Patent Application
20250198085
The present invention relates to a device for dewatering or cleaning a fabric in a paper machine, and to a paper machine comprising such a device. In particular, the paper machine may be a machine for making tissue paper.
Paper machines typically operate by injecting a stock into a forming gap in a forming section to create a paper web that moves through various sections to be formed, dewatered, dried, and optionally structured to form a finished paper. The paper web is transported on a series of wires or fabrics, e.g. felts, that are arranged in endless loops and that serve to form and protect the paper web and optionally also to create a structure in the paper web.
Since the stock typically has a water content of around 97%, removal of water is a main objective when producing paper and this takes place by a combination of pressing, sucking and heating. In some sections of the paper machine, water or air is transported through the wire or felt in order to suck water from the paper web or to allow a flow or hot air to reach the paper web. Some pulp fibers from the paper web will be trapped in the felt or wire or remain on the surface after the paper web has been transferred to further sections in the paper machine, and for this purpose cleaning devices are provided that serve to wash and dry the felts or wires during their return to the point where they once again pick up the paper web.
There are problems associated with current cleaning devices for wires or felts, such as high energy consumption for removing water to render the wires or felts sufficiently dry to be able to receive the paper web. Also, it is difficult to thoroughly clean the wires or felts to remove all remaining pulp fibers in the short time available before the paper web is picked up again.
Dewatering and drying the paper web is also cumbersome, and it is highly desirable to be able to remove as much water as possible before drying stages involving hot air or heated rolls due to the high cost and high energy consumption of heating steam and air.
There is therefore a need for improvements both in cleaning wires or felts and in dewatering the paper web.
The object of the present invention is to eliminate or at least to minimize the problems discussed above. This is achieved by a device for dewatering or cleaning a fabric in a paper machine, and by a paper machine comprising such a device according to the appended independent claims.
The device of the present invention comprises a contact portion arranged on a first side of the device for contacting a fabric in a paper machine, an air device for transporting air to or from the fabric, the air device being operatively connected to at least one opening in the first side for supplying or removing air through the at least one opening, and a vibration generator operatively connected to the contact portion and configured to cause a vibration of the contact portion during operation of the device.
By causing a vibration of the contact portion, the cleaning or dewatering is rendered more efficient since water and any remaining pulp fibers are loosened from the fabric and thus more easily removed by the air device that provides pressurized air or vacuum. Cleaning a fabric is thereby rendered significantly more efficient since a more thorough cleaning can be achieved and remaining pulp fibers removed. At the same time, when using the device for dewatering a fabric that carries a paper web, dewatering is significantly improved so that significant savings in both cost and energy consumption can be achieved. This is both because fewer dewatering devices can be used to arrive at a higher dryness of the paper web and because the remaining moisture content that must be removed by hot air or steam is decreased.
Suitably, the at least one opening is arranged in a downstream end of the first side and the contact portion is arranged in an upstream end of the first side. Thereby, the suction or blowing of air takes place immediately after bringing the fabric to vibrate so that water and optionally also paper fibers that are loosened by the vibrations are immediately removed.
Alternatively, the at least one opening is arranged in an upstream end and the contact portion is arranged in a downstream end of the first side. Thereby, suction or blowing affects the fabric immediately before it is brought to vibrate, and this is highly efficient in removing water and optionally also pulp fibers since the vibrations of the fabric will propagate from the point of contact with the contact portion so that water and optionally also pulp fibers are loosened.
In another alternative, the at least one opening is arranged in the contact portion such that air is supplied to or removed from the fabric through the contact portion. Thereby, suction or blowing takes place at the very place where vibrations are transferred to the fabric, and this is highly efficient in removing water and optionally also residues adhering to or trapped in the fabric.
In some embodiments, only one opening is provided in the device but in other embodiments a plurality of openings are provided and may be placed upstream and/or downstream of the contact portion as well as in the contact portion itself. It is highly advantageous to provide the opening or openings close to the contact portion so that removal of water and optionally residues takes place where the amplitude of the vibrations is large.
In some embodiments for dewatering or cleaning, the air device is a suction device for sucking air from the fabric into the opening. This is advantageous also when the fabric carries a paper web, since it provides efficient suction combined with the vibrations without damaging the paper web. This serves to increase the volume of water that is removed as compared with traditional suctions devices such as Uhle boxes.
In other embodiments for cleaning the fabric, the air device is an air knife for blowing air out of the opening to the fabric. This is advantageous for thoroughly cleaning the fabric since any remaining residues are blown away together with the water, and the combination of the air knife and the vibrations provide a significant improvement over known air knives.
Suitably, the vibration generator is configured to operate with a frequency of at least 10 kHz, preferably at least 15 kHz and more preferably at least 20 kHz. Thereby, the contact portion is brought to vibrate at a suitable frequency that is easily transmitted to the fabric.
The vibration generator may be configured to cause an amplitude of at least 10 μm, preferably at least 15 μm and more preferably at least 20 μm of the contact portion during operation of the device. In some embodiments, the amplitude may be as large as 50 μm. Thereby, the fabric is brought to vibrate so that water is efficiently removed. A larger amplitude is advantageous since it improves removal of water from the fabric.
The device may also comprise at least two contact portions, and the vibration generator may be operatively connected to each of the contact portions and configured to cause them to vibrate independently of each other. This is advantageous in providing a more robust device with a longer lifetime since vibration of one contact portion can take place even where vibration of another has malfunctioned or broken down. Also, frequency and/or amplitude of the contact portions may be varied to increase efficiency in removing water from the fabric. An additional benefit is that multiple contact portions and multiple openings are more efficient in removing water than a single contact portion with a single opening.
In some embodiments, the contact portion is a cylinder, preferably a TAD cylinder for a paper machine, and a plurality of openings are distributed in the contact portion for enabling transport of air through the contact portion. Thereby, the benefits of the present invention are achieved by causing the surface of the TAD cylinder to vibrate.
The present invention also refers to a paper machine comprising a device as defined above. This enables a more efficient removal of water from the fabric in a highly energy efficient and cost-efficient manner as compared with known prior art solutions. The paper machine of the invention comprises at least one device according to the invention but may optionally comprise a plurality of devices that are used for dewatering or cleaning or both.
Suitably, at least one device is arranged in a forming section of the paper machine and configured to dewater a first fabric carrying a paper web. Thereby, dewatering in the forming section is improved to render the water content lower when the paper web is transferred to the subsequent section.
At least one device may be arranged in a press section of the paper machine and configured to dewater a second fabric carrying a paper web. Thereby, dewatering in the press section is improved so that subsequent cleaning and optionally also drying is improved.
Suitably, at least one device is arranged in a structuring section of the paper machine and configured to dewater a third fabric carrying a paper web. Thereby, dewatering in the structuring section is improved so that water content is lowered before a final drying stage.
In some embodiments, the structuring section is a through air drying section, TAD. Thereby, the combined structuring and drying may be improved to decrease the need for heated air.
Suitably, at least one device is arranged in a drying section of the paper machine and configured to dewater a fabric carrying a paper web. Thereby, removal of remaining moisture in the paper web is rendered more efficient so that consumption of steam or hot air is be decreased.
At least one device is suitably arranged in a cleaning section for cleaning a fabric. Thereby, cleaning of the fabric is improved as compared to prior art cleaning sections.
Many additional benefits and advantages of the present invention will be readily understood by the skilled person in view of the detailed description below.
The invention will now be described in more detail with reference to the appended drawings, wherein
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.
In the context of the present invention, the term “fabric” is used to refer to any wire, band, structured fabric or belt that is used in a paper machine for forming or carrying a paper web. Such bands or belts include wires such as forming wires and structuring wires and also include felts and other textiles used in paper machines.
A paper machine is used herein to refer to any machine suitable for producing paper from a pulp. Such machines include, but are not limited to, machines for producing tissue paper, paper, and paperboard.
When it is stated herein that two components are operatively connected to each other, this is to be understood as the components being connected to each other in such a way that a signal, a movement or a force can be transmitted from one to the other. Thus, that a vibration generator is operatively connected to a contact portion is to be understood as the vibration generator being able to bring the contact portion to vibrate.
The terms “upstream” and “downstream” are used herein in relation to a movement direction of a fabric or a paper web in a paper machine. Thus, a location that is upstream of another is a location that any given point on the fabric or paper web passes before arriving at the other. The terms “before” and “after” are used to denote that any given point on the fabric or paper web passes a location “before” another at an earlier point in time than a location that is “after” the other.
A paper web is defined as pulp fibers travelling together on a fabric to form a continuous web from a forming nip, where the paper web is formed by a pulp suspension, to a roll section where the paper web arrives as a finished paper. “Trapped residues” or simply “residues” are used to denote substances or particles of the paper web that remain in or on a fabric after the paper web is transferred to a subsequent section of the paper machine. Such substances or particles include adhesives, coating, dirt, and pulp fibers, among others.
The invention will now be described, starting with one embodiment of a device shown schematically in
The contact portion 2 is operatively connected to a vibration generator 5 that is configured to cause a vibration of the contact portion 2 when the device 1 is in use. The vibration generator 5 is shown as connected to the contact portion 2 by a connection 5′ but in some embodiments the vibration generator 5 may be integrated with the contact portion 2 or be arranged to contact the contact portion 2 without the connection 5′. The vibration generator 5 is suitably connected to a power source (not shown). The device 1 suitably also comprises a housing 6 in which at least some of the components of the device 1 are arranged.
The contact portion 2 may extend along an entire length l of the device 1 on the first side A of the device 1 but may in other embodiments comprise only one portion of the length l. Also, in some embodiments the contact portion 2 extends across an entire width w of the device 1 but may in other embodiments comprise only one portion of the width w. The length l is defined as an extension of the device 1 on the first side A in a direction of travel of the fabric F, whereas the width w is an extension of the device 1 on the first side A in a direction that is perpendicular to the length l.
In some embodiment, the contact portion 2 is a single portion of the device 1 but in other embodiments the device 1 may comprise a plurality of contact portions 2 that are connected to the vibration generator 5 either individually or jointly.
The device 1 also comprises an air device 4 for transporting air to or from the fabric F and further comprises at least one opening 3 in the first side A for supplying or removing air. The at least one opening 3 may be either an opening in the contact portion 2, upstream of the contact portion 2, downstream of the contact portion 2, or a combination of these options. In some embodiments, there may also be at least one opening 3 parallel to the contact portion 2, i.e. beside the contact portion 2 in a direction transversal to the travel direction D of the fabric F. In most embodiments, a plurality of openings 3 are arranged in the first side A, but it is to be noted that a single opening 3 is also possible within the scope of the invention.
When the at least one opening 3 is arranged upstream US of the contact portion 2, it follows that the contact portion 2 is downstream DS of the at least one opening 3, and vice versa.
The first side A of the device 1 may comprise both the housing 6 and the contact portion 2, and the at least one opening 3 is an opening in the first side A by extending into the device 1 through the housing 6 or through the contact portion 2. Where a plurality of openings 3 are provided, these may be openings 3 in the housing 6, in the contact portion 2, or both.
In some embodiments (see
The air device 4 is connected to the at least one opening 3 by an air connection 4′, suitably a tube or conduit so that air is able to pass between the air device 4 and the opening(s) 3. The device 1 also comprises a transport connection 4″ that may suitably be a tube or conduit for transporting air between the air device 4 and a separate unit (not shown).
The air device 4 is in some embodiments a suction device such as an Uhle box or similar that operates by generating a negative pressure (typically referred to as a vacuum) and thereby sucking air into the opening(s) 3 to the air device 4. In such embodiments, the transport connection 4″ may lead to a receiving vessel for receiving air along with water, residues and optionally also other substances such as dirt or particles from the fabric F. The air device 4 suitably generates a negative pressure of at least 10 kPa, more suitably at least 30 kPa or even more suitably at least 65 kPa.
In other embodiments, the air device 4 is instead an air knife that operates by blowing pressurized air through the at least one opening 3. In such embodiments, the transport connection 4″ may lead to a source of pressurized air. The pressurized air is suitably supplied at a pressure of at least 0.5 bar, more suitably at least 5 bar and even more suitably at least 10 bar. A higher pressure is advantageous in improving removal of water and optionally also residues from the fabric.
The vibration generator 5 is configured to cause the contact portion 2 to vibrate and thereby to create a vibration in the fabric F as it travels past the device 1 during operation. In some embodiments of a paper machine, the device 1 is configured to contact the fabric F but in other embodiments the device 1 may instead be arranged close to the fabric F such that vibrations of the contact portion 2 brings it into contact with the fabric F or alternatively that vibrations of the contact portion 2 close to the fabric F causes the fabric F to vibrate also. Suitably, the vibration generator 5 is configured to operate the contact portion 2 with a frequency of at least 10 kHz, preferably at least 15 kHz and more preferably at least 20 kHz. Having a higher frequency causes more intense vibrations of the fabric F and thereby aids in releasing trapped water and residues. The vibration generator 5 is in some embodiments configured to cause an amplitude of at least 10 μm, preferably at least 15 μm and more preferably at least 20 μm. In some embodiments, the amplitude may be 50 μm or more. In both low-frequency and high-frequency embodiments, a larger amplitude is advantageous since it further increases release of water and residues from the fabric F.
The contact portions 2a, 2b suitably comprise sheet metal that is easily brought to vibrate by the transducers 5.
By the vibration generator 5 being operatively connected to each of the contact portions 2a, 2b, they are able to vibrate independently of each other. This may be caused by separate transducers for each of the contact portions 2a, 2b as shown in
In some embodiments, the contact portions 2a, 2b are in this way configured to vibrate at different frequencies and/or with different amplitudes, but in other embodiments they may instead be configured to vibrate with the same frequency and/or amplitude.
In some embodiments, the contact portions 2a, 2b are instead connected to the vibration generator 5 in such a way that they vibrate together.
In a third embodiment, the contact portion 2 is in the form of a cylinder of part of a cylinder with the first side A being an outside of the cylinder. The at least one opening 3 is in this embodiment a plurality of openings 3 that are distributed in the contact portion so that transport of air through the contact portion 2, i.e. from an inside of the cylinder to an outside (blowing) or from the outside of the cylinder to the inside (sucking), is enabled. Suitably, the device 1 in this embodiment forms a TAD (through air drying) cylinder that is configured to provide improved drying of the paper web by the combination of vibration of the contact portion 2 and the air flow through the plurality of openings 3.
For all embodiments disclosed herein disclosing the air device 4 as a suction device, the device 1 may be modified to instead have the air device 4 as an air knife. Similarly, where an embodiment is described with an air knife this may be changed to a suction device without requiring substantial modifications to the device 1 as such. In some embodiments, the air device 4 may also have a double function and be configured to switch between a suction function and a blowing function.
A paper machine 100, 100′ according to the invention will now be described with reference to
The paper machine 100 comprises a forming section 10 where stock comprising diluted pulp is injected into a forming nip between a first fabric 71 that may be referred to as a forming fabric and a second fabric 72 that may be referred to as an inner wire. This causes creation of a paper web P that is transported on the second fabric 72 through the press section 20 for pressing and dewatering. The paper web P is then transferred to a third fabric 73 that may be referred to as a structuring fabric and is transported through the structuring section 30 for structuring and drying on at least one but suitably two dryer rolls 31, 32. Afterwards, the paper web P is transferred to a drying section 40 that suitably comprises a Yankee dryer for removing remaining moisture and from which the finished paper is transferred to a roll section 50 for rolling. This operation of a through air dryer TAD is well-known within the art.
The first, second and third fabrics 71, 72, 73 each form endless loops and are configured to travel in a machine direction M when carrying the paper web P and return in an opposite direction when the paper web P has been transferred to a subsequent section. During the return, each of the fabrics 71, 72, 73 is cleaned. For the third fabric 73, a cleaning section 60 is provided to allow for a thorough cleaning and drying.
In the press section 20, at least one device 1 can be arranged to dewater the second fabric 72 and thereby the paper web P by combining the vibrations of the contact portion 2 with negative pressure from the air device 4 acting as a suction device. This has the advantage of the causing the paper web P to adhere more firmly to the second fabric 72 as well as efficiently dewatering the second fabric 72 and thereby the paper web P.
In the structuring section 30, at least one device 1 can be arranged to dewater the third fabric 73, either before the dryer rolls 31, 32, between them or after them. Similar to the use of the device 1 in the press section 20, the air device 4 is configured to act as a suction device by providing a negative pressure to dewater the third fabric 73. This has the same advantages as when used in the press section 20 by combining efficient dewatering and improved adherence to the third fabric 73.
In the cleaning section 60, at least one device 1 can be arranged inside a cleaning station (not shown) where the third fabric 73 is washed by supplying a cleaning fluid such as water and dried by dewatering.
In the prior art, cleaning generally takes place by spraying cleaning fluid at high pressure onto the fabric and by using at least one Uhle box or air knife to suck fluid from the fabric or blow the fluid away from the fabric.
In the paper machine 100 of the present invention, at least one such Uhle box or air knife can be replaced with a device 1 according to the invention. When cleaning the third fabric 73, it is advantageous to provide the device 1 with the air device 5 acting as a suction device since this increases efficiency in removing fluid as compared to a traditional Uhle box. However, it is also advantageous to provide the device 1 with the air device 5 configured to blow pressurized air on the third fabric 73, since this efficiently removes fluid and the third fabric 73 does not carry the paper web P while in the cleaning section 60.
It is particularly advantageous to combine at least one device 1 acting as a suction device in the cleaning section 60 with at least one device 1 acting as an air knife to supply pressurized air to the third fabric 73, since this provides both a thorough cleaning and a drying of the third fabric 73. Devices 1 of the invention may be provided either before the third fabric 73 enters the cleaning station 61, inside the cleaning station 61, or after the cleaning station 61, or any combination thereof.
In the forming section 10, at least one device 1 according to the invention can be arranged to dewater or clean the first fabric 71 during its return to the forming nip FN. The device 1 may be configured as a suction device or as a blowing device, and where more than one device 1 are provided they may be configured in the same way or in different ways.
The drying section 40 may optionally also comprise a device 1 according to the invention arranged before a drying on the Yankee dryer 41.
Among the many possible placements of the device 1 according to the present invention, it may be particularly advantageous to provide the device 1 in connection with the first roll downstream of the forming nip FN. It may also be particularly advantageous to provide the device 1 in connection with the rolls that transfer the paper web to the third fabric 73 or downstream of these rolls but upstream of the TAD cylinders.
Thus, the paper machine 100′ of the second embodiment comprises the forming section 10′ where stock is injected into a forming nip FN′ and formed between the first fabric 71′ (that may be referred to as a forming fabric) and the second fabric 72′ (that may be referred to as a felt) to create the paper web P′. In the press section 20′, the paper web P′ is carried on the second fabric 72′ and is pressed and dewatered before reaching the drying section 40′ where it is transferred to a Yankee dryer 41′ to remove remaining moisture before being transferred to the roll section 50′ for rolling. As in the first embodiment, the first fabric 71′ and second fabric 72′ are cleaned during their return and for the second fabric 72′ the cleaning section 60′ is provided with the cleaning station 61′.
The device 1 of the present invention may be provided in any of the forming section 10′, press section 20′ and cleaning section 60′. For setups where the drying section 40′ comprises components before the Yankee dryer 41′, at least one device 1 may also be arranged in the drying section 40′.
As for the first embodiment, the device 1 is suitably used for dewatering the paper web P′ where it is carried by the second fabric 72′ and the air device 5 is configured as a suction device in order to protect the paper web P′ and improve adherence to the second fabric 72′.
Where the device 1 is arranged in connection with the first fabric 71′, or with the second fabric 72′ in the cleaning station 60′ or where the second fabric 72′ does not carry the paper web P′, the air device 5 is suitably configured either as a suction device, similar to a Uhle box, or as a blowing device, similar to an air knife. The combination of the vibrations with suction is highly advantageous in cleaning and dewatering the first fabric 71′ or second fabric 72′, and the combination of the vibrations with blowing pressurized air is highly advantageous in cleaning and drying the first fabric 71′ or the second fabric 72′.
The device 1 of the present invention may be mounted in the paper machine 100, 100′ during manufacture of the paper machine 100, 100′, but may also be used to retrofit existing paper machines to form the inventive paper machine 100, 100′ by adding at least one device 1 according to any embodiment of the invention as disclosed herein.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2230161-8 | May 2022 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/061669 | 5/3/2023 | WO |
