WO2025214747A1 - Method for modifying a tissue paper machine, and method for operating such a machine - Google Patents

Method for modifying a tissue paper machine, and method for operating such a machine

Info

Publication number
WO2025214747A1
WO2025214747A1 PCT/EP2025/057966 EP2025057966W WO2025214747A1 WO 2025214747 A1 WO2025214747 A1 WO 2025214747A1 EP 2025057966 W EP2025057966 W EP 2025057966W WO 2025214747 A1 WO2025214747 A1 WO 2025214747A1
Authority
WO
WIPO (PCT)
Prior art keywords
air dryer
tissue paper
paper machine
fabric
operational mode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/EP2025/057966
Other languages
French (fr)
Inventor
Bruno Tremblay
Kimberly DOWNING
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Valmet Technologies Oy
Valmet AB
Original Assignee
Valmet Oy
Valmet AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Valmet Oy, Valmet AB filed Critical Valmet Oy
Publication of WO2025214747A1 publication Critical patent/WO2025214747A1/en
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F5/00—Dryer section of machines for making continuous webs of paper
    • D21F5/18—Drying webs by hot air
    • D21F5/182—Drying webs by hot air through perforated cylinders
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F5/00—Dryer section of machines for making continuous webs of paper
    • D21F5/02—Drying on cylinders
    • D21F5/04—Drying on cylinders on two or more drying cylinders
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F5/00—Dryer section of machines for making continuous webs of paper
    • D21F5/20—Waste heat recovery
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F9/00—Complete machines for making continuous webs of paper

Definitions

  • the present invention relates to the field of tissue paper machines, and in particular to operating a tissue paper machine for manufacturing tissue paper of different grades.
  • tissue paper machine When manufacturing tissue paper, a tissue paper machine is used to form a paper web and to dry the web until a finished tissue paper is produced. Controlling the drying as the web is transported through the tissue paper machine is essential to achieve a desired end product and for achieving a good runnability of the process. Inefficient drying would cause excessive energy consumption during the last drying stage (typically a Yankee dryer) but excessive drying in the earlier drying stages (typically a through-air dryer stage, TAD) risk damage or tearing of the web when it is transferred to the Yankee.
  • TAD through-air dryer stage
  • tissue paper machine is often used for manufacturing tissue paper of different grades, ranging from tissue paper with a higher tensile strength such as towel to tissue paper with very low tensile strength such as bathroom tissue or facial tissue.
  • tissue paper with a higher tensile strength such as towel
  • tissue paper with very low tensile strength such as bathroom tissue or facial tissue.
  • the drying capacity of the tissue paper machine is adjusted so that the higher grade tissue can be produced, but that the machine must be operated at a lower speed and with reduced heating to avoid excessive drying and making the operation more difficult.
  • this leads to higher specific energy consumption.
  • the object of the present invention is to eliminate or at least to minimize the problems discussed above. This is achieved by a method for modifying a tissue paper machine and by a method for operating a modified tissue paper machine according to the appended independent claims.
  • the tissue paper machine further comprises a first fabric wrapped about a portion of a circumference of the first through-air dryer and the second through-air dryer, and also comprises a plurality of lead rolls positioned relative to each through-air dryer for directing the first fabric onto and from each through-air dryer.
  • the method for modifying the tissue paper machine comprises removing the first fabric from the tissue paper machine and mounting a second fabric wrapped about a portion of the circumference of the first through-air dryer and on at least some of the lead rolls for directing the second fabric onto and from the first through-air dryer but not the second through-air dryer.
  • one of the lead rolls of the tissue paper machine is an ingoing lead roll of the second through-air dryer, and the method comprises removing said ingoing lead roll.
  • the method comprises removing said ingoing lead roll.
  • friction against the second fabric is reduced so that wear and unintended heat generation at the lead roll is avoided.
  • the ingoing lead roll can be removed after mounting the second fabric, but mounting is facilitated where the ingoing lead roll is removed before mounting the second fabric.
  • the tissue paper machine suitably comprises a control unit comprising processing circuitry configured to operate the tissue paper machine in a first operational mode.
  • the method suitably comprises changing the first operational mode to a second operational mode, wherein said first operational mode corresponds to a first configuration of the tissue paper machine comprising the first fabric and said second operational mode corresponds to a second configuration of the tissue paper machine comprising the second fabric.
  • operation of the tissue paper machine can be changed to accommodate the change of using only the first through-air dryer for drying the paper web in the second configuration, as opposed to using both through- air dryers in the first configuration.
  • energy and cost savings can be achieved since some components can operate at reduced capacity or even be turned off completely in the second operational mode.
  • the invention also comprises a method of operating a modified tissue paper machine, where said operating method comprises modifying a tissue paper machine according to any embodiment of the invention, and operating, by processing circuitry comprised in a control unit, the modified tissue paper machine at a second operational mode, said second operational mode comprising operating the first through-air dryer in a drying mode for drying a paper web transported on the second fabric and also operating the second through-air dryer in an idle mode.
  • the modified tissue paper machine comprises a first burner configured to supply heat inside the first through-air dryer and a second burner configured to supply heat inside the second through-air dryer
  • the method may comprise operating, by said processing circuitry, the modified tissue paper machine in the second operational mode to engage only the first burner.
  • the first burner can be used to provide heat for drying the paper web at the first through-air dryer, whereas the second burner can be left off to decrease energy consumption of the modified tissue paper machine.
  • the modified tissue paper machine may comprise a first exhaust fan and a second exhaust fan for generating a flow of air through the porous cylindrical deck of the first through-air dryer and the second through-air dryer, respectively.
  • the method suitably comprises operating, by said processing circuitry, the modified tissue paper machine in the second operational mode to operate the first exhaust fan for drying a paper web transported on the second fabric and to operate the second exhaust fan at a reduced speed for limiting accumulation of moisture in the second through- air dryer.
  • efficient drying is enabled at the first through-air drying and the risk of wear or corrosion at the second through-air dryer is decreased since accumulation of moisture is decreased.
  • the method of the invention also suitably comprises operating, by said processing circuitry, the modified tissue paper machine in the second operational mode to rotate the first through-air dryer at a drying speed and to rotate the second through-air dryer at a rest speed, said rest speed being lower than the drying speed.
  • the first through-air dryer can be used for efficient drying of the paper web and the second through-air dryer can be kept rotating at a lower speed to decrease wear or damage that could arise from holding the second through-air dryer in the same position for a longer time period. Due to the weight of the through-air dryers, it is advantageous to maintain rotation even when the second through-air dryer is not used for drying the paper web.
  • the method further comprises detecting, by a sensor, an absence of an ingoing lead roll of the second through-air dryer of the modified tissue paper machine, and operating, by the processing circuitry, the modified tissue paper machine at the second operational mode in response to the detected absence.
  • the absence of the ingoing lead roll can be used to determine that the tissue paper machine is modified and to operate the tissue paper machine in the second operational mode.
  • the detection of the absence of the ingoing lead roll can also serve as a security measure since operation in the first operational mode would be prevented when it is determined that the tissue paper machine has been modified by removing the ingoing lead roll.
  • the method suitably also comprises setting, by the processing circuitry, a desired moisture content for the first through-air dryer of the modified tissue paper machine in the second operational mode, and scanning, by a scanner, a paper web downstream of the first through-air dryer to determine an actual moisture content. Furthermore, the method suitably comprises comparing, by the processing circuitry, the actual moisture content to the desired moisture content, and determining, by the processing circuitry, a change of operation of the first through-air dryer to decrease a difference between the actual moisture content and the desired moisture content. Thereby, operation of the first through-air dryer can be adjusted to achieve the desired moisture content of the paper web.
  • tissue paper machines that use two through-air dryers normally only control operation of them together or only of the second through-air dryer to ensure a desired moisture content after the through-air dryer section as a whole.
  • the modified tissue paper machine can be operated in the second operational mode to achieve that desired moisture content for the paper web after the through-air dryer section using only the first through-air dryer.
  • scan the paper web rather than scanning the finished tissue paper, since the finished tissue paper will also be subjected to other treatment steps such as a final drying on a Yankee dryer. By thus scanning the paper web, the drying operation of the first through-air dryer can be analyzed without interference from other treatment steps.
  • the scanner can optionally or additionally be used to scan the second fabric.
  • Fig. 1 discloses a schematic view from the side of a through-air dryer section, TAD, of a paper machine before modification;
  • Fig. 2 discloses a schematic view from the side of the through-air dryer section, TAD, after modification according to a first embodiment of the invention
  • Fig. 3 discloses a schematic view from the side of the through-air dryer section, TAD, after modification according to a second embodiment of the invention
  • Fig. 4 discloses schematically components of the tissue paper machine connected to the through-air dryers, TAD, and to the processing circuitry;
  • Fig. 5 discloses steps of the method for modifying a paper machine comprising a through-air dryer section, TAD, according to the invention
  • Fig. 6 discloses steps of the method for operating the modified tissue paper machine according to the invention
  • Fig. 7 discloses optional steps of the method for operating the modified tissue paper machine according to the invention
  • Fig. 8 discloses further optional steps of the method for operating the modified tissue paper machine according to the invention.
  • Fig. 9 discloses even further optional steps of the method for operating the modified tissue paper machine according to the invention.
  • tissue paper machine 1 as such will be described to give a brief overview of the configuration and use of such a machine.
  • Machines and methods for manufacturing tissue paper are well-known within the art so they will only be mentioned briefly except where the modification and operation according to the present invention is concerned.
  • the tissue paper machine 1 that is modified and operated according to the present invention comprises all sections and components necessary for producing tissue paper, and that only a drying section 10 of the tissue paper machine 1 will be described in detail below.
  • tissue paper is manufactured in a tissue paper machine by injecting stock from a headbox into a forming nip to form a paper web, and by pressing and drying said paper web to produce a finished tissue paper.
  • the paper web is transported on a series of fabrics (e.g. forming wire, felt, structured belt) that support the paper web.
  • fabrics e.g. forming wire, felt, structured belt
  • the paper web is transferred from a fabric to a final drying step, typically a Yankee dryer, that contacts the paper web directly and removes any remaining moisture to arrive at dry tissue paper.
  • Fig. 1 discloses the drying section 10 of the tissue paper machine 1 according to a first embodiment of the invention, comprising at least a first through-air dryer 11 and a second through-air dryer 12, commonly referred to as TAD rolls.
  • the first through-air dryer 11 comprises a first rotatable cylinder 111 with a first porous cylindrical deck 112
  • the second through-air dryer 12 comprises a second rotatable cylinder 121 with a second porous cylindrical deck 122.
  • a first fabric 21 is wrapped about at least a portion of a circumference of each of the first and the second through-air dryers 11, 12 such that a paper web transported on the first fabric 21 can be exposed to hot air flowing out of the through-air dryers 11, 12 through the porous cylindrical deck 122.
  • each of the through-air dryers 11, 12 being operatively connected to a burner 51, 52 for generating heat and an exhaust fan 61, 62 for blowing air heated by the burner 51, 52 towards the porous cylindrical deck 121, 122 (see Fig. 4).
  • the drying section 10 also comprises a plurality of lead rolls 30 that are positioned relative to each through-air dryer 11, 12 so that they are able to direct the first fabric 21 onto each through-air dryer 11, 12 and from each through-air dryer 12.
  • the first through-air dryer 11 is shown with an ingoing lead roll 31 and an outgoing lead roll 32
  • the second through-air dryer 12 is also shown with an ingoing lead roll 33 and an outgoing lead roll 34.
  • the first fabric 21 moves through the drying section 10 by contacting, in turn, the ingoing lead roll 31 for the first through-air dryer 11, the first through-air dryer 11, and the outgoing lead roll 32 of the first through-air dryer 11 , and then by contacting the ingoing lead roll 33 for the second through-air dryer 12, the second through-air dryer 12, and the outgoing lead roll 34 of the second through-air dryer 12.
  • the first fabric 21 then passes to a transfer nip 90 with the Yankee dryer 91.
  • the first and second through-air dryers 11, 12 are thus in serial alignment with each other, since any point on the first fabric 21 passes the first through-air dryer 11 and proceeds to pass the second through-air dryer 12.
  • the paper web W is transported on the first fabric through the drying section 10 and is transferred onto the Yankee dryer 91 in the transfer nip 90.
  • one or more additional lead rolls 92 may be provided to guide the first fabric 21 before or after the first and second through-air dryers 11, 12, as is well known in the art.
  • the first and second through-air dryers 11, 12 are driven rolls whereas the lead rolls 30 are not driven.
  • the tissue paper machine 1 of the first embodiment also comprises a control unit 40 that comprises processing circuitry 41 that is configured to control at least one property of the tissue paper machine 1 during operation.
  • the processing circuitry 41 and the control unit 40 may form a single component or may alternatively be distributed in the tissue paper machine 1.
  • the processing circuitry 41 is operatively connected to at least one component of the tissue paper machine 1 so that signals may pass from the processing circuitry 41 to said component or from said component to the processing circuitry 41. This will be explained in more detail below with reference to Fig. 4.
  • the drying section 10 preferably also comprises a sensor 70 configured to detect and absence of the ingoing lead roll 33 of the second through-air dryer 12 and/or a scanner 80 configured to scan the paper web W to determine an actual moisture content. This will be described in detail further below.
  • the drying section 10 shown in Fig. 1 is denoted as a first configuration of the drying section 10. This is a configuration that is operated in a first operational mode using both the first through-air dryer 11 and the second through-air dryer 12 to dry the paper web W.
  • first operational mode using both the first through-air dryer 11 and the second through-air dryer 12 to dry the paper web W.
  • operating the drying section 10 of Fig. 1 in the first operational mode to use both through-air dryers 11, 12, provides suitable drying of the paper web.
  • the drying section 10 is modified according to the present invention as shown in Fig. 5.
  • Modifying the drying section 10 according to the first embodiment comprises removing 101 the first fabric 21 from the tissue paper machine 1 and mounting 102 a second fabric 22 instead. This is shown in Fig. 2, where it can be seen that the second fabric 22 is mounted wrapped about a portion of the circumference of the first through-air dryer 11 and at least some of the lead rolls 30 so that the second fabric 22 is directed onto and from the first through-air dryer 11 but so that the second fabric 22 is not wrapped about or directed onto and from the second through-air dryer 12.
  • the second through-air dryer 12 is bypassed so that only the first through-air dryer 11 is able to act on the paper web W that is transported on the second fabric 22 when the tissue paper machine 1 is in use.
  • Mounting the second fabric 22 in this way means that the second fabric 22 passes through the drying section 10 when the tissue paper machine 1 is operated by passing, in turn, the ingoing lead roll 31 of the first through-air dryer 11, the first through-air dryer 11, the outgoing lead roll 32 of the first through-air dryer 11, and the ingoing lead roll 33 of the second through-air dryer 12 followed by the outgoing lead roll 34 of the second through-air dryer 12. It then proceeds to the transfer nip 90 with the Yankee dryer 91, optionally passing at least one additional lead roll 92 on the way.
  • the tissue paper machine 1 With the second fabric 22 in place, the tissue paper machine 1 is able to operate in a second operational mode where drying of the paper web W takes place on the first through-air dryer 11 but not on the second through-air dryer 12. This can also be referred to as a second configuration of the tissue paper machine 1.
  • the main difference of the first configuration of Fig. 1 and the second configuration of Fig. 2 is the arrangement of the first fabric 21 compared to the arrangement of the second fabric 22.
  • the first and second configurations can be similar or identical.
  • Fig. 3 discloses a second embodiment of the invention in which the method for modifying the tissue paper machine 1 also comprises removing 103 the ingoing lead roll 33 of the second through-air dryer 12.
  • the ingoing lead roll 33 of the second through-air dryer 12 no longer fills a purpose since the second fabric 22 is not guided to the second through-air dryer 12.
  • the ingoing lead roll 33 may also cause increased friction against the second fabric 22.
  • the ingoing lead roll 33 of the second through-air dryer 12 may be operated as a driven roll but alternatively the ingoing lead roll 33 may instead be removed from the drying section 10 altogether. Removing the ingoing lead roll 33 may take place before or after mounting the second fabric 22.
  • the ingoing lead roll 33 is removed after the first fabric 21 is removed but before the second fabric 22 is mounted. This is beneficial in facilitating the mounting of the second fabric 22.
  • operation of the tissue paper machine 1 can be changed 104 from the first operational mode to the second operational mode (see Fig. 5).
  • the processing circuitry 41 is thus configured to operate the tissue paper machine 1 both in the first operational mode that corresponds to a first configuration where the first fabric 21 is mounted in the drying section 10 as shown above in Fig. 1 and in the second operational mode that corresponds to a second configuration where the second fabric 22 is mounted in the drying section 10 as shown above in Fig. 2 and in Fig. 3.
  • the change of operational mode typically takes place by an operator selecting the second operational mode and giving this as input to the processing circuitry via an input device 42 (see Fig. 4) but it may also take place without the operator, e.g. by detecting via sensor 70 that the ingoing lead roll 33 of the second through-air dryer 12 is absent. This will be explained in more detail below.
  • the first and second fabrics 21, 22 are preferably structured fabrics, but other kinds of fabric can also be used.
  • Fig. 4 discloses the processing circuitry 41 that may be operatively connected to various components of the tissue paper machine 1. Dashed lines in Fig. 4 show operative connections of the processing circuitry 41 that may be any connections suitable for transferring signals between the processing circuitry 41 and the components (e.g. wireless connections or connections by wire). Thus, each of the components may have a sender and/or receiver configured to transmit wireless signals, or they may alternatively be connected to the processing circuitry 41 of the control unit 40 by wires.
  • the first through-air dryer 11 is connected to a first burner 51 that is configured to supply heat to the first through-air dryer 11. This may be achieved by the first burner 51 being inside the first through-air dryer 11 , or alternatively by the first burner 51 being placed outside the first through- air dryer 11 with at least one conduit through which a heated medium (typically air) can be transferred from the first burner 51 to the first through- air dryer 11.
  • a first circulation fan 63 is connected to the first through- air dryer 11 and configured to generate an airflow through the porous deck 112. This may be achieved by the first circulation fan 63 being placed inside the first through-air dryer 11 or alternatively by the first circulation fan 63 being connected by at least one conduit to the first through-air dryer 11.
  • a first exhaust fan 61 is connected to the first through-air dryer 11 and configured to maintain a mass balance in the air system and remove combustion air from the first burner 51.
  • a second burner 52, a second circulation fan 64 and a second exhaust fan 62 are connected to the second through-air dryer 12.
  • first and second through-air dryers 11, 12 There may also be additional fans connected to each of the first and second through-air dryers 11, 12, such as a combustion fan that ensures that the first and second burners 51, 52 are supplied with oxygen.
  • a combustion fan that ensures that the first and second burners 51, 52 are supplied with oxygen.
  • One such fan may be provided to each of the first and second through-air dryers 11, 12, or alternatively one fan may be connected to both of the through-air dryers 11 ,
  • turning off the second burner 52 means that also the associated combustion fan can be turned off.
  • the processing circuitry 41 is preferably connected to each of the through-air dryers 11, 12 and each of the burners 51, 52 and exhaust fans 61, 62 and circulation fans 63, 64. Also, the processing circuitry 41 may be connected to the sensor 70 and to the scanner 80, and further to an input device 42 through which manual input from an operator can be received.
  • Fig. 5 discloses the method according to the invention of modifying the tissue paper machine 1, comprising the steps of removing 101 the first fabric 21 and mounting 102 the second fabric 22.
  • the method may also comprise the optional steps of removing 103 the ingoing lead roll 33 of the second through-air dryer 12 and of changing 104 to the second operational mode.
  • This method comprises modifying 201 the tissue paper machine 1 as shown in Fig. 5 and operating 202 the tissue paper machine 1 at the second operational mode with the first through-air dryer 11 in a drying mode and the second through-air dryer 12 in an idle mode where the second through-air dryer 12 operates at reduced capacity.
  • the drying mode comprises operating the first through-air dryer 11 to remove moisture from the paper web W transported on the second fabric 22, whereas the idle mode comprises maintaining the second through-air dryer 12 in the tissue paper machine 1 but not operating to remove moisture from the paper web W.
  • Fig. 7 discloses features of the second operational mode regarding operation of the first burner 51 and first exhaust fan 61, and optional features regarding the second burner 52 and second exhaust fan 62. It also comprises optional features of the rotational speed of the through-air dryers 11, 12.
  • the second operational mode comprises rotating the first through- air dryer 11 at a drying speed and the second through-air dryer 12 at a rest speed.
  • the drying speed of the first through-air dryer 11 is preferably lower than a rotational speed of the first through-air dryer 11 in the first operational mode. It is advantageous to lower the speed of the tissue paper machine 1 as a whole when producing tissue with lower tensile strength, to ensure that the paper web W (that is more fragile than a paper web W with a higher tensile strength) is not damaged. This slower speed in itself causes an increased drying since the paper web W has a longer contact time with the first through- air dryer 11.
  • the rest speed of the second through-air dryer 12 is preferably lower than the drying speed of the first through-air dryer 11. Even though the second through-air dryer 12 is not used to dry the paper web W, it is advantageous to maintain a rotation of the second through-air dryer 12 to avoid excessive wear on components such as roll bearings that could otherwise arise when the second through-air dryer 12 is completely still and thus exerts a static load on the roll bearings.
  • the second operational mode comprises engaging the first burner 51 but not the second burner 52.
  • engaging only the first burner 51 drying of the paper web W takes place as desired but there is a considerable energy saving since the second burner 52 is not operated.
  • the second operational mode comprises engaging both the first and the second exhaust fans 61, 62.
  • the first exhaust fan 61 is thereby operated to ensure drying of the paper web W as described above, whereas operation of the second exhaust fan 62 is advantageous in limiting accumulation of moisture in the second through-air dryer 12. This in turn is highly advantageous in minimizing corrosion.
  • drive power of the first through-air dryer 11 may also be increased to enable driving of the second fabric 22 when the second through-air dryer 12 is bypassed.
  • an additional drive roll may be added to ensure that there is sufficient drive power to maintain a desired speed in the drying section 10.
  • the second operational mode may be initiated by a human operator communicating with the processing circuitry 41 via the input device 42.
  • Fig. 8 discloses optional steps of initiating the second operational mode without input from an operator. This comprises, in optional step 206, detecting an absence of the ingoing lead roll 33 of the second through-air dryer 12 by means of the sensor 70 (see Fig. 1-3).
  • the sensor may be a proximity switch, an optical sensor or any other suitable type of sensor that is able to detect whether an object is present or not (e.g. an inductive proximity sensor).
  • the sensor may be arranged in connection with the ingoing lead roll 33 or integrated with the ingoing lead roll or may alternatively be arranged at a distance from the ingoing lead roll 33.
  • the tissue paper machine 1 is operated at the second operation mode in response to the detected absence. This ensures that the processing circuitry 41 is able to initiate the second operational mode without requiring input from an operator, and also provides the additional security that the tissue paper machine 1 is prevented from accidentally operating in the first operational mode even though the tissue paper machine 1 has been modified to fit the second fabric 22 according to the present invention. Since many operational parameters may differ between the first and second operational modes it is advantageous both from the energy efficient and cost standpoints to ensure that the correct operational mode is selected, apart from minimizing the risk of damage to the paper web W if the tissue paper machine 1 should be operated in another mode than intended (e.g. if excessive speed of the tissue paper machine 1 were to be used even though the tensile strength of the paper web W is too low) .
  • Fig. 9 discloses optional steps for operating the tissue paper machine 1 in the second operational mode to ensure that drying of the paper web W is efficient and achieves the desired dryness before the paper web W is transferred to the Yankee dryer 91.
  • This includes, in optional step 208, setting a desired moisture content for the first through-air dryer 11 in the second operational mode. This is a moisture content that the paper web W should have after having passed the first through-air dryer 11 but before being subjected to the final drying step on the Yankee dryer 91. It is advantageous if the paper web W is sufficiently dry before reaching the Yankee dryer 91 to avoid excessive energy consumption at the Yankee dryer 91, but it is also advantageous if the paper web W still holds sufficient moisture to facilitate transfer to the Yankee dryer 91 in the transfer nip 90.
  • the moisture content going to the Yankee dryer 91 may be in the range 5 - 50 %.
  • the Yankee dryer 91 is equipped with a wet-end hood, a dry-end hood, or a full hood covering both wet and dry ends a moisture content can be in the higher end of the range, whereas a lower end of the range is suitable in embodiments where the Yankee dryer 91 is not equipped with a hood.
  • the method then comprises, in optional step 209, to scan the paper web W downstream of the first through-air dryer 11 to determine an actual moisture content.
  • the scanner 80 is provided in the tissue paper machine 1 as shown in Fig. 1-3.
  • the scanner 80 may scan the paper web W immediately before the transfer nip 90 or in any other location after the first through-air dryer 11 but before transfer to the Yankee dryer 91. It is particularly advantageous to scan the paper web W before the final drying step on the Yankee dryer 91 since this ensures that an effect on the paper web W from drying performed by the first through-air dryer 11 is separated from the effect of the Yankee dryer 91.
  • the scanner 80 is configured to scan only the paper web W, but in other embodiments the scanner 80 is instead configured to scan the second fabric 22. Also, in some embodiments the scanner 80 is configured to scan both the paper web W and the second fabric 22.
  • step 210 the actual moisture content determined by the scanner is then compared to the desire moisture content, and in optional step 211 a change of operation of the first through-air dryer 11 to decrease a difference between the actual moisture content and the desired moisture content is determined. The change is then implemented in optional step 212.
  • the step of scanning 209 the paper web W may then be repeated at desired intervals or continuously, and optionally the desired moisture content may also be changed at regular intervals by automatically updating it or by receiving a manual input from the operator.
  • the steps of determining 211 and implementing a change 212 can be skipped so that operation of the first through-air dryer 11 is only changed when a large difference between what the moisture content should be and the real value is determined.
  • Implementing the change can comprise increasing or decreasing operation of the first burner 51 to in turn increase or decrease the exposure of the paper web W to heat from the first through-air dryer 11. It can also comprise increasing or decreasing operation of the first exhaust fan 61. It may also comprise increasing or decreasing the rotational speed of the first through-air dryer 11 and other properties of the first through-air dryer 11 may also be changed if desired.

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Abstract

The present invention relates to a method for modifying a tissue paper machine that comprises a drying section (10) with a first through-air dryer (11) and a second through-air dryer (12) in serial alignment with each other, each through-air dryer (11, 12) comprising a rotatable cylinder (111, 121) having a porous cylindrical deck (112, 122), and the tissue paper machine (1) further comprising a first fabric (21) wrapped about a portion of a circumference of the first through-air dryer (11) and the second through-air dryer (12), and also comprising a plurality of lead rolls (30) positioned relative to each through-air dryer (11, 12), and wherein the method comprises: - removing the first fabric (21), and - mounting a second fabric (22) for directing the second fabric (22) onto and from the first through-air dryer (11) but not the second through-air dryer (12).

Description

METHOD FOR MODIFYING A TISSUE PAPER MACHINE, AND METHOD FOR OPERATING SUCH A MACHINE
TECHNICAL FIELD
The present invention relates to the field of tissue paper machines, and in particular to operating a tissue paper machine for manufacturing tissue paper of different grades.
BACKGROUND
When manufacturing tissue paper, a tissue paper machine is used to form a paper web and to dry the web until a finished tissue paper is produced. Controlling the drying as the web is transported through the tissue paper machine is essential to achieve a desired end product and for achieving a good runnability of the process. Inefficient drying would cause excessive energy consumption during the last drying stage (typically a Yankee dryer) but excessive drying in the earlier drying stages (typically a through-air dryer stage, TAD) risk damage or tearing of the web when it is transferred to the Yankee.
At the same time, the same tissue paper machine is often used for manufacturing tissue paper of different grades, ranging from tissue paper with a higher tensile strength such as towel to tissue paper with very low tensile strength such as bathroom tissue or facial tissue. This means that the drying capacity of the tissue paper machine is adjusted so that the higher grade tissue can be produced, but that the machine must be operated at a lower speed and with reduced heating to avoid excessive drying and making the operation more difficult. In particular when producing the lower tensile grade tissue, this leads to higher specific energy consumption. There could also be generation of carbon monoxide in the machine hall due to low fire rate of the burners for the second through-air dryer
At present, there are no prior art solutions that enable energy efficient manufacture of both higher and lower grade tissue paper with the same tissue paper machine. There is therefore a need for improvements within this area. SUMMARY
The object of the present invention is to eliminate or at least to minimize the problems discussed above. This is achieved by a method for modifying a tissue paper machine and by a method for operating a modified tissue paper machine according to the appended independent claims.
The tissue paper machine that is modified and operated according to the present invention comprises a drying section with a first through-air dryer and a second through-air dryer in serial alignment with each other, each through- air dryer comprising a rotatable cylinder having a porous cylindrical deck. The tissue paper machine further comprises a first fabric wrapped about a portion of a circumference of the first through-air dryer and the second through-air dryer, and also comprises a plurality of lead rolls positioned relative to each through-air dryer for directing the first fabric onto and from each through-air dryer.
The method for modifying the tissue paper machine comprises removing the first fabric from the tissue paper machine and mounting a second fabric wrapped about a portion of the circumference of the first through-air dryer and on at least some of the lead rolls for directing the second fabric onto and from the first through-air dryer but not the second through-air dryer.
By thus replacing the first fabric with a second fabric that is mounted on the first through-air dryer but not the second through-air dryer, excessive drying of a paper web is avoided since the second through-air dryer is bypassed. This means that the risk of damage or breaking of the paper web is significantly reduced, while at the same time enabling efficient and convenient operation of the tissue paper machine both to produce higher grade tissue (using the first fabric) and lower grade tissue (using the second fabric). The present inventors have found that the energy savings of bypassing the second through-air dryer is in the range of 120 kWh/ MT which is equivalent to 4. 1 % of drying energy or 2.5 % of the total energy consumption of the tissue paper machine. Suitably, one of the lead rolls of the tissue paper machine is an ingoing lead roll of the second through-air dryer, and the method comprises removing said ingoing lead roll. Thereby, friction against the second fabric is reduced so that wear and unintended heat generation at the lead roll is avoided. The ingoing lead roll can be removed after mounting the second fabric, but mounting is facilitated where the ingoing lead roll is removed before mounting the second fabric.
The tissue paper machine suitably comprises a control unit comprising processing circuitry configured to operate the tissue paper machine in a first operational mode. The method suitably comprises changing the first operational mode to a second operational mode, wherein said first operational mode corresponds to a first configuration of the tissue paper machine comprising the first fabric and said second operational mode corresponds to a second configuration of the tissue paper machine comprising the second fabric. Thereby, operation of the tissue paper machine can be changed to accommodate the change of using only the first through-air dryer for drying the paper web in the second configuration, as opposed to using both through- air dryers in the first configuration. Thereby, energy and cost savings can be achieved since some components can operate at reduced capacity or even be turned off completely in the second operational mode.
The invention also comprises a method of operating a modified tissue paper machine, where said operating method comprises modifying a tissue paper machine according to any embodiment of the invention, and operating, by processing circuitry comprised in a control unit, the modified tissue paper machine at a second operational mode, said second operational mode comprising operating the first through-air dryer in a drying mode for drying a paper web transported on the second fabric and also operating the second through-air dryer in an idle mode. Thereby, an energy efficient and cost effective manufacture of tissue paper of lower tensile, lower speed grades is achieved, while at the same time also decreasing or even minimizing the risk of damage or breakage of the paper web. Suitably, the modified tissue paper machine comprises a first burner configured to supply heat inside the first through-air dryer and a second burner configured to supply heat inside the second through-air dryer, and the method may comprise operating, by said processing circuitry, the modified tissue paper machine in the second operational mode to engage only the first burner. Thereby, the first burner can be used to provide heat for drying the paper web at the first through-air dryer, whereas the second burner can be left off to decrease energy consumption of the modified tissue paper machine.
Also, the modified tissue paper machine may comprise a first exhaust fan and a second exhaust fan for generating a flow of air through the porous cylindrical deck of the first through-air dryer and the second through-air dryer, respectively. The method suitably comprises operating, by said processing circuitry, the modified tissue paper machine in the second operational mode to operate the first exhaust fan for drying a paper web transported on the second fabric and to operate the second exhaust fan at a reduced speed for limiting accumulation of moisture in the second through- air dryer. Thereby, efficient drying is enabled at the first through-air drying and the risk of wear or corrosion at the second through-air dryer is decreased since accumulation of moisture is decreased.
The method of the invention also suitably comprises operating, by said processing circuitry, the modified tissue paper machine in the second operational mode to rotate the first through-air dryer at a drying speed and to rotate the second through-air dryer at a rest speed, said rest speed being lower than the drying speed. Thereby, the first through-air dryer can be used for efficient drying of the paper web and the second through-air dryer can be kept rotating at a lower speed to decrease wear or damage that could arise from holding the second through-air dryer in the same position for a longer time period. Due to the weight of the through-air dryers, it is advantageous to maintain rotation even when the second through-air dryer is not used for drying the paper web. Suitably, the method further comprises detecting, by a sensor, an absence of an ingoing lead roll of the second through-air dryer of the modified tissue paper machine, and operating, by the processing circuitry, the modified tissue paper machine at the second operational mode in response to the detected absence. Thereby, in embodiments where the ingoing lead roll of the second through-air dryer is removed the absence of the ingoing lead roll can be used to determine that the tissue paper machine is modified and to operate the tissue paper machine in the second operational mode. Apart from thereby facilitating the switch to the second operational mode, the detection of the absence of the ingoing lead roll can also serve as a security measure since operation in the first operational mode would be prevented when it is determined that the tissue paper machine has been modified by removing the ingoing lead roll.
The method suitably also comprises setting, by the processing circuitry, a desired moisture content for the first through-air dryer of the modified tissue paper machine in the second operational mode, and scanning, by a scanner, a paper web downstream of the first through-air dryer to determine an actual moisture content. Furthermore, the method suitably comprises comparing, by the processing circuitry, the actual moisture content to the desired moisture content, and determining, by the processing circuitry, a change of operation of the first through-air dryer to decrease a difference between the actual moisture content and the desired moisture content. Thereby, operation of the first through-air dryer can be adjusted to achieve the desired moisture content of the paper web. This is particularly advantageous since tissue paper machines that use two through-air dryers normally only control operation of them together or only of the second through-air dryer to ensure a desired moisture content after the through-air dryer section as a whole. By introducing a desired moisture content for the first through-air dryer, the modified tissue paper machine can be operated in the second operational mode to achieve that desired moisture content for the paper web after the through-air dryer section using only the first through-air dryer. It is also particularly advantageous to scan the paper web rather than scanning the finished tissue paper, since the finished tissue paper will also be subjected to other treatment steps such as a final drying on a Yankee dryer. By thus scanning the paper web, the drying operation of the first through-air dryer can be analyzed without interference from other treatment steps. In some embodiments, the scanner can optionally or additionally be used to scan the second fabric.
Many additional benefits and advantages of the present invention will be readily understood by the skilled person in view of the detailed description below.
DRAWINGS
The invention will now be described in more detail with reference to the appended drawings, wherein
Fig. 1 discloses a schematic view from the side of a through-air dryer section, TAD, of a paper machine before modification;
Fig. 2 discloses a schematic view from the side of the through-air dryer section, TAD, after modification according to a first embodiment of the invention;
Fig. 3 discloses a schematic view from the side of the through-air dryer section, TAD, after modification according to a second embodiment of the invention;
Fig. 4 discloses schematically components of the tissue paper machine connected to the through-air dryers, TAD, and to the processing circuitry;
Fig. 5 discloses steps of the method for modifying a paper machine comprising a through-air dryer section, TAD, according to the invention;
Fig. 6 discloses steps of the method for operating the modified tissue paper machine according to the invention; Fig. 7 discloses optional steps of the method for operating the modified tissue paper machine according to the invention;
Fig. 8 discloses further optional steps of the method for operating the modified tissue paper machine according to the invention; and
Fig. 9 discloses even further optional steps of the method for operating the modified tissue paper machine according to the invention.
All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Any reference number appearing in multiple drawings refers to the same object or feature throughout the drawings, unless otherwise indicated.
DETAILED DESCRIPTION
The method for modifying a tissue paper machine 1 and the method for operating the modified tissue paper machine 1 will now be described in detail. First, the tissue paper machine 1 as such will be described to give a brief overview of the configuration and use of such a machine. Machines and methods for manufacturing tissue paper are well-known within the art so they will only be mentioned briefly except where the modification and operation according to the present invention is concerned. Furthermore, it is to be noted that the tissue paper machine 1 that is modified and operated according to the present invention comprises all sections and components necessary for producing tissue paper, and that only a drying section 10 of the tissue paper machine 1 will be described in detail below.
In general, tissue paper is manufactured in a tissue paper machine by injecting stock from a headbox into a forming nip to form a paper web, and by pressing and drying said paper web to produce a finished tissue paper. The paper web is transported on a series of fabrics (e.g. forming wire, felt, structured belt) that support the paper web. After forming, pressing and drying, the paper web is transferred from a fabric to a final drying step, typically a Yankee dryer, that contacts the paper web directly and removes any remaining moisture to arrive at dry tissue paper.
Fig. 1 discloses the drying section 10 of the tissue paper machine 1 according to a first embodiment of the invention, comprising at least a first through-air dryer 11 and a second through-air dryer 12, commonly referred to as TAD rolls. The first through-air dryer 11 comprises a first rotatable cylinder 111 with a first porous cylindrical deck 112, and the second through-air dryer 12 comprises a second rotatable cylinder 121 with a second porous cylindrical deck 122. A first fabric 21 is wrapped about at least a portion of a circumference of each of the first and the second through-air dryers 11, 12 such that a paper web transported on the first fabric 21 can be exposed to hot air flowing out of the through-air dryers 11, 12 through the porous cylindrical deck 122. This is achieved by each of the through-air dryers 11, 12 being operatively connected to a burner 51, 52 for generating heat and an exhaust fan 61, 62 for blowing air heated by the burner 51, 52 towards the porous cylindrical deck 121, 122 (see Fig. 4).
The drying section 10 also comprises a plurality of lead rolls 30 that are positioned relative to each through-air dryer 11, 12 so that they are able to direct the first fabric 21 onto each through-air dryer 11, 12 and from each through-air dryer 12. In Fig. 1, the first through-air dryer 11 is shown with an ingoing lead roll 31 and an outgoing lead roll 32, and the second through-air dryer 12 is also shown with an ingoing lead roll 33 and an outgoing lead roll 34. Thus, the first fabric 21 moves through the drying section 10 by contacting, in turn, the ingoing lead roll 31 for the first through-air dryer 11, the first through-air dryer 11, and the outgoing lead roll 32 of the first through-air dryer 11 , and then by contacting the ingoing lead roll 33 for the second through-air dryer 12, the second through-air dryer 12, and the outgoing lead roll 34 of the second through-air dryer 12. The first fabric 21 then passes to a transfer nip 90 with the Yankee dryer 91. The first and second through-air dryers 11, 12 are thus in serial alignment with each other, since any point on the first fabric 21 passes the first through-air dryer 11 and proceeds to pass the second through-air dryer 12. During operation of the tissue paper machine 1, the paper web W is transported on the first fabric through the drying section 10 and is transferred onto the Yankee dryer 91 in the transfer nip 90. Optionally, one or more additional lead rolls 92 may be provided to guide the first fabric 21 before or after the first and second through-air dryers 11, 12, as is well known in the art. Typically, the first and second through-air dryers 11, 12 are driven rolls whereas the lead rolls 30 are not driven.
The tissue paper machine 1 of the first embodiment also comprises a control unit 40 that comprises processing circuitry 41 that is configured to control at least one property of the tissue paper machine 1 during operation. The processing circuitry 41 and the control unit 40 may form a single component or may alternatively be distributed in the tissue paper machine 1. Also, the processing circuitry 41 is operatively connected to at least one component of the tissue paper machine 1 so that signals may pass from the processing circuitry 41 to said component or from said component to the processing circuitry 41. This will be explained in more detail below with reference to Fig. 4.
Furthermore, the drying section 10 preferably also comprises a sensor 70 configured to detect and absence of the ingoing lead roll 33 of the second through-air dryer 12 and/or a scanner 80 configured to scan the paper web W to determine an actual moisture content. This will be described in detail further below.
The drying section 10 shown in Fig. 1 is denoted as a first configuration of the drying section 10. This is a configuration that is operated in a first operational mode using both the first through-air dryer 11 and the second through-air dryer 12 to dry the paper web W. When producing grades with higher tensile strength such as towel, operating the drying section 10 of Fig. 1 in the first operational mode to use both through-air dryers 11, 12, provides suitable drying of the paper web.
When using the tissue paper machine 1 to produce tissue of lower tensile strength such as bathroom or facial tissue, the drying section 10 is modified according to the present invention as shown in Fig. 5. Modifying the drying section 10 according to the first embodiment comprises removing 101 the first fabric 21 from the tissue paper machine 1 and mounting 102 a second fabric 22 instead. This is shown in Fig. 2, where it can be seen that the second fabric 22 is mounted wrapped about a portion of the circumference of the first through-air dryer 11 and at least some of the lead rolls 30 so that the second fabric 22 is directed onto and from the first through-air dryer 11 but so that the second fabric 22 is not wrapped about or directed onto and from the second through-air dryer 12. In this way, the second through-air dryer 12 is bypassed so that only the first through-air dryer 11 is able to act on the paper web W that is transported on the second fabric 22 when the tissue paper machine 1 is in use.
Mounting the second fabric 22 in this way means that the second fabric 22 passes through the drying section 10 when the tissue paper machine 1 is operated by passing, in turn, the ingoing lead roll 31 of the first through-air dryer 11, the first through-air dryer 11, the outgoing lead roll 32 of the first through-air dryer 11, and the ingoing lead roll 33 of the second through-air dryer 12 followed by the outgoing lead roll 34 of the second through-air dryer 12. It then proceeds to the transfer nip 90 with the Yankee dryer 91, optionally passing at least one additional lead roll 92 on the way.
With the second fabric 22 in place, the tissue paper machine 1 is able to operate in a second operational mode where drying of the paper web W takes place on the first through-air dryer 11 but not on the second through-air dryer 12. This can also be referred to as a second configuration of the tissue paper machine 1.
Thus, the main difference of the first configuration of Fig. 1 and the second configuration of Fig. 2 is the arrangement of the first fabric 21 compared to the arrangement of the second fabric 22. In all other respects, the first and second configurations can be similar or identical.
Fig. 3 discloses a second embodiment of the invention in which the method for modifying the tissue paper machine 1 also comprises removing 103 the ingoing lead roll 33 of the second through-air dryer 12. With the second fabric 22 mounted in the drying section 10, the ingoing lead roll 33 of the second through-air dryer 12 no longer fills a purpose since the second fabric 22 is not guided to the second through-air dryer 12. The ingoing lead roll 33 may also cause increased friction against the second fabric 22. For these reasons, the ingoing lead roll 33 of the second through-air dryer 12 may be operated as a driven roll but alternatively the ingoing lead roll 33 may instead be removed from the drying section 10 altogether. Removing the ingoing lead roll 33 may take place before or after mounting the second fabric 22. In the first embodiment, the ingoing lead roll 33 is removed after the first fabric 21 is removed but before the second fabric 22 is mounted. This is beneficial in facilitating the mounting of the second fabric 22.
After the tissue paper machine 1 is modified according to the first embodiment or the second embodiment, operation of the tissue paper machine 1 can be changed 104 from the first operational mode to the second operational mode (see Fig. 5). The processing circuitry 41 is thus configured to operate the tissue paper machine 1 both in the first operational mode that corresponds to a first configuration where the first fabric 21 is mounted in the drying section 10 as shown above in Fig. 1 and in the second operational mode that corresponds to a second configuration where the second fabric 22 is mounted in the drying section 10 as shown above in Fig. 2 and in Fig. 3.
The change of operational mode typically takes place by an operator selecting the second operational mode and giving this as input to the processing circuitry via an input device 42 (see Fig. 4) but it may also take place without the operator, e.g. by detecting via sensor 70 that the ingoing lead roll 33 of the second through-air dryer 12 is absent. This will be explained in more detail below.
The first and second fabrics 21, 22 are preferably structured fabrics, but other kinds of fabric can also be used.
Fig. 4 discloses the processing circuitry 41 that may be operatively connected to various components of the tissue paper machine 1. Dashed lines in Fig. 4 show operative connections of the processing circuitry 41 that may be any connections suitable for transferring signals between the processing circuitry 41 and the components (e.g. wireless connections or connections by wire). Thus, each of the components may have a sender and/or receiver configured to transmit wireless signals, or they may alternatively be connected to the processing circuitry 41 of the control unit 40 by wires.
As shown in Fig. 4, the first through-air dryer 11 is connected to a first burner 51 that is configured to supply heat to the first through-air dryer 11. This may be achieved by the first burner 51 being inside the first through-air dryer 11 , or alternatively by the first burner 51 being placed outside the first through- air dryer 11 with at least one conduit through which a heated medium (typically air) can be transferred from the first burner 51 to the first through- air dryer 11. Also, a first circulation fan 63 is connected to the first through- air dryer 11 and configured to generate an airflow through the porous deck 112. This may be achieved by the first circulation fan 63 being placed inside the first through-air dryer 11 or alternatively by the first circulation fan 63 being connected by at least one conduit to the first through-air dryer 11. When both the first burner 51 and the first circulation fan 63 are engaged simultaneously, air heated by the first burner 51 is blown through the first porous deck 112 so that heat is transferred through the first through-air dryer
11. Furthermore, a first exhaust fan 61 is connected to the first through-air dryer 11 and configured to maintain a mass balance in the air system and remove combustion air from the first burner 51.
Similarly, a second burner 52, a second circulation fan 64 and a second exhaust fan 62 are connected to the second through-air dryer 12.
There may also be additional fans connected to each of the first and second through-air dryers 11, 12, such as a combustion fan that ensures that the first and second burners 51, 52 are supplied with oxygen. One such fan may be provided to each of the first and second through-air dryers 11, 12, or alternatively one fan may be connected to both of the through-air dryers 11 ,
12. In embodiments where one combustion fan is provided for the first burner 51 and another combustion fan for the second burner 52, turning off the second burner 52 means that also the associated combustion fan can be turned off.
The processing circuitry 41 is preferably connected to each of the through-air dryers 11, 12 and each of the burners 51, 52 and exhaust fans 61, 62 and circulation fans 63, 64. Also, the processing circuitry 41 may be connected to the sensor 70 and to the scanner 80, and further to an input device 42 through which manual input from an operator can be received.
To summarize, Fig. 5 discloses the method according to the invention of modifying the tissue paper machine 1, comprising the steps of removing 101 the first fabric 21 and mounting 102 the second fabric 22. The method may also comprise the optional steps of removing 103 the ingoing lead roll 33 of the second through-air dryer 12 and of changing 104 to the second operational mode.
Operation of the modified tissue paper machine 1 will now be described according to a first embodiment of the invention and with reference to Fig. 6.
This method comprises modifying 201 the tissue paper machine 1 as shown in Fig. 5 and operating 202 the tissue paper machine 1 at the second operational mode with the first through-air dryer 11 in a drying mode and the second through-air dryer 12 in an idle mode where the second through-air dryer 12 operates at reduced capacity. The drying mode comprises operating the first through-air dryer 11 to remove moisture from the paper web W transported on the second fabric 22, whereas the idle mode comprises maintaining the second through-air dryer 12 in the tissue paper machine 1 but not operating to remove moisture from the paper web W.
Fig. 7 discloses features of the second operational mode regarding operation of the first burner 51 and first exhaust fan 61, and optional features regarding the second burner 52 and second exhaust fan 62. It also comprises optional features of the rotational speed of the through-air dryers 11, 12.
In step 203, the second operational mode comprises rotating the first through- air dryer 11 at a drying speed and the second through-air dryer 12 at a rest speed. The drying speed of the first through-air dryer 11 is preferably lower than a rotational speed of the first through-air dryer 11 in the first operational mode. It is advantageous to lower the speed of the tissue paper machine 1 as a whole when producing tissue with lower tensile strength, to ensure that the paper web W (that is more fragile than a paper web W with a higher tensile strength) is not damaged. This slower speed in itself causes an increased drying since the paper web W has a longer contact time with the first through- air dryer 11.
Furthermore, the rest speed of the second through-air dryer 12 is preferably lower than the drying speed of the first through-air dryer 11. Even though the second through-air dryer 12 is not used to dry the paper web W, it is advantageous to maintain a rotation of the second through-air dryer 12 to avoid excessive wear on components such as roll bearings that could otherwise arise when the second through-air dryer 12 is completely still and thus exerts a static load on the roll bearings.
In optional step 204, the second operational mode comprises engaging the first burner 51 but not the second burner 52. By engaging only the first burner 51, drying of the paper web W takes place as desired but there is a considerable energy saving since the second burner 52 is not operated.
In optional step 205, the second operational mode comprises engaging both the first and the second exhaust fans 61, 62. The first exhaust fan 61 is thereby operated to ensure drying of the paper web W as described above, whereas operation of the second exhaust fan 62 is advantageous in limiting accumulation of moisture in the second through-air dryer 12. This in turn is highly advantageous in minimizing corrosion.
In some embodiments, drive power of the first through-air dryer 11 may also be increased to enable driving of the second fabric 22 when the second through-air dryer 12 is bypassed. Alternatively, an additional drive roll may be added to ensure that there is sufficient drive power to maintain a desired speed in the drying section 10. As mentioned above, the second operational mode may be initiated by a human operator communicating with the processing circuitry 41 via the input device 42.
Fig. 8 discloses optional steps of initiating the second operational mode without input from an operator. This comprises, in optional step 206, detecting an absence of the ingoing lead roll 33 of the second through-air dryer 12 by means of the sensor 70 (see Fig. 1-3). The sensor may be a proximity switch, an optical sensor or any other suitable type of sensor that is able to detect whether an object is present or not (e.g. an inductive proximity sensor). The sensor may be arranged in connection with the ingoing lead roll 33 or integrated with the ingoing lead roll or may alternatively be arranged at a distance from the ingoing lead roll 33.
In a further optional step 207, the tissue paper machine 1 is operated at the second operation mode in response to the detected absence. This ensures that the processing circuitry 41 is able to initiate the second operational mode without requiring input from an operator, and also provides the additional security that the tissue paper machine 1 is prevented from accidentally operating in the first operational mode even though the tissue paper machine 1 has been modified to fit the second fabric 22 according to the present invention. Since many operational parameters may differ between the first and second operational modes it is advantageous both from the energy efficient and cost standpoints to ensure that the correct operational mode is selected, apart from minimizing the risk of damage to the paper web W if the tissue paper machine 1 should be operated in another mode than intended (e.g. if excessive speed of the tissue paper machine 1 were to be used even though the tensile strength of the paper web W is too low) .
Fig. 9 discloses optional steps for operating the tissue paper machine 1 in the second operational mode to ensure that drying of the paper web W is efficient and achieves the desired dryness before the paper web W is transferred to the Yankee dryer 91. This includes, in optional step 208, setting a desired moisture content for the first through-air dryer 11 in the second operational mode. This is a moisture content that the paper web W should have after having passed the first through-air dryer 11 but before being subjected to the final drying step on the Yankee dryer 91. It is advantageous if the paper web W is sufficiently dry before reaching the Yankee dryer 91 to avoid excessive energy consumption at the Yankee dryer 91, but it is also advantageous if the paper web W still holds sufficient moisture to facilitate transfer to the Yankee dryer 91 in the transfer nip 90. For these reasons, it is advantageous to set the desired moisture content to optimize production of the tissue paper. Suitably, the moisture content going to the Yankee dryer 91 may be in the range 5 - 50 %. Where the Yankee dryer 91 is equipped with a wet-end hood, a dry-end hood, or a full hood covering both wet and dry ends a moisture content can be in the higher end of the range, whereas a lower end of the range is suitable in embodiments where the Yankee dryer 91 is not equipped with a hood.
The method then comprises, in optional step 209, to scan the paper web W downstream of the first through-air dryer 11 to determine an actual moisture content. For this purpose, the scanner 80 is provided in the tissue paper machine 1 as shown in Fig. 1-3. The scanner 80 may scan the paper web W immediately before the transfer nip 90 or in any other location after the first through-air dryer 11 but before transfer to the Yankee dryer 91. It is particularly advantageous to scan the paper web W before the final drying step on the Yankee dryer 91 since this ensures that an effect on the paper web W from drying performed by the first through-air dryer 11 is separated from the effect of the Yankee dryer 91. In some embodiments, the scanner 80 is configured to scan only the paper web W, but in other embodiments the scanner 80 is instead configured to scan the second fabric 22. Also, in some embodiments the scanner 80 is configured to scan both the paper web W and the second fabric 22.
In optional step 210, the actual moisture content determined by the scanner is then compared to the desire moisture content, and in optional step 211 a change of operation of the first through-air dryer 11 to decrease a difference between the actual moisture content and the desired moisture content is determined. The change is then implemented in optional step 212.
The step of scanning 209 the paper web W may then be repeated at desired intervals or continuously, and optionally the desired moisture content may also be changed at regular intervals by automatically updating it or by receiving a manual input from the operator.
Optionally, if the difference between the actual moisture content and the desired moisture content is small, the steps of determining 211 and implementing a change 212 can be skipped so that operation of the first through-air dryer 11 is only changed when a large difference between what the moisture content should be and the real value is determined.
Implementing the change can comprise increasing or decreasing operation of the first burner 51 to in turn increase or decrease the exposure of the paper web W to heat from the first through-air dryer 11. It can also comprise increasing or decreasing operation of the first exhaust fan 61. It may also comprise increasing or decreasing the rotational speed of the first through-air dryer 11 and other properties of the first through-air dryer 11 may also be changed if desired.
It is to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

Claims

1. Method for modifying a tissue paper machine, wherein the tissue paper machine (1) comprises a drying section (10) with a first through- air dryer (11) and a second through-air dryer (12) in serial alignment with each other, each through-air dryer (11, 12) comprising a rotatable cylinder (111, 121) having a porous cylindrical deck (112, 122), and the tissue paper machine (1) further comprising a first fabric (21) wrapped about a portion of a circumference of the first through-air dryer (11) and the second through-air dryer (12), and also comprising a plurality of lead rolls (30) positioned relative to each through-air dryer (11, 12) for directing the first fabric (21) onto and from each through-air dryer (11, 12), and wherein the method comprises:
- removing the first fabric (21) from the tissue paper machine (1), and
- mounting a second fabric (22) wrapped about a portion of the circumference of the first through-air dryer (11) and on at least some of the lead rolls (30) for directing the second fabric (22) onto and from the first through-air dryer (11) but not the second through-air dryer (12).
2. Method according to claim 1, wherein one of the lead rolls (30) is an ingoing lead roll (33) of the second through-air dryer (12), and wherein the method comprises:
- removing said ingoing lead roll (33).
3. Method according to claim 1 or 2, wherein the tissue paper machine (1) further comprises a control unit (40) comprising processing circuitry (41) configured to operate the tissue paper machine (1) in a first operational mode, and wherein the method comprises:
- changing the first operational mode to a second operational mode, wherein said first operational mode corresponds to a first configuration of the tissue paper machine (1) comprising the first fabric (21) and said second operational mode corresponds to a second configuration of the tissue paper machine (1) comprising the second fabric (22).
4. Method of operating a modified tissue paper machine, the method comprising:
- modifying a tissue paper machine (1) according to any of claims 1- 3,
- operating, by processing circuitry (41) comprised in a control unit (40), the modified tissue paper machine (1) at a second operational mode, said second operational mode comprising operating the first through-air dryer (11) in a drying mode for drying a paper web transported on the second fabric (22) and also operating the second through-air dryer (12) in an idle mode.
5. Method according to claim 4, wherein the modified tissue paper machine (1) comprises a first burner (51) configured to supply heat inside the first through-air dryer (11) and a second burner (52) configured to supply heat inside the second through-air dryer (12), and wherein the method comprises
- operating, by said processing circuitry (41), the modified tissue paper machine (1) in the second operational mode to engage only the first burner (51).
6. Method according to claim 4 or 5, wherein the modified tissue paper machine (1) comprises a first exhaust fan (61) and a second exhaust fan (62) for generating a flow of air through the porous cylindrical deck (112, 122) of the first through-air dryer (11) and the second through- air dryer (12), respectively, and wherein the method comprises
- operating, by said processing circuitry (41), the modified tissue paper machine (1) in the second operational mode to operate the first exhaust fan (61) for drying a paper web transported on the second fabric (22) and to operate the second exhaust fan (62) for limiting accumulation of moisture in the second through-air dryer (12).
7. Method according to any of claims 4-6, wherein the method comprises
- operating, by said processing circuitry (41), the modified tissue paper machine (1) in the second operational mode to rotate the first through- air dryer (11) at a drying speed and to rotate the second through-air dryer (12) at a rest speed, said rest speed being lower than the drying speed.
8. Method according to any of claims 4-7, wherein the method comprises
- detecting, by a sensor (70), an absence of an ingoing lead roll (33) of the second through-air dryer (12) of the modified tissue paper machine (1), and
- operating, by the processing circuitry (41), the modified tissue paper machine (1) at the second operational mode in response to the detected absence.
9. Method according to any of claims 4-8, further comprising:
- setting, by the processing circuitry (41), a desired moisture content for the first through-air dryer (11) of the modified tissue paper machine (1) in the second operational mode,
- scanning, by a scanner (80), a paper web downstream of the first through-air dryer (11) to determine an actual moisture content,
- comparing, by the processing circuitry (41), the actual moisture content to the desired moisture content, and
- determining, by the processing circuitry (41), a change of operation of the first through-air dryer (11) to decrease a difference between the actual moisture content and the desired moisture content.
10. Method according to claim 9, further comprising
- implementing, by the processing circuitry (41), said change of operation of the first through-air dryer (11).
PCT/EP2025/057966 2024-04-12 2025-03-24 Method for modifying a tissue paper machine, and method for operating such a machine Pending WO2025214747A1 (en)

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SE2430202A SE2430202A1 (en) 2024-04-12 2024-04-12 Method for modifying a tissue paper machine, and method for operating such a machine

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6910283B1 (en) * 2003-12-19 2005-06-28 Kimberly-Clark Worldwide, Inc. Method and system for heat recovery in a throughdrying tissue making process
US20180363243A1 (en) * 2016-02-29 2018-12-20 Kimberly-Clark Worldwide, Inc. Through-air drying apparatus and methods of manufacture
US20210310191A1 (en) * 2018-11-19 2021-10-07 Valmet Aktiebolag A drying section of a papermaking machine comprising one or more through air drying cylinders

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FI52880C (en) * 1975-11-18 1977-12-12 Valmet Oy Tissue paper machine.
US6673202B2 (en) * 2002-02-15 2004-01-06 Kimberly-Clark Worldwide, Inc. Wide wale tissue sheets and method of making same
US6736935B2 (en) * 2002-06-27 2004-05-18 Kimberly-Clark Worldwide, Inc. Drying process having a profile leveling intermediate and final drying stages

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6910283B1 (en) * 2003-12-19 2005-06-28 Kimberly-Clark Worldwide, Inc. Method and system for heat recovery in a throughdrying tissue making process
US20180363243A1 (en) * 2016-02-29 2018-12-20 Kimberly-Clark Worldwide, Inc. Through-air drying apparatus and methods of manufacture
US20210310191A1 (en) * 2018-11-19 2021-10-07 Valmet Aktiebolag A drying section of a papermaking machine comprising one or more through air drying cylinders

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