Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/66—Pulp catching, de-watering, or recovering; Re-use of pulp-water
  • D21F1/80—Pulp catching, de-watering, or recovering; Re-use of pulp-water using endless screening belts
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F3/00—Press section of machines for making continuous webs of paper
  • D21F3/02—Wet presses
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F3/00—Press section of machines for making continuous webs of paper
  • D21F3/02—Wet presses
  • D21F3/06—Means for regulating the pressure
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F7/00—Other details of machines for making continuous webs of paper
  • D21F7/06—Indicating or regulating the thickness of the layer; Signal devices
• • 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
  • D21F9/003—Complete machines for making continuous webs of paper of the twin-wire type

Definitions

• the present invention concerns a twin wire press and a method for dewatering a fibre suspension in a twin wire press.
• Twin wire presses for dewatering a fibre suspension and forming a continuous fibre web are known.
• the pulp is normally dewatered from an incoming pulp concentration of 3-8 % (weight) to an outgoing pulp concentration of 30-50 % (weight).
• Such twin wire presses known in the art comprise lower rolls, a continuous lower wire running as a web around said lower rolls, upper rolls, and a continuous upper wire running as a web around said upper rolls. Both wires interact along a dewatering section of said webs, in which section the wires form a wedge shaped space for the fibre suspension. While moving along said dewatering section, the wires thus gradually compress the fibre suspension in the wedge shaped space, whereby the fibre suspension is initially pressed and dewatered and formed to a cohesive fibre web between the wires.
• a head box supplies the fibre suspension to the wedge shaped dewatering space between the respective wires.
• the known twin wire press has double dewatering tables supporting the wires in the dewatering section of the web, forming the wedge shaped dewatering space between the wires, and an arrangement of rolls provided after the dewatering tables, seen in the direction of the wires, for final pressing and dewatering of the fibre web between the wires, giving the fibre web a desired dry matter content.
• Perforated dewatering elements are provided along the length of the wires in the wedge shaped dewatering space, bearing on the wires outside the dewatering space.
• the formed filtrate flows through the wires and the perforated dewatering elements and is diverted to an upper and lower discharge box, respectively arranged at the dewatering tables.
• the upper and lower discharge box respectively can be divided into several chambers, whereby the filtrate flowing through the upper and lower dewatering element, respectively, can be divided into partial filtrates in two or more chambers in the discharge box respectively.
• the dewatering tables in a twin wire press constitutes the first step of the dewatering of a fibre suspension, and is adapted to relatively slow dewatering and also for preparing the fibre web, formed by the dewatering of the fibre suspension, for the much faster dewatering taking place in the following arrangement of rolls by pressing in a roll nip.
• Too high load on the dewatering tables directly results in high friction and also very high energy consumption. It is a considerable step from the relatively slow dewatering in the dewatering tables to the very fast dewatering in the arrangement of rolls, and this sometimes results in problems in the first roll nip in the arrangement of rolls.
• the fibre web has too low pulp concentration leaving the dewatering tables, entering and deforming with too high speed in the first roll nip of the arrangement of rolls, the fibre web can be damaged.
• An aim of the present invention is to at least partially eliminate the disadvantages of the prior art described above.
• a general objective of the present invention is to achieve a simplified and improved dewatering and pressing in a twin wire press. More particularly, it is an objective to reduce the friction loads on the fibre web, and the difference between the relatively high friction load of the dewatering tables and the relatively considerably lower friction load in the first roll nip in the arrangement of rolls.
• An additional objective is to be able to increasingly reduce the rewetting of the fibre web in the pressing in the arrangement of rolls to produce a fibre web with higher dry solids content.
• a further objective is to reduce the cost for manufacturing a twin wire press, and reduce the cost for dewatering and pressing in a twin wire press.
• twin wire press for dewatering a fibre suspension according to the present invention, as apparent from claim 1 of the attached claims, which twin wire press comprises a continuous lower wire and a continuous upper wire, which delimit an elongated dewatering space, in which the fibre suspension is dewatered during movement of the wires.
• the twin wire press comprises a head box for supplying the fibre suspension to the dewatering space at an inlet end of the dewatering space and double dewatering tables supporting the wires respectively. A fibre web is formed between the wires.
• the twin wire press further comprises an arrangement of rolls after the dewatering tables, seen in the direction of movement of the wires, for final pressing and dewatering of the fibre web between the wires, giving the fibre web desired solid matter content.
• the twin wire press is characterized by the arrangement of rolls comprising at least a first dewatering control means having a dewatering element forming a press nip with a first roll, or alternatively with another dewatering control means.
• the press nip is placed directly after the dewatering tables, seen in the direction of movement of the wires, where the dewatering element of the first dewatering control means presses the formed fibre web against the first roll, or the alternative second dewatering control means, through the wires, whereby the water displaced from the fibre web by the dewatering element is at least partially drained through the dewatering element.
• the dewatering element of the first dewatering control means and the first roll, respectively, or the alternative second dewatering control means and corresponding second dewatering element, along a section of the press nip where they bear on each other, are at least partially adapted to each other to provide a chosen thickness profile, which chosen thickness profile is designed to provide the twin wire press with a desired dewatering profile.
• the at least partial adaptation does not necessarily mean that the corresponding dewatering elements have the same shape.
• dewatering profile relates to the variation of the fibre web thickness along the dewatering length while in connection with the dewatering element.
• the present twin wire press and the inventive process provide means to regulate the dewatering profile, which in turn provide ways to control the dewatering mode, the dewatering rate, the compression mode, and/or the compression rate of the dewatering process.
• One important aspect of the present invention is that it provides a possibility to control the variation of the compression rate by regulating the shape of dewatering element(s).
• the angle of attack can be controlled by way of the dewatering control means, which in turn impacts on the dewatering length.
• the deformation change is controlled by means of the shape of the dewatering element, while the dewatering length - that is the distance over which the web is subjected to load - is controlled by means of the dewatering element(s) position(s) in relation to opposing dewatering element (a roll, for instance).
• a dewatering element can be exchanged for another one of different shape, depending, for instance, on the kind of pulp used, production capacity, the length of the preceding wedge-shaped dewatering zone, in order to optimize deformation change for a given process.
• the shape of a dewatering element can for instance be concave or convex, depending on the desired deformation rate.
• a dewatering element made of another material can be used, where the choice of material influences the dewatering profile.
• dewatering control means is to control the corresponding dewatering element; the latter are essentially in contact with the respective wires, whereas the former are essentially not in such contact.
• the introductory press nip in the arrangement of rolls provides a particularly effective pressing for dewatering, capable of individual adjustment, independently of the load on the fibre web caused thereafter by the arrangement of rolls.
• the present invention is capable of reducing the friction load and compensating the difference of friction load between dewatering table and the arrangement of rolls.
• a major part of the white water flow can be diverted through the dewatering element, a reduced rewetting of the fibre web is achieved.
• a minor part of the white water can also be led back, as in the case of an ordinary roll nip, i.e.
• the dewatering element can be allowed a longer dewatering length and more effective dewatering, whereby a higher dry solids content of the fibre web can be achieved before a first roll nip in the arrangement of rolls.
• the cost for manufacturing a twin wire press can be reduced by reduction of the number and size of the rolls.
• the method for dewatering and pressing in a twin wire press can be performed with higher cost-efficiency.
• the device according to the present invention can be applied to existing twin wire presses and can, where applicable, replace the present first pair of rolls in a roll nip of a twin wire press.
• the press nip comprises a first roll.
• the dewatering element of the first dewatering control means, pressing the formed fibre web against the first roll through the wires can have a shape in the section where they adjoin and where dewatering takes place, substantially corresponding to the shape of the mantle area of the roll.
• said press nip can comprise a second dewatering control means which is not a traditional roll.
• Said first and second dewatering control means with their respective dewatering element can, in this respect, have a shape at least partially adapted to each other along that section of the press nip where they bear on each other.
• the second dewatering control means comprises a dewatering element.
• the first dewatering control means may be adjustably arranged for being movable vertically and horizontally in relation to the first roll, or the alternative second dewatering control means, providing for optionally adjusting the thickness profile, thus allowing continuous control of desired dewatering profile of the twin wire press.
• the first roll may, for instance, be smooth, perforated or have rills. If the first roll is perforated or rilled, this can improve the dewatering so that the flow of white water can be led forward in the press nip, i.e. in the direction of movement of the wires.
• the arrangement of rolls can comprise a second roll, arranged to the first dewatering control means, directly after the dewatering element, seen in the direction of movement of the wires, where the second roll presses the formed fibre web against the first roll, or the alternative second dewatering control means.
• the dewatering element of the first dewatering control means has a front section, a middle section, and a rear section.
• the front section can be shaped as a round section, with an inlet radius, against which the wire runs and first enters immediately before the wires enter the press nip between the first dewatering control means and the opposite first roll, or the alternative second dewatering control means.
• a dewatering force can form when the wires are strained around this inlet radius before the wires are pressed by the opposite first roll, or the alternative second dewatering control means. This inlet radius of the dewatering element can thus improve the dewatering.
• the middle section of the dewatering element may have a longitudinal shape substantially following the radius of the opposing first roll, or the alternative second dewatering control means, in the press nip.
• the rear section of the dewatering element can exhibit a wedge shaped section.
• the dewatering element has in the rear section an extension diverging from the wires and is not in contact with the wires.
• the middle section of the dewatering element may comprise a perforated dewatering element.
• the middle section constitutes a so called dewatering zone.
• Perforations in the shape of holes in such a perforated dewatering element may be placed in the beginning of the middle section, immediately after the inlet radius of the front section. Further, holes may be placed in the end of the middle section immediately before the wedge shape of the rear section.
• the wedge shape of the rear section directly after the dewatering zone, in combination with the design of the dewatering control means, makes it possible to divert liquid and only minimal force is lost to rewetting.
• the present invention also concerns a method for dewatering of a fibre suspension in a twin wire press, having a continuous lower wire and a continuous upper wire, and a first and a second dewatering table, supporting the wires and forming an elongated wedge shaped dewatering space limited by the wires.
• the wires displace the fibre suspension during the compression of the wires by the dewatering tables, so that the fibre suspension is dewatered and forms a fibre web between the wires.
• An arrangement of rolls is placed after the dewatering tables, seen in the direction of movement of the wires, for final pressing and dewatering of the fibre web between the wires, giving the fibre web a desired dry solids content.
• the method is characterized by dewatering and pressing taking place in a first press nip in the arrangement of rolls, through applying a first dewatering control means having a first dewatering element to press the formed fibre web against a first roll, or an alternative second dewatering element, through the wires.
• the water pressed from the fibre web by the dewatering element is at least partially drained through the dewatering element.
• Fig. 1A schematically shows in a partial view a longitudinal section of an inlet section of an arrangement of rolls of a twin wire press according to the present invention
• Fig. 1 B schematically shows an enlarged view of the inlet section shown in Fig. 1A
• Fig. 2 schematically shows an overview of a longitudinal section through a twin wire press according to an embodiment of the present invention, which can comprise the press nip with the embodiment shown in Fig. 1.
• the arrangement of rolls 4 has an inlet section 6.
• Fig. 1A-B shows partial and enlarged views of the inlet section 6 in the arrangement of rolls 4 of the twin wire press 2 according to an embodiment of the present invention.
• the twin wire press 2 comprises a continuous lower wire 8 and a continuous upper wire 10, which delimit an elongated dewatering space 12, in which the fibre suspension is dewatered during movement of the wires 8,10.
• the twin wire press comprises a head box 14 for supplying the fibre suspension to the dewatering space 12 at an inlet end of the dewatering space and double dewatering tables 16,18 supporting the wires, respectively.
• a fibre web F is formed between the wires.
• the arrangement of rolls 4 is placed after the dewatering tables 16,18, seen in the direction of movement of the wires, for final pressing and dewatering of the fibre web F between the wires, giving the fibre web a desired dry solids content.
• the arrangement of rolls 4 comprises at least a first dewatering control means 22 having a dewatering element 24 forming a press nip 25 with a first roll 26, or the alternative with a second dewatering control means (not shown).
• the press nip 25 is placed in the inlet section 6 of the arrangement of rolls 4, directly after the dewatering tables, seen in the direction of movement of the wires 8,10, where the dewatering element 24 of the first dewatering control means presses the formed fibre web F against the first roll 26, or the alternative second dewatering control means, via the wires 8,10, whereby water pressed from the fibre web F by the dewatering element 24 is at least partially drained through the dewatering element 24.
• the twin wire press 2 may comprise a frame for the roll arrangement 4 of the press.
• the frame comprises a first upper pair 28 and a second lower pair 30 of side elements extending longitudinally. It is intended that rolls are arranged between said first upper and second lower side elements 28,30 in the twin wire press 2.
• the first dewatering control means 22 is arranged in connection to the dewatering and pressing space between the wires 8,10 at the upper side element 28.
• the first dewatering control means 22 is arranged to place a separate pressing force P on the upper wire 10, so that this wire presses the formed fibre web F through the lower wire 8 against the lower first roll 26, or the alternative second dewatering control means, to press water out of the fibre web at least partially dewatered through the dewatering element 24.
• the first dewatering control means 22 is provided to adjust the separate pressing force P so as to achieve the desired dry solids content of the fibre web leaving the press nip 25.
• the separate pressing force P is adjusted independently of the load on the fibre web caused by the subsequent pair of rolls in the arrangement of rolls.
• the dewatering control means 22 is arranged to extend across substantially the entire length L of the twin wire press 2.
• the dewatering control means 22 can have the shape of a beam or similar.
• the first dewatering control means 22 is an upper dewatering control means and the first roll 26 is a lower roll. Alternatively, if the first roll 26 is replaced by a second dewatering control means, this is a lower dewatering control means.
• control of the dewatering profile i.e. the variation of fibre web thickness D along the length of the dewatering element
• the first dewatering control means 22 can be adjustably arranged, for movement vertically V and horizontally H in relation to the first roll 26, or the alternative second dewatering control means, for adjusting the dewatering length and dewatering profile for the dewatering element 24 in the press nip 25.
• the first dewatering control means 22 can comprise at least one adjustment means.
• the first dewatering control means 22 can be arranged to a side element 28 over a support means 32 at an upper end 34 of the first dewatering control means 22.
• the upper end 34 is pivotably arranged on bearings around a pivot axis (not shown) of the support means 32 arranged to the side element 28, here the upper side element 28.
• the corresponding support means 32 for the first dewatering control means 22 can be arranged in multiple positions across the length L of the twin wire press 2, which can makes it possible to achieve the right straightness in the press nip 25.
• a first control means 36 such as a screw-like element, is adjustably arranged in association with a protruding extension part 38 at a first outer end 40 of the first dewatering control means 22 by the upper side element 28.
• the first control means 36 is provided to adjust how far down the first dewatering control means 22 can be pressed against the dewatering and pressing space between the wires 8,10 and the lower roll 26, alternatively the second dewatering control means.
• the first control means 36 limits the movement of the first dewatering control means 22 towards the dewatering and pressing space between the wires 8,10, substantially in a vertical direction V (see the arrow P1 ; as shown in Fig.
• the control means 36 is aimed in a somewhat inclined direction, closer to vertical V than horizontal H), so that there always will be a certain space between the wires 8,10.
• the first control means 36 aims at preventing the first dewatering control means 22 from straining the lower roll 26, alternatively the second dewatering control means, when there is no fibre web F between the wires 8,10, which otherwise would result in damages on the wires 8,10, as well as preventing a total closure of the space between the wires 8,10.
• a too low concentration of the fibre web F, for example, can lead to it breaking completely.
• a second control means 42 such as a screw-like element, is adjustably arranged in association with a second outer end 44 of the first dewatering control means 22 at the upper side element 28.
• the second control means 42 is provided to adjust the first dewatering control means 22 substantially in a horizontal direction H (see arrow P2) for correct positioning of the dewatering element 24 above the lower roll 26, alternatively the second dewatering control means.
• the second dewatering control means can comprise an adjustment device that substantially corresponds to the adjustment device for the first dewatering control means 22 described above.
• the dewatering element 24 of the first dewatering control means 22 and the first roll 26, respectively, or the alternative second dewatering control means, along a section of a press nip 25 where they bear on each other have a design at least partially adapted to each other.
• said press nip 25 comprises a first roll 26, where the dewatering element 24 of the first dewatering control means 22, pressing the formed fibre web against the first roll 26 through the wires 8,10, can have a shape along the section where the dewatering element and the first roll adjoin each other, that substantially corresponds to the shape of the mantle area 46 of the roll 26.
• said press nip 25 can include a second dewatering control means, which is not a traditional roll.
• the respective dewatering element with attached respective dewatering control means have a design at least partially adapted to each other along the section of the press nip 25 where they bear on each other, i.e. a respective geometrical shape adapted to each other, along a section where they bear on each other. Accordingly, this differs from a roll nip where only two radiuses bear on each other.
• the second dewatering control means can include a dewatering element which, for all practical purposes, corresponds to the dewatering element 24 described herein.
• the first roll 26 may, for instance, be smooth, perforated, grooved, or rilled.
• the first roll is may be provided with holes or rills, which can improve the dewatering so that the white water flow can be guided forward in the press nip 25, i.e. in the direction of the direction of the movement of the wire.
• the arrangement of rolls 4 includes a second roll 48, arranged to the first dewatering control means 22, directly after the dewatering element 24, seen in the direction of movement of the wires, where the second roll 48 presses the formed fibre web F against the first roll 26, or the alternative second dewatering control means.
• the press force between the previous first dewatering control means 22 and the first roll 26, or the alternative second dewatering control means does not have be the same as in the following roll nip, so that the fibre web runs the risk of delamination in the introductory press nip 25.
• this second roll 48 does not have to be of the same size as the rolls normally used in subsequent nips with roll pairs.
• the dewatering element 24 of the first dewatering control means 22 has a front section 24A, a middle section 24B, and a rear section 24C.
• the front section 24A is designed having a rounded section, with an inlet radius 24R, against which the wires 8, 10 run and first enters immediately before the wires enter press nip 25 between the first dewatering control means 22 and the opposing first roll 26, or the alternative second dewatering control means.
• a dewatering force can form when the wires 8, 10 are pulled around this inlet radius 24R before the wires 8, 10 are pressed by the opposite first roll 26 or the alternative second dewatering control means.
• this inlet radius 24R of the dewatering element 24 can result in improved dewatering.
• the middle section 24B of the dewatering element 24 has a longitudinally extending shape 24L substantially following the radius R of the opposing first roll 26, or the alternative second dewatering control means, in the press nip 25.
• the rear section 24C of the dewatering element 22 can exhibit a wedge-shaped section 24K.
• the dewatering element 22 has thereby in the rear section 24C a diverging extension in the direction away from the wires 8, 10 and is not in contact with the wires.
• the middle section 24B of the dewatering element 22 may comprise a perforated dewatering element.
• the middle section constitutes a so called dewatering zone (see the arrow in Fig. 1B).
• Perforations in the shape of holes 49 in such a perforated dewatering element 22 may be placed in the beginning of the middle section 24B immediately after the inlet radius of the front section. Further, holes 49 may be placed in the end of the middle section 24B immediately before the wedge- shape 24K of the rear section 24C. Due to the wedge-shape 24K of the rear section 24C, directly after the dewatering zone, in combination with the dewatering control means that allow control of the position of the dewatering element, it is possible to divert fluid and only minimal force is lost to rewetting.
• the holes 49 in the dewatering element 22 are placed at the surface, against the wire, through which holes 49 draining of the white water takes place.
• Fig. 2 schematically shows an overview along a longitudinal section of a twin wire press 2 according to an embodiment of the present invention, comprising a press nip 25 according to the embodiments shown in Fig. 1A-B.
• the twin wire press 2 has a dewatering space 12 with an inlet space 52 in the area at and around a head box 14.
• the fibre suspension to be dewatered is supplied from the head box 14 to the dewatering space 12 limited by a continuous lower wire 8 and a continuous upper wire 10 during movement of the wires 8,10.
• Perforated dewatering elements bear against the wires outside the dewatering space.
• the filtrate flows through the wires 8,10 from the dewatering space and is collected in discharge boxes 18, 16.
• the lower discharge box 18, provided in a lower dewatering table receives the filtrate flowing from the dewatering space through the lower wire 8 and lower dewatering element
• the upper discharge box 16, provided in an upper dewatering table receives the filtrate flowing from the dewatering space through the upper wire 10 and upper dewatering element.
• the twin wire press 2 comprises three lower rolls, a driving roll 100, a control roll 102 and a tension roll 104.
• the above mentioned continuous lower wire 8 runs in a path around the lower rolls 100,102,104.
• the above mentioned upper continuous wire 10 in a path around three upper rolls, a driving roll 106, a control roll
• the twin wire press comprises an arrangement of rolls 4, comprising a press nip 25 according to the present invention.
• a movement of the wires 8,10 takes place when the rolls 100-110 rotate.
• the fibre suspension to be dewatered is supplied to the elongated dewatering space 12 through the head box 14 at the inlet space 52 thereof.
• the fibre suspension is dewatered in the dewatering space 12 during movement of the wires, so that a flow of filtrate is formed from the dewatering space
• a fibre web F is formed between the wires, and an arrangement of rolls 4 is provided after the dewatering table, seen in the direction of movement of the wires, for final pressing and dewatering of the fibre web between the wires, giving the fibre web F the desired dry solids content.
• Dewatering and pressing takes place in a first press nip 25 in the arrangement of rolls by a first dewatering control means 22 having a first dewatering element 24 pressing the formed fibre web F against the first roll 26, or the alternative second dewatering element, via the wires 8,10. Water pressed from the fibre web F by the dewatering element 24 is at least partially drained through the dewatering element 24.
• the arrangement of rolls in the twin wire press comprises more than one press nip 25, as mentioned above, for applying the separate pressing force P.

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• 2009
  • 2009-05-28 EP EP09755135A patent/EP2342380A4/de not_active Withdrawn
  • 2009-05-28 WO PCT/SE2009/000277 patent/WO2009145697A1/en active Application Filing
  • 2009-05-28 CN CN2009801199217A patent/CN102046878A/zh active Pending

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