Press arrangement and method for pressing a fibrous web
Patent Information
- Application Number
- EP2024707732
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-03-31
- Filing Date
- 2024-02-26
- Publication Date
- 2026-02-11
AI Technical Summary
The production of fibrous webs, particularly packaging paper, faces challenges in reducing energy costs and CO2 footprint due to high energy consumption in the drying section, where increasing line loads in press arrangements can lead to web compression and increased investment costs, while existing press designs struggle to achieve high dry content efficiently without damaging the web.
A press arrangement with a second press operated at a line load of at least 500 kN/m, featuring a geometric design that maintains a quotient of average pressure to peak pressure less than 0.5, allowing for a large press zone length and high peak pressure, and using a polyurethane shoe press jacket for resistance and adhesion, ensuring efficient dewatering without web damage.
This approach significantly increases the dry content of the fibrous web, reduces energy consumption, and lowers the CO2 footprint by preventing web compression while maintaining high peak pressures, making it suitable for packaging paper production with a high proportion of OCC fibers.
Smart Images
Figure EP2024054736_03102024_PF_FP_ABST
Abstract
Description
[0001] Press arrangement and method for pressing a fibrous web
[0002] The present invention relates to a press arrangement for pressing a fibrous web, in particular a packaging paper web, comprising at least two presses arranged one behind the other in the running direction of the fibrous web, namely a first press with a first press nip and a subsequent second press with a second press nip, which is an extended press nip, wherein the second press is designed to be operated with a line load of at least 500 kN / m. Furthermore, the invention relates to a method for pressing a fibrous web, preferably using such a press arrangement.
[0003] Such a press arrangement is described, for example, in the two publications W08808051A1 and WO2017207475A1, the disclosure of which is hereby incorporated by reference.
[0004] Machines for producing a fibrous web usually have a press arrangement in which the fibrous web is dewatered or dehumidified using mechanical pressure. The press arrangement is usually located between the forming and drying sections. A particularly efficient type of mechanical dewatering can be achieved using a so-called extended press nip. The advantages of an extended press nip are well known: The press nip is planar and not essentially linear like in conventional roller presses. As a result, the pressure exerted on the fibrous web to be dewatered in the press nip in the running direction does not set in suddenly, but can be continuously increased from a low value to a high value. This reduces the risk of the fibrous web to be dewatered being crushed in the press nip.In this way, the fibrous web can be dewatered very efficiently in an extended press nip, while at the same time preserving its volume.
[0005] For example, the fibrous web can be guided through the extended press nip together with a felt or between two felts. In a so-called shoe press, the extended press nip can be formed between a shoe press roll and a counter roll. Unlike in the production of tissue webs, the thickness or bulk is less important in the production of paper webs, especially packaging paper webs. For this reason, and because of the considerably higher basis weight of paper webs, especially packaging paper webs, significantly higher line loads are used in the second press nip, namely line loads of at least 500 kN / m.
[0006] The topics of "energy costs" and "carbon footprint" are playing an increasingly important role in the production of fibrous webs. Energy consumption in the dryer section, which is still mostly gas-heated today, is a particularly significant factor. To save energy and gas here, it would be highly advantageous if the fibrous web coming from the upstream press arrangement already had the highest possible dry content. An obvious idea might be to simply increase the line load in the press arrangement to achieve a higher dry content. However, this approach is only of limited practicality, as it carries the risk of the fibrous web to be dewatered being crushed in the press nip.In addition, the energy consumption in the press arrangement also increases with increasing line load at the same machine speed, and with increasing line load the investment costs increase because a considerably more massive frame is required.
[0007] It is an object of the present invention to reduce the energy costs and / or the CO2 footprint for the production of a fibrous web, in particular packaging paper web.
[0008] This object is achieved by the independent claims. The dependent claims relate to advantageous developments of the present invention.
[0009] Specifically, the problem is solved by a generic press arrangement as described above, which is particularly characterized in that the second press is designed in such a way that a quotient of average pressure and peak pressure in the second press nip is less than 0.5.
[0010] The average pressure can be easily determined by dividing the line load by the press zone length of the press arrangement. The line load is the total force applied by the press arrangement divided by the machine width or the width of the press zone over which the total force in the press nip of the press arrangement is distributed. The press zone length is the length in the press nip, measured in the machine direction, over which increased pressure is exerted on the fibrous web. A very low limit can be set for the increased pressure, such as 0.1 MPa above normal pressure. The press zone length is usually a well-known parameter of the press arrangement. It can be easily measured, for example using a pressure film that is inserted into the extended press nip before pressure is applied by the press arrangement. The pressure film then measures which pressure is applied where in the press nip.This also makes it easy to determine the peak pressure in the press nip of the press assembly. Such printing films with various resolutions are commercially available, for example, from Fujifilm under the brand name "Prescale."
[0011] Interestingly, the ratio of mean pressure to peak pressure depends only on the geometric design of the pressing elements that form the extended press nip between them, in particular on the geometric design of any press shoe, but not on the peak pressure. In other words, for a given geometric design, the ratio of mean pressure to peak pressure remains essentially constant even if the peak pressure is increased, since an increase in peak pressure leads to a substantially proportional increase in mean pressure. The ratio of mean pressure to peak pressure thus indirectly describes the geometric design of the pressing elements, in particular of any press shoe.Since there is an incalculably large number of different geometric designs, all of which result in a ratio of mean pressure to peak pressure that is less than 0.5, choosing this ratio seems appropriate to describe the inventive solution. It is important that the value of the ratio of mean pressure to peak pressure can be determined easily and unambiguously for a press arrangement with a fixed design of the pressing elements.
[0012] The inventors have discovered that, with regard to efficient dewatering of the fibrous web, it is particularly advantageous if the geometric design of the pressing elements of the second press, which is operated with a line load of at least 500 kN / m, is selected such that the quotient of average pressure and peak pressure is less than 0.5. The geometric design of the pressing elements of the second press of the press arrangement according to the invention thus differs from known press arrangements, where this quotient is always above 0.5. In order to achieve a quotient of less than 0.5 at a line load of at least 500 kN / m, the product of the pressing zone length and peak pressure must be relatively large. Thus, the present invention preferably describes geometric designs that result in both a relatively large pressing zone length and, at the same time, a relatively large peak pressure.
[0013] The first press, located upstream of the second press, serves to pre-consolidate and dehumidify the fibrous web to such an extent that the fibrous web is not crushed despite a high peak pressure in the second press nip. The press arrangement according to the invention is not limited to the first press and the second press, but can also comprise one or more additional presses if required. In particular, another press can be located upstream of the first press. Preferably, however, no additional press is provided between the first press and the second press.
[0014] In particular, the quotient of average pressure and peak pressure can be less than 0.46 and / or greater than 0.3. A geometric design of the press elements, in particular the press shoe, of the second press, which results in a quotient between 0.3 and 0.46, has proven particularly advantageous in tests for efficient dewatering. Regarding the line load with which the second press can be operated, this can also be significantly higher than 500 kN / m, namely at least 1,000 kN / m, or even at least 1,300 kN / m. As mentioned above, however, there are practical limits to increasing the line load due to an increasing risk of crushing the fibrous web, increasing drive energy, and rising investment costs, particularly for the design of a more solid frame.According to the present invention, the larger the line load is selected, the larger the product of the pressing zone length and the peak pressure must be selected in order to achieve a value of less than 0.5 for the quotient of the average pressure and the peak pressure.
[0015] Good results regarding the dryness increase of the fibrous web in the press arrangement according to the invention can be achieved if the second press is designed to apply a peak pressure of at least 9 MPa, preferably at least 10 MPa, more preferably at least 12 MPa to the fibrous web. These peak pressures are noticeably higher than those in known press arrangements of this type.
[0016] The first press, which in particular has the task of pre-consolidating or dehumidifying the fibrous web so that it can run undamaged through the second press, should fundamentally be designed differently than the second press, even if the first press nip can also be an extended press nip. In particular, the first press should be designed such that at least one of the following statements is true: a) a quotient of average pressure and peak pressure in the first press nip is greater than 0.5; b) the maximum line load with which the first press can be operated is smaller than the maximum line load with which the second press can be operated; c) the peak pressure that can be applied to the fibrous web in the first press nip is smaller than the peak pressure that can be applied to the fibrous web in the second press nip.A preferred embodiment of the invention provides that the second press is a shoe press which comprises a press shoe with a concavely curved surface and a shoe press jacket rotatably mounted around the press shoe.
[0017] It has proven advantageous if the shoe press cover consists at least partially of polyurethane, which is formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and a polyol component containing at least one polyether polyol and / or at least one polycarbonate polyol, and wherein the crosslinking component contains a C2-14 diol. It is further preferred if the polyol component of the prepolymer comprises polytetramethylene ether glycol (PTMEG) and at least one polycarbonate polyol.
[0018] Alternatively or additionally, the crosslinking component can comprise polytetramethylene ether glycol (PTMEG) and / or at least one polycarbonate polyol. A press sleeve with such a polyurethane layer has proven surprisingly resilient, even at high peak pressures. At the same time, this polyurethane mixture is capable of maintaining good adhesion to the reinforcing threads embedded therein, even after many alternating load cycles under high peak pressures.
[0019] According to a further aspect, the present invention relates to a machine for producing a fibrous web, preferably packaging testliner, comprising a previously described press arrangement according to the invention.
[0020] Furthermore, the invention relates to a method for pressing a fibrous web, in particular a packaging paper web, preferably using a previously described press arrangement according to the invention, wherein the fibrous web is guided successively through at least two presses, namely a first press with a first press nip and a subsequent second press with a second press nip, wherein the second press nip is an extended press nip, and wherein the fibrous web is pressed in the second press with a line load of at least 500 kN / m, wherein the fibrous web is pressed in the second press such that a quotient of average pressure and peak pressure in the second press nip is less than 0.5.
[0021] The effects and advantages previously stated with regard to the press arrangement according to the invention also apply mutatis mutandis to the pressing method according to the invention and vice versa.
[0022] Thus, in the method according to the invention, the quotient of mean pressure and peak pressure can be less than 0.46 and / or greater than 0.3.
[0023] Furthermore, the fibrous web can be pressed in the second press with a line load of at least 1,000 kN / m, preferably at least 1,300 kN / m.
[0024] Preferably, the fibrous web is pressed onto the fibrous web in the second press with a peak pressure of at least 9 MPa, more preferably at least 10 MPa, even more preferably at least 12 MPa.
[0025] In the method according to the invention, the first press can also be operated in such a way that at least one of the following statements applies: a) a quotient of average pressure and peak pressure in the first press nip is greater than 0.5; b) the maximum line load with which the first press is operated is smaller than the maximum line load with which the second press is operated; c) the peak pressure applied to the fibrous web in the first press nip is smaller than the peak pressure applied to the fibrous web in the second press nip.
[0026] The method according to the invention can be used particularly efficiently if the fibrous web consists of at least 20 wt.%, preferably at least 50 wt.% OCC fibers. OCC is an abbreviation known in the art and stands for "old corrugated containers." In other words, the press arrangement according to the invention and the pressing method according to the invention are particularly well suited for efficiently pressing fibrous webs that have a significant or even decisive proportion of used fibers, i.e., no fresh fibers. This is related to the high resistance of the OCC fibers to high pressures. The remaining fibers of the fibrous web to be pressed can be selected, for example, from mechanical pulp or wood pulp, such as TMP, CTMP, and / or PGW.
[0027] The invention will be explained in more detail below using an exemplary embodiment described with the aid of schematic figures. In the following:
[0028] Figure 1: a press arrangement according to the invention, comprising a first
[0029] press and a second press;
[0030] Figure 2: an enlarged and detailed view of the second press of the
[0031] Press arrangement shown in Figure 1.
[0032] Figure 1 shows a very schematic illustration of a press arrangement according to the invention, comprising a first press 11 and a second press 1 arranged directly behind it in the direction of movement BR of a fibrous web 8. In this exemplary embodiment, both the first press 11 and the second press 1 are designed as shoe presses and thus each have an extended press nip. Alternatively, however, the first press 11 could also not have an extended press nip and / or the first press 11 and the second press 1 could share a common central roller. The central roller would then be a press element by means of which both the first press nip of the first press 11 and the second press nip of the second press 1 would be formed.
[0033] Figure 2 shows an enlarged and detailed illustration of the second press 1, which is of particular importance according to the invention. This is designed to be operated with a line load of at least 500 kN / m. The second press nip 7 is provided by two press elements, namely a shoe press roll 2 and a counter roll 3. The shoe press roll 2 comprises a press shoe 5, which is supported on a stationary yoke 4, and a shoe press cover 6, which is arranged rotatably around the press shoe 5. Preferably, the fibrous web
[0034] 8 is guided through the second extended press nip 7 in a sandwich-like manner between two press felts 9. The press shoe 5 has a substantially concave surface over which the shoe press cover 6 runs, while the press shoe 5 presses it with a high compressive force F toward the counter roll 3. The geometric design of the press elements, in particular of the press shoe 5, is selected such that a quotient of average pressure and peak pressure in the second press nip 7 is less than 0.5 according to the invention. This quotient can preferably be between 0.3 and 0.46.
[0035] The pressure force F is preferably selected to be so large that the peak pressure acting on the fibrous web 8 in the second, extended press nip 7 is at least
[0036] 9 MPa, more preferably at least 10 MPa, even more preferably at least 12 MPa. In order to achieve a quotient of average pressure and peak pressure in the second press nip 7 that is less than 0.5 according to the invention, with such a high peak pressure and a line load of at least 500 kN / m, the press shoe 5 must be relatively long in order to provide a correspondingly large press zone length for the fibrous web 8 in the second press nip 7.
[0037] At such high peak pressures, it has proven particularly advantageous if the shoe press cover 6 consists at least partially of polyurethane, which is formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and a polyol component containing at least one polyether polyol and / or at least one polycarbonate polyol, and wherein the crosslinking component contains a C2-14 diol. For example, the shoe press cover 6 can have a reinforcing structure made of threads embedded in the polyurethane layer, wherein the prepolymer of the polyurethane layer consists of 50 wt. % of a mixture of 1,4-phenylene diisocyanate (PPDI) and C5-6 polycarbonate diol and 50 wt.-% of a mixture of 1,4-phenylene diisocyanate (PPDI) and polytetramethylene ether glycol (PTMEG), and wherein the crosslinker comprises polytetramethylene ether glycol (PTMEG) and 1,6-hexanediol or is preferably substantially formed therefrom.
[0038] The first press 11, shown schematically in Figure 1, can and preferably is designed differently than the second press 1. In particular, unlike the second press 1, it can be designed such that a quotient of average pressure and peak pressure in the first press nip is greater than 0.5; and / or that the maximum line load with which the first press can be operated is smaller than the maximum line load with which the second press can be operated; and / or that the peak pressure that can be applied to the fibrous web in the first press nip is smaller than the peak pressure that can be applied to the fibrous web in the second press nip. Preferably, all three statements apply. In the press arrangement according to the invention, the first press 11 serves in particular to sufficiently pre-consolidate the fibrous web 8 for passage through the second press 1 so that it is not subjected to undue compression despite a high peak pressure in the second press 1.
[0039] The fibrous web 8 preferably serves for the production of a packaging paper web or is such a packaging paper web. Furthermore, the fibrous web consists of at least 20 wt.%, preferably at least 50 wt.%, OCC fibers, which are characterized by particularly high resistance even to high peak pressures.
[0040] The press arrangement 1 according to the invention could theoretically also comprise more presses than just the first press 11 and the second press 1. However, the second press 1 is preferably the last press of the press arrangement, i.e., the last press before the fibrous web 8 is transferred to a drying section downstream of the press arrangement. Only in exceptional cases may there be a smoothing press after the first press 1 and a downstream drying section, which, however, does not have an extended press nip.
[0041] 1 second press
[0042] 2 Shoe press roll 3 Counter roll
[0043] 4 standing yoke
[0044] 5 press shoe
[0045] 6 Shoe press cover
[0046] 7 second (extended) press nip 8 fibrous web
[0047] 9 Press felt
[0048] 10 Press arrangement
[0049] 11 first press BR direction of movement
[0050] F compressive force
Claims
Patent claims 1. Press arrangement (10) for pressing a fibrous web (8), in particular a packaging paper web, comprising at least two presses (11, 1) arranged one behind the other in the running direction of the fibrous web (8), namely a first press (11) with a first press nip and a subsequent second press (1) with a second press nip which is an extended press nip, wherein the second press (1) is designed to be operated with a line load of at least 500 kN / m, characterized in that the second press (1) is designed such that a quotient of average pressure and peak pressure in the second press nip is less than 0.
5.
2. Press arrangement (10) according to claim 1, characterized in that the quotient of average pressure and peak pressure is less than 0.46 and / or greater than 0.
3.
3. Press arrangement (10) according to claim 1 or 2, characterized in that the second press (1) is designed to be operated with a line load of at least 1,000 kN / m, preferably at least 1,300 kN / m.
4. Press arrangement (10) according to one of the preceding claims, characterized in that the second press (1) is designed to apply a peak pressure of at least 9 MPa, preferably at least 10 MPa, more preferably at least 12 MPa to the fibrous web (8).
5. Press arrangement (10) according to one of the preceding claims, characterized in that the first press (11) is designed such that at least one of the following statements applies: a) a quotient of average pressure and peak pressure in the first press nip is greater than 0.5; b) the maximum line load with which the first press (11) can be operated is smaller than the maximum line load with which the second press (1) can be operated; c) the peak pressure that can be applied to the fibrous web (8) in the first press nip is smaller than the peak pressure that can be applied to the fibrous web (8) in the second press nip.
6. Press arrangement (10) according to one of the preceding claims, characterized in that the second press (1) is a shoe press which comprises a press shoe (4) with a concavely curved surface and a shoe press jacket (6) rotatably mounted around the press shoe (4).
7. Press arrangement (10) according to claim 6, characterized in that the shoe press jacket (6) consists at least partially of polyurethane which is formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and a polyol component containing at least one polyether polyol and / or at least one polycarbonate polyol, and wherein the crosslinking component contains a C2-14 diol.
8. Press assembly (10) according to claim 7, characterized in that the polyol component of the prepolymer comprises polytetramethylene ether glycol (PTMEG) and at least one polycarbonate polyol.
9. Press arrangement (10) according to claim 7 or 8, characterized in that the crosslinking component comprises polytetramethylene ether glycol (PTMEG) and / or at least one polycarbonate polyol.
10. Machine for producing a fibrous web (8), preferably packaging testliner, comprising a press arrangement (10) of one of the preceding claims.
11. Method for pressing a fibrous web (8), in particular a packaging paper web, preferably using a press arrangement (10) according to one of claims 1 to 8, wherein the fibrous web (8) is guided successively through at least two presses (11, 1), namely a first press (11) with a first press nip and a subsequent second press (1) with a second press nip, wherein the second press nip is an extended press nip, and wherein the fibrous web (8) is pressed in the second press (1) with a line load of at least 500 kN / m, characterized in that the fibrous web (8) is pressed in the second press (1) such that a quotient of average pressure and peak pressure in the second press nip is less than 0.
5.
12. Method according to claim 11, characterized in that the quotient of mean pressure and peak pressure is less than 0.46 and / or greater than 0.
3.
13. Method according to claim 11 or 12, characterized in that the fibrous web (8) is pressed in the second press (1) with a line load of at least 1,000 kN / m, preferably at least 1,300 kN / m.
14. Method according to one of claims 11 to 13, characterized in that the fibrous web (8) is pressed in the second press (1) with a peak pressure of at least 9 MPa, preferably at least 10 MPa, more preferably at least 12 MPa.
15. Method according to one of claims 11 to 14, characterized in that the first press (1) is operated in such a way that at least one of the following statements applies: a) a quotient of average pressure and peak pressure in the first press nip is greater than 0.5; b) the maximum line load with which the first press (1) is operated is less than the maximum line load with which the second press (11) is operated; c) the peak pressure applied to the fibrous web (8) in the first press nip is less than the peak pressure applied to the fibrous web (8) in the second press nip. Method according to one of claims 11 to 15, characterized in that the fibrous web (8) consists of at least 20 wt. %, preferably at least 50 wt. % OCC fibers.