming section to a drying process in order to dry the web formed by the forming section. Thus, the two or more exhaust air streams adapted to be combined by the machine to form a combined air stream comprise an air stream having residual heat from the drying process. The air having residual heat from the drying process may be air having residual heat from the drying process. The air having residual heat from the drying process may be exhaust air from the drying process.

[0014] Thus, in said aspect of the invention, a first of the sections is a forming section and a second of the sections is a drying section. Thus, the machine is adapted to form a combined air stream by combining an air stream from the exhaust of the air moving device and an air stream having residual heat from a drying process. Thus, a combined air heat exchanger may be used to extract heat from the air moving device exhaust air stream and the air stream having residual heat from the drying process.

[0015] With the machine according to said aspect of the invention, a single heat exchanger can be used to extract excess heat from both the forming section and from the drying section. This will help to reduce the complexity of the machine, and therefore reduce the capital cost of the machine. Moreover, the mixture of air from the forming section and air from the drying section will carry the combined energy of the two air streams, and this will increase the energy available to the heat receiving fluid or fluids of the heat exchanger.

[0016] The air flow from the exhaust of the air moving device may be directed towards the combined air heat exchanger through the shaped exhaust duct. The machine is preferably arranged to direct the air flow with residual heat from the drying process through the drying exhaust duct towards the combined air heat exchanger. The shaped exhaust duct may be combined with the drying exhaust duct to form a combined air duct. The combined air duct may extend from the location where the combined air flow is formed.

[0017] In some embodiments, the drying exhaust fan is provided in the drying exhaust duct.Thus, the machine is preferably arranged to direct the air flow from the exhaust outlet of the air moving device into the drying exhaust duct downstream of the drying exhaust fan.

[0018] Alternatively, the machine is arranged to direct the air flow from the exhaust outlet of the air moving device into the dry exhaust duct upstream of the dry exhaust fan.

[0019] Preferably, the drying section includes a through air drying (TAD) section. The TAD section may include a TAD cylinder having a peripheral structure having a plurality of openings. The TAD section may also include a TAD fabric, which forms an infinite loop extending partially around the TAD cylinder through a plurality of rollers. Therefore, the TAD section may be arranged to establish a pressure difference between the outside and inside of the TAD cylinder, thereby sucking air through the web, the TAD fabric and the peripheral structure of the TAD cylinder to form a TAD exhaust airflow. Therefore, the machine is preferably arranged to guide at least a portion of the TAD exhaust in the TAD exhaust airflow to form one of the two or more exhaust airflows suitable for being combined by the machine to form a combined air flow.

[0020] The TAD section may form at least a portion of the drying section described above. Thus, in some embodiments, a first of these sections is a forming section and a second of these sections is a TAD section. Thus, the machine may be arranged to direct at least a portion of the TAD exhaust gas stream to form at least a portion of the air stream having residual heat from the drying process to combine with the air stream from the exhaust port of the air moving device. Thus, a combined air heat exchanger may be used to extract heat from the air moving device exhaust gas stream and at least some of the TAD exhaust gas stream.

[0021] The air drawn through the web, the TAD fabric and the peripheral structure of the TAD cylinder can be preheated, for example, in a TAD air system. Such a TAD air system can circulate air from the TAD cylinder to a TAD hood that at least partially surrounds the TAD cylinder. The circulation can include at least a portion of the TAD exhaust airflow. Thus, the air can be heated by a heater. Moreover, air can be added to the recirculating air. For example, the heater can be a burner supplied with added air and fuel.

[0022] In some embodiments, the drying section comprises a Yankee dryer section including a Yankee dryer. Thus, the two or more exhaust air streams suitable for the machine to combine to form the combined air stream include a Yankee hood exhaust air stream from a hood of the Yankee dryer. The Yankee hood exhaust air stream may have residual heat from the Yankee drying process.

[0023] Where the machine comprises a TAD section, the Yankee dryer section may be located downstream of the TAD section along the path of the web through the machine.

[0024] The Yankee section may form at least a portion of the drying section described above. The Yankee hood exhaust airflow may form at least a portion of a second exhaust airflow that will be combined with a first exhaust airflow from a first of the sections to form combined air that will be directed to a combining air heat exchanger. For example, the Yankee hood exhaust airflow may be combined with an air moving device exhaust airflow of a forming section to form combined air. Additionally, or alternatively, the Yankee hood exhaust airflow may be mixed with at least a portion of a TAD exhaust airflow from a TAD section.

[0025] Thus, in some embodiments, the Yankee hood exhaust airflow, at least a portion of the TAD exhaust airflow, and the air moving device exhaust airflow from the forming section can be combined and directed to a combined air heat exchanger. Thus, the Yankee hood exhaust airflow can be combined with at least a portion of the TAD exhaust airflow before the combined TAD exhaust airflow and Yankee hood exhaust airflow are combined with the air moving device exhaust airflow.

[0026] In some embodiments, the Yankee air system circulates air from the hood of the Yankee dryer, is heated via a Yankee circulation duct, and returns to the hood. Thus, a portion of the circulating air can be directed to form a Yankee hood exhaust airflow, which is combined with the exhaust airflow from the forming section and directed to the combined air heat exchanger. In other embodiments, the Yankee hood exhaust airflow is directed directly from the hood of the Yankee dryer.

[0027] As suggested, the Yankee hood exhaust airflow and at least a portion of the TAD exhaust airflow may be combined and directed to a combined air heat exchanger. In such an embodiment, there may or may not be an air moving device exhaust airflow directed to the combined air heat exchanger.

[0028] Thus, a first of the sections may be a TAD section. Thus, the machine may be arranged to direct at least a portion of the TAD exhaust airflow to form at least a portion of the first exhaust airflow as an air flow with residual heat. Thus, a second of the sections may be a Yankee dryer section, wherein the machine is arranged to form at least a portion of the second exhaust airflow by a Yankee hood exhaust airflow from a hood of the Yankee dryer.

[0029] Where the two or more exhaust air streams that the machine is adapted to combine include a Yankee hood exhaust air stream, preferably the machine is arranged to direct air in the Yankee hood exhaust air stream to the Yankee heat exchanger and to direct air from the Yankee heat exchanger in the Yankee hood exhaust air stream to form part of the combined air stream. In some embodiments, the machine is adapted such that upstream of the Yankee heat exchanger, the Yankee hood exhaust air stream is combined with an air moving device exhaust air stream from the forming section.

[0030] The combined air heat exchanger may be an air to liquid heat exchanger. The liquid to which the combined air heat exchanger transfers heat may be water, glycol, or a mixture of two or more liquids, such as water and glycol. Alternatively, the combined air heat exchanger is an air to air heat exchanger. Therefore, the fluid to which the combined air heat exchanger transfers heat may be air.

[0031] In some embodiments, the machine is arranged to deliver a fluid to a heating system separate from the machine, to which fluid the heat from the combined air stream has been transferred. Thus, the heating system may be a water heating system, for example for process water, white water or fresh water, or for building heating or ceiling heating. Alternatively, the machine is arranged to deliver a fluid to a part of the machine, to which fluid the heat from the combined air stream has been transferred. Thus, the heat from the combined air heat exchanger may be used in the machine itself.

[0032] In some embodiments, the combined air heat exchanger is a first heat exchanger and the fluid is a first fluid, wherein the machine includes a second heat exchanger arranged in parallel with the first heat exchanger and adapted to receive at least a portion of the combined air flow and adapted to transfer heat from the combined air to the second fluid. The forming exhaust duct derived from the forming section can be combined with the drying exhaust duct derived from the drying section to form a combined air duct. The combined air duct can be arranged to guide the combined air from the location where the combined air flow is formed. The combined air duct can be arranged to guide the combined air to the first heat exchanger. A branch duct can be provided to guide at least a portion of the combined air to the second heat exchanger.

[0033] Preferably, the machine is suitable for selectively directing the combined air flow to the first heat exchanger or the second heat exchanger. The selectivity can be provided by one or more dampers. Therefore, by properly controlling the one or more dampers, the combined air flow can be divided into two or more sub-airflows, each of which is directed to a respective heat exchanger, including the first heat exchanger and the second heat exchanger. Moreover, by properly controlling one or more dampers, the combined air flow can be directed to one or more heat exchangers, but less than all heat exchangers. Each heat exchanger can be suitable for transferring heat to a respective heat receiving fluid, such as water. The fluid can form multiple parts of various heating systems for various purposes in and / or separated from the machine. Multiple parallel heat exchangers arranged to selectively receive the combined air provide flexibility for the use of heat in the combined air. In addition, the heat exchangers can be optimized for the individual process heating requirements of the various systems they serve. At the same time, combining the air flows from the drying section and the forming section allows an increase in the total available energy and allows an optimized design of the heat exchanger combination including the first heat exchanger and the second heat exchanger. Thus, good control of heat transfer to multiple heat absorbing streams, for example in a single heat exchanger column, can be provided.In particular, if the heat receiving fluid is water or water-based, routing and control including bypasses becomes easy to implement in practice.

[0034] Preferably, where the machine comprises a combined air duct, the combined air duct is arranged to guide the combined air from the location where the combined air flow is formed to the combined air heat exchanger, the length of the combined air duct along the path of the combined air being at least 1.0 times the hydraulic diameter of the combined air duct or the portion of the combined air duct having the smallest cross-sectional area, preferably at least 1.5 times the hydraulic diameter, for example at least 2.0 times the hydraulic diameter. It will be appreciated that the location where the combined air flow is formed is upstream of the combined air heat exchanger. In some embodiments, the combined air duct has a constant cross-sectional area, and in other embodiments the cross-sectional area of ​​the combined air duct varies along its path, for example in the presence of branch lines leading from the combined air duct.

[0035] Therefore, the extension or path of the combined air duct from the location where the combined air flow is formed to the combined air heat exchanger is at least 1.0 times the hydraulic diameter of the combined air duct or the portion of the combined air duct having the smallest cross-sectional area, preferably at least 1.5 times the hydraulic diameter, for example at least 2.0 times the hydraulic diameter. The hydraulic diameter, also called the hydraulic duct diameter, or the hydraulic pipe diameter, can be calculated using the equation dh=4A / p, where dh=hydraulic diameter (m, ft), A=cross-sectional area of ​​the duct or pipe (m2, ft2), and p=wetted circumference of the duct or pipe (m, ft). Therefore, the combined air duct can be long enough to allow the air flows from the separated parts of the machine to mix before reaching the heat exchanger. However, in some embodiments, a mixing enhancement device can be provided in the combined air duct.

[0036] Preferably, no heat exchanger is provided in the combining air duct, which is arranged to guide the combined air from the location where the combined air flow is formed to the combining air heat exchanger. Thus, it can be ensured that any heat exchange is only provided when the air flows from different machine sections are mixed.

[0037] Other aspects of the invention provide a machine according to claims 14 and 15. The advantages of such a machine can be understood from the above discussion. In such a machine, the air flows from the forming section and the drying section of the machine can be combined and directed to the combined air heat exchanger. Alternatively, air flows only from different locations of the forming section of the machine can be combined. In other alternatives, air flows only from different parts of the drying section of the machine can be combined. The machine according to claims 14 and 15 may include the features of any embodiment of any aspect of the invention.

[0038] Aspects of the present invention also provide a combined air heat exchanger according to claim 16. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the present invention will be described below with reference to the accompanying drawings, in which:

[0040] Figure 1 A machine for producing a fiber web is schematically shown.

[0041] Figure 2 Shows Figure 1 part of the machine,

[0042] Figure 3 shows a part of a machine for producing a fiber web according to an alternative embodiment of the invention,

[0043] Figure 4 shows a part of a machine for producing a fiber web according to another embodiment of the invention,

[0044] Figure 5 shows a part of a machine for producing a fiber web according to another embodiment of the invention,

[0045] Figure 6 shows a portion of a machine according to a further embodiment of the invention, and

[0046] Figure 7 A part of a machine for producing a fiber web according to another embodiment of the invention is shown. DETAILED DESCRIPTION

[0047] Figure 1 A machine 1 for producing a fiber web is shown. The fiber web produced by the machine may for example be used for tissue paper, such as cloth or towels.

[0048] The machine comprises a plurality of sections 2, 4, 5 adapted to provide the various steps of web production. The machine is adapted to pass the material of the fibrous web 3 sequentially through the sections. As exemplified below, each section comprises at least one carrier 206, 402, 501 for the web 3, e.g. in the form of a fabric. The carrier of any section is preferably different from the carrier of any other part.

[0049] The machine comprises a forming section 2 adapted to form a web 3 according to a furnish. A first forming fabric 204 and a second forming fabric 206 partially surround a forming roll 208. The furnish is introduced through a headbox 202. The furnish is introduced between the first forming fabric 204 and the second forming fabric 206. After passing the forming roll 208, the first forming fabric 204 and the second forming fabric 206 are separated. The second forming fabric 206 and the web 3 pass through a dewatering zone 212, as described below. Thus, the second forming fabric 206 forms a carrier for the web 3 in the forming section 2.

[0050] The machine also includes a through air drying section 4. Through air drying is usually abbreviated as TAD. The TAD section 4 includes a TAD cylinder 401. The TAD cylinder has a peripheral structure with a plurality of openings. The openings of the peripheral structure can extend in the radial direction of the TAD cylinder. The peripheral structure of the TAD cylinder can be a honeycomb design. The TAD section 4 also includes a TAD fabric 402. The TAD fabric 402 is formed into an infinite loop extending partially around the TAD cylinder 401 by a plurality of rollers.

[0051] The machine is arranged to transfer the web 3 from the forming section 2 to the TAD fabric 402. More specifically, the machine is arranged to transfer the web 3 from the second forming fabric 206 to the TAD fabric 402. Thereby, the web 3 is brought into contact with the TAD fabric 402. The transfer station 403 may include a shoe (not shown) that presses the TAD fabric 402 toward the second forming fabric 206. The transfer station 403 may include a suction box 403' to separate the web 3 from the second forming fabric 206. In some embodiments, the transfer station 403 includes a vacuum shoe that applies a pressure below atmospheric pressure to help transfer the web 3 to the TAD fabric 402.

[0052] The TAD fabric 402 thus forms a carrier for the web 3 in the TAD section 4 .

[0053] The TAD cylinder 401 is partially surrounded by a TAD hood 407. The machine is arranged to establish a pressure difference between the outside and the inside of the TAD cylinder 401, so that air is sucked through the web 3, the TAD fabric 402 and the surrounding structure of the TAD cylinder 401. Therefore, air is sucked into the TAD cylinder 401. The pressure difference is provided by a TAD air system, such as illustrated below. A pressure lower than atmospheric pressure is established in the TAD cylinder 401 by one or more circulation fans in the TAD air system. The air is heated before being supplied to the TAD hood 407. The air is sucked from the inside of the TAD hood 407 through the web 3, the TAD fabric 402 and the surrounding structure of the TAD cylinder 401. Therefore, the air contacts the water in the web 3, and moisture is transferred from the web to the air.

[0054] The machine further comprises a Yankee dryer section 5. The machine is arranged to transfer the web from the TAD section 4 to the Yankee dryer section 5. In the Yankee dryer section 5, the web 3 is further dried while passing around a Yankee drum 501. The Yankee drum 501 is partially surrounded by a Yankee hood 502. The web is scraped off the Yankee drum 501 by a doctor blade 503 and taken up by a reel (not shown).

[0055] The Yankee cylinder 501 thus forms a carrier for the web 3 in the Yankee dryer section 5 .

[0056] The TAD section and the Yankee dryer section 5 together form what are referred to herein as drying sections 4, 5, which are adapted to subject the web formed by the forming section 2 to a drying process, thereby drying the web formed by the forming section.

[0057] Also refer to Figure 2In the dewatering area 212 of the forming section 2, a suction box 214 and an air moving device 223 remove moisture from the web 3. The air moving device 223 has an inlet and an exhaust. The air moving device 223 may be in the form of a vacuum blower. The air moving device 223 is arranged to provide a pressure gradient across the web 3 being formed in the forming section so as to move air through the web, thereby removing water from the web. The air may be heated by being compressed by the air moving device.

[0058] The air flow from the exhaust port of the air moving device 223 forms a first exhaust air flow.

[0059] The TAD air system circulates air from inside the TAD cylinder 401 via the TAD circulation duct 421. The air from inside the TAD cylinder 401 forms the TAD exhaust airflow. Circulation is provided by a circulation fan 414 in the TAD circulation duct 421. The air is heated by a burner 411, which is fed with added air AA and a fuel FL, such as natural gas. The heated air is fed to the TAD hood 407.

[0060] The machine is arranged to direct a portion of the TAD exhaust airflow to form a second exhaust airflow. To this end, some air from the TAD cylinder 401 is directed through a drying exhaust duct, in this example the TAD exhaust duct 422. An exhaust fan 413 is provided in the TAD exhaust duct 422.

[0061] The machine is arranged to direct the air flow, ie the first exhaust air flow, from the exhaust port of the air moving device 223 through one or more shaped exhaust ducts 231 into the TAD exhaust duct 422 downstream of the drying exhaust fan 413 .

[0062] Thus, the machine is adapted to form a combined air flow by combining the first exhaust air flow and the second exhaust air flow. The machine is also adapted to direct the combined air flow to the combined air heat exchanger 7. To combine the exhaust air flows, the shaped exhaust duct 231 is combined with the dry exhaust duct 422 to form a combined air duct 701. The combined air duct 701 is arranged to direct the combined air from the position CAFL where the combined air flow is formed to the combined air heat exchanger 7. Advantageously, the length of the combined air duct is at least 2.0 times the hydraulic diameter of the combined air duct 701.

[0063] The combined air heat exchanger 7 is adapted to transfer heat from the combined air to a fluid.

[0064] The combined air heat exchanger 7 may be an air to liquid heat exchanger. Alternatively, the combined air heat exchanger 7 is an air to air heat exchanger. The machine may be arranged to deliver a fluid to which heat from the combined air flow has been transferred to a heating system 8 separate from the machine.

[0065] Reference Figure 3 , showing the reference Figure 1 and Figure 2 The embodiment described is similar to the embodiment described above, except that the machine is arranged to direct the air flow from the exhaust of the air moving device 223 into the TAD exhaust duct 422 upstream of the drying exhaust fan 413.

[0066] Reference Figure 4 , showing the reference Figure 1 and Figure 2 The described embodiment is similar to the embodiment except for the following differences:

[0067] The machine is arranged to form a Yankee hood exhaust airflow from the hood 502 of the Yankee dryer section 5. To this end, the machine comprises a Yankee exhaust duct 521 extending from the hood 502. A Yankee exhaust fan 511 is provided in the Yankee exhaust duct 521.

[0068] The machine is arranged to direct the Yankee hood exhaust gas stream to a Yankee heat exchanger 9. Thus, some of the heat in the Yankee hood exhaust gas stream can be transferred to another fluid stream, for example for heat recovery. Thus, the temperature of the Yankee hood exhaust gas stream can also be reduced.

[0069] The machine is also arranged to direct the Yankee hood exhaust gas flow from the Yankee heat exchanger 9 to form part of the second gas flow. To this end, the Yankee exhaust duct 521 extends to the TAD exhaust duct 422. Thereby, the Yankee hood exhaust gas flow is combined with the TAD exhaust gas flow.

[0070] Furthermore, the machine is adapted to form a combined air flow by combining the air moving device exhaust air flow with the combined Yankee hood exhaust air flow and the TAD exhaust air flow.The machine is further adapted to direct the combined air flow to a combined air heat exchanger 7.

[0071] Reference Figure 5 , shows another embodiment, which is similar to Figure 4 Embodiment shown: The machine is adapted to direct the exhaust of the air moving device 223 to combine with the Yankee hood exhaust airflow. The air moving device exhaust is combined with the Yankee hood exhaust airflow upstream of the Yankee heat exchanger 9. In addition, the air moving device exhaust is combined with the Yankee hood exhaust airflow upstream of the Yankee exhaust fan 511.

[0072] Reference Figure 6, shows a part of a machine according to another embodiment of the present invention. The first heat exchanger, the second heat exchanger, and the third heat exchanger 7, 71, 72 are arranged in parallel with each other. The forming exhaust duct 231 derived from the forming section (not shown) is joined with the drying exhaust duct 422 derived from the drying section (not shown) to form a combined air duct 701. The combined air duct 701 is arranged to guide the combined air from the position CAFL where the combined air flow is formed to the first heat exchanger 7. Branch ducts 721, 722 are arranged to guide at least part of the combined air to the second heat exchanger 71 and the third heat exchanger 72. Branch line 720 connects the combined air duct 701 with branch ducts 721, 722. Each heat exchanger is suitable for transferring heat to a respective heat receiving fluid 80, 81, 82, such as water.

[0073] The machine is adapted to selectively direct the combined air flow to the first heat exchanger 7 or the second heat exchanger 71, 72. This selectivity is provided by dampers 711 in the combined air duct 701 and the branch ducts 721, 722. Thus, by appropriately controlling the dampers, the combined air flow can be selectively directed to one or more heat exchangers. There is also a bypass duct 723 with a bypass damper 712 for bypassing the heat exchanger with the combined air. A branch line 720 connects the combined air duct 701 with the bypass duct 723.

[0074] The combined air duct 701 may have a smaller cross-sectional area downstream of the branch line 720 than upstream of the branch line 720. Preferably, the length of the combined air duct 701 is at least 2.0 times the hydraulic diameter of the combined air duct downstream of the branch line 720.

[0075] From the above description, we can understand Figure 6 Advantages of the illustrated embodiment.

[0076] Reference Figure 7 , which shows a part of a machine according to another embodiment of the invention. As in the embodiment described above, the machine comprises a forming section 2, and the air flow from the exhaust port of the air moving device 223 of the forming section forms a first exhaust air flow.

[0077] The machine also comprises a Yankee dryer section 5 . Figure 7The machine in does not include a TAD section. The machine comprises a transfer fabric 531 to transfer the web 3 from the forming section 2 to the Yankee dryer section 5. The transfer fabric forms an endless loop through a plurality of rollers. The machine is arranged to transfer the web 3 from the second forming fabric 206 to the transfer fabric 531 and from the transfer fabric 531 to the Yankee dryer section 5. In the Yankee dryer section 5, the web 3 passes around the Yankee cylinder 501 partially surrounded by the Yankee hood 502 before the web 3 is scraped off from the Yankee cylinder 501 by the doctor blade 503 and taken up by the reel (not shown).

[0078] The Yankee air system circulates the air from the Yankee hood 502 via the Yankee circulation duct 532. The air from the Yankee hood 502 forms the Yankee circulation air. The circulation is provided by a circulation fan 533 in the Yankee circulation duct 421. The air is heated by a burner 534, which is fed by added air AA and fuel FL. The heated air is supplied to the Yankee hood 502.

[0079] The machine is arranged to direct a portion of the Yankee cycle air to form a second exhaust airflow. To this end, a portion of the air from the Yankee hood 502 is directed through a drying exhaust duct, in this example a Yankee exhaust duct 521. A Yankee exhaust fan 511 is provided in the Yankee exhaust duct 521.

[0080] The machine is arranged to direct the air flow from the exhaust port of the air moving device 223, i.e. the first exhaust air flow, into the Yankee exhaust duct 521 through one or more shaped exhaust ducts 231. In this embodiment, the first exhaust air flow is directed into the Yankee exhaust duct 521 downstream of the Yankee exhaust fan 511. Thus, the first exhaust air flow and the second exhaust air flow are combined at the combined air forming position CAFL. The machine is also adapted to direct the combined air flow to the combining air heat exchanger 7.

Claims

1. A machine (1) for producing a fiber web, such as for toilet paper, for example tissue paper, the machine comprising a plurality of sections (2, 4, 5) adapted to provide the various steps of web production, the machine being adapted to pass material of the fiber web (3) through the sections in sequence, the machine being adapted to provide two or more exhaust air flows from each of the sections, characterised in that The machine is adapted to form a combined air flow by combining two or more of the exhaust air flows and to direct the combined air flow to a combined air heat exchanger (7), the combined air heat exchanger (7) being adapted to transfer heat from the combined air to a fluid, wherein the plurality of sections (2, 4, 5) comprises a forming section (2), the forming section (2) being adapted to form the web (3) according to a recipe, the forming section comprising an air moving device (223) having an inlet and an exhaust port, the air moving device (223) being arranged to provide a pressure gradient across the web formed in the forming section to move air through the web being formed so as to remove water from the web being formed, wherein the two or more exhaust air flows adapted to be combined by the machine to form the combined air flow include an air flow from the exhaust port of the air moving device, wherein the plurality of sections (2, 4, 5) comprises a drying section (4, 5) adapted to subject a web formed by the forming section (2) to a drying process, thereby drying the web formed by the forming section, wherein the two or more exhaust air flows adapted to be combined by the machine to form the combined air flow comprise an air flow having residual heat from the drying process.

2. The machine according to claim 1, wherein: The machine is arranged to guide the air flow having residual heat from the drying process to the combined air heat exchanger (7) through a drying exhaust duct (422), wherein a drying exhaust fan (413) is disposed in the drying exhaust duct (422), wherein the machine is arranged to guide the air flow from the exhaust port of the air moving device (223) to the drying exhaust duct (422) downstream of the drying exhaust fan (413).

3. The machine according to claim 1, wherein: The machine is arranged to guide the air flow having residual heat from the drying process to the combined air heat exchanger (7) through a drying exhaust duct (422), wherein a drying exhaust fan (413) is disposed in the drying exhaust duct (422), wherein the machine is arranged to guide the air flow from the exhaust port of the air moving device (223) to the drying exhaust duct (422) upstream of the drying exhaust fan (413).

4. A machine according to any one of the preceding claims, wherein: The drying section comprises a through air drying (TAD) section (4), the TAD section (4) comprising a TAD cylinder (401) having a peripheral structure with a plurality of openings, wherein the TAD section further comprises a TAD fabric (402), the TAD fabric (402) being formed by a plurality of rollers into an infinite loop extending partially around the TAD cylinder (401), wherein the TAD section (4) is arranged to establish a pressure difference between the outside and the inside of the TAD cylinder (401) so as to draw air through the web (3), the TAD fabric (402) and the peripheral structure of the TAD cylinder (401) to form a TAD exhaust airflow, wherein the machine is arranged to direct at least a portion of the TAD exhaust airflow to form one of the two or more exhaust airflows suitable for being combined by the machine to form the combined air flow.

5. A machine according to any one of the preceding claims, wherein: The drying section comprises a Yankee dryer section (5), the Yankee dryer section (5) comprising Yankee dryers (501, 502), wherein the two or more exhaust air streams adapted to be combined by the machines to form the combined air stream comprise a Yankee hood exhaust air stream from a hood (502) of the Yankee dryer.

6. The machine according to claim 5, wherein: The machine is arranged to direct air in the Yankee hood discharge airflow to a Yankee heat exchanger (9) and is arranged to direct air in the Yankee hood discharge airflow from the Yankee heat exchanger to form part of the combined airflow.

7. A machine according to any one of the preceding claims, wherein: The combined air heat exchanger (7) is an air to liquid heat exchanger.

8. The machine according to any one of claims 1 to 6, wherein: The combined air heat exchanger (7) is an air to air heat exchanger.

9. A machine according to any one of the preceding claims, wherein: The machine is arranged to deliver a fluid to which heat from the combined air flow has been transferred to a heating system (8) separate from the machine.

10. A machine according to any one of the preceding claims, wherein: The combined air heat exchanger (7) is a first heat exchanger and the fluid is a first fluid, wherein the machine comprises a second heat exchanger (72, 73) arranged in parallel with the first heat exchanger and adapted to receive at least a portion of the combined air flow and to transfer heat from the combined air to a second fluid.

11. The machine according to claim 10, wherein: The machine is adapted to selectively direct the combined air flow to the first heat exchanger (7) or the second heat exchanger (72, 73).

12. A machine according to any one of the preceding claims, wherein: The machine comprises a combined air duct (701), which is arranged to guide the combined air from the location (CAFL) where the combined air flow is formed to the combined air heat exchanger (7), wherein the length of the combined air duct is at least 1.0 times the hydraulic diameter of the combined air duct or the part of the combined air duct having the smallest cross-sectional area, preferably at least 1.5 times the hydraulic diameter, for example at least 2.0 times the hydraulic diameter.

13. A machine according to any one of the preceding claims, wherein: No heat exchanger is provided in the combined air duct (701), which is arranged to guide the combined air from the location (CAFL) where the combined air flow is formed to the combined air heat exchanger (7).

14. A machine (1) for producing a fiber web, such as for sanitary paper, for example tissue paper, the machine comprising a plurality of sections (2, 4, 5) adapted to provide the various steps of web production, the machine being adapted to pass material of the fiber web (3) through the sections in sequence, the machine being adapted to provide two or more exhaust air flows from each of the sections, characterised in that The machine is suitable for forming a combined air flow by combining two or more exhaust air flows in the exhaust air flow, and is suitable for guiding the combined air flow to a combined air heat exchanger (7), and the combined air heat exchanger (7) is suitable for transferring heat from the combined air to a fluid, wherein the machine includes a combined air duct (701), and the combined air duct (701) is arranged to guide the combined air from the position (CAFL) where the combined air flow is formed to the combined air heat exchanger (7), wherein the extended part of the combined air duct is at least 1.0 times the hydraulic diameter of the combined air duct or the part of the combined air duct having the smallest cross-sectional area, preferably at least 1.5 times the hydraulic diameter, for example at least 2.0 times the hydraulic diameter.

15. A machine (1) for producing a fiber web, such as for sanitary paper, for example tissue paper, comprising a plurality of sections (2, 4, 5) adapted to provide the various steps of web production, the machine being adapted to pass material of the fiber web (3) through the sections in sequence, the machine being adapted to provide two or more exhaust air flows from each of the sections, characterised in that The machine is suitable for forming a combined air flow by combining two or more exhaust air flows in the exhaust air flow, and is suitable for guiding the combined air flow to a combined air heat exchanger (7), and the combined air heat exchanger (7) is suitable for transferring heat from the combined air to a fluid, wherein no heat exchanger is provided in a combined air duct (701), and the combined air duct (701) is arranged to guide the combined air from a position (CAFL) where the combined air flow is formed to the combined air heat exchanger (7).

16. A combined air heat exchanger (7) for a machine according to any one of the preceding claims, wherein: The combined air heat exchanger (7) is adapted to receive the combined air flow and to transfer heat from the combined air to a fluid.

Images