DISTRIBUTION UNIT IN AN INLET BOX FOR A DEWATERING PRESS

Abstract

A distribution unit for adding a fiber suspension to an inlet space in a dewatering press is disclosed. The distribution unit comprises a distribution housing, which forms at least one distribution slit intended to be connected to the inlet space of the dewatering press, and at least one inlet member for adding the fiber suspension to the distribution slit. The distribution housing is provided with at least one opening to the distribution slit and a matching hatch for sealing the opening. The hatch is hinged to the distribution housing so that it is pivotable relative to the distribution housing between a first position and a second position. An inlet box is also disclosed comprising a number of the distribution units.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 U.S.C. §371 of International Application No. PCT/SE2008/000143 filed Feb. 21, 2008, published in English, which claims priority from Swedish Application No. 0700530-9 filed Mar. 1, 2007, all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a distribution unit for adding a fiber suspension to an inlet space of a dewatering press. More particularly, the present invention also relates to an inlet box comprising one or more of these distribution units. Still more particularly, the present invention relates to a twin-wire press with the inlet box and a use of the distribution unit or inlet box for a twin-wire press.

BACKGROUND OF THE INVENTION

Dewatering presses for dewatering of fiber suspensions and forming a continuous web thereof are previously known. One example of a known dewatering press is a twin-wire press. Dewatering of the pulp is usually carried out from an inlet pulp concentration of from 3 to 8 percent by weight to an outlet pulp concentration of from 30 to 50 percent by weight. According to the state of the art, such twin-wire presses comprises lower rolls, an endless lower wire running in a path around the lower rolls, upper rolls, and an endless upper wire running in a path around the upper rolls. The two wires co-operate with each other along dewatering sections of these paths, in which the wires form a wedge-shaped dewatering space for the fiber suspension between each other. During displacement of the wires along these dewatering sections, the wires thus successively compress the fiber suspension in the wedge-shaped space, whereby the fiber suspension is initially pressed and dewatered and formed to a continuous fiber web between the wires.

An inlet box provides for supply of fiber suspension to the wedge-shaped dewatering space between the wires. The known twin-wire presses further comprise two dewatering tables supporting the respective wire in the dewatering sections of the path, such that the wedge-shaped dewatering space is formed between the wires, and a roll arrangement situated after the dewatering tables, as seen in the direction of movement of the wires, for finally pressing and dewatering of the fiber web between the wires, so that the fiber web will obtain a desired dryness. Alongside the longitudinal direction of the wires, in the wedge-shaped dewatering space, there are perforated dewatering elements that are arranged against the wires outside the dewatering space. Formed filtrate flows through the wires and the perforated dewatering elements and is led away to upper and lower outlet boxes, respectively, arranged at the dewatering tables. The upper and lower outlet boxes may be divided into several chambers whereby a filtrate that flows through the upper and lower dewatering elements may be divided into partial filtrate in two or more chambers in the respective outlet box.

In the traditional twin-wire press the geometry for the inlet box, for adding of the suspension to the wedge-shaped dewatering space between the wires, is very difficult to set to obtain the correct and desired suspension flow. This geometry is carefully tested through numerous tests and trial-runs for a long period of time before the twin-wire press is placed in production. The geometry for the inlet box is hence fixed.

The fiber suspension is fed from a container, though gravity or with a pump, through inlet pipes into a distribution unit at the inlet box. When entering into the distribution unit the fiber suspension meets a first distribution sheet, whereby the fiber suspension is distributed over the entire width of the distribution unit in a slit and the fiber suspension is thereafter re-linked around the distribution sheet to the next slit and on to an outlet for further feeding to the wedge-shaped dewatering space between the wires.

Different kinds of disturbances to the production can occur in this process, whereby problems arise with the inlet box. In the inlet box formation of so called plugs, consisting of fiber suspension that is locally thickened resulting in the fiber suspension standing still, can occur, resulting in the inlet box having to be opened for cleaning. Malfunction of the propelling motor, system errors, or an emergency halting of the machine, can also led to occasional problems with the inlet box, which means that it has to be opened for control and occasional repair. It also happens that the inlet box needs to be opened for performing normal maintenance on the inlet box.

A traditional inlet box consists of a number of metal sheets which are joined with a large number of bolted joints. Opening the inlet box to make room for cleaning, or to perform repairs on the inside of the inlet box, such as the slits, is time consuming and complicated. Large parts of the inlet box have to be disassembled. The straightness of the metal sheets, and the tolerances in general for the slits, are precise, in order to obtain as good a distribution of the fiber suspension as possible. Since the slits, which are formed from inner metal sheets in the inlet box, have extensive spreading over large surfaces with few supports, the load on the slit sheets is relatively large. The slits, which are formed from the metal sheets, are therefore very sensitive to rapid increases in pressure. It is enough with a few bars of overpressure to damage the metal sheets and make unacceptable changes in the slit tolerances. If the pressure gets far too high the inlet box could be damaged and in worst case it can collapse.

A conventional inlet box comprises one or more distribution units for adding a fiber suspension to an inlet space in a dewatering press. Since the tolerances of the slits of each distribution unit are carefully determined, usually multiple distribution units are required for one inlet box in a dewatering press, since otherwise the surfaces become far too large, and it is difficult to maintain the set tolerances in the slits.

In a conventional inlet box, comprising one or more distribution units, it is known to use pressure sensors, placed inside of respective distribution unit in the inlet box, which when sensing an excess pressure sends a signal to the control system of the press for shutting down the feeding of the fiber suspension to the inlet box. However such a shutdown happens by means of the control system with some delay. It is also known that there are explosive members connected to the control system, which are mounted in the distribution units in the inlet box so that the bolted joints can be blasted and the joined metal sheets separated, at a signal from the control system, so that the increased pressure inside the distribution units in the inlet box can be removed, to thereby prevent permanent damage to the inner parts of the distribution units of the inlet box. Naturally, there some damage to the bolted joints and outer metal sheets which require extensive repairs. Maintenance, control and repair of a conventional distribution unit or inlet box results in long stoppages of production, which means lost production time, and hence an increased cost.

The purpose of the present invention is to at least partially eliminate the disadvantages associated with the state of the art mentioned above. A general purpose in accordance with the present invention is to achieve an improved distribution unit and an inlet box respectively, comprising one or more distribution units. More precisely, one purpose is to achieve a distribution unit and an inlet box with a longer life span and/or to achieve simpler and faster maintenance in a dewatering press, such as a twin-wire press. Yet another purpose is, to a larger extent, to be able to even out the increased pressures in the distribution unit in the inlet box or to stop the feeding of the fiber suspension in sufficient time before the risk of damage to the distribution unit or the inlet box arises. Furthermore, another purpose is to reduce the cost of repairs, control and maintenance of an inlet box for a dewatering press such as a twin-wire press.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other objects have now been realized by the invention of a distribution unit for adding a fiber suspension to an inlet space in a dewatering press, the distribution unit comprising a distribution housing forming at least one distribution slit intended to be connected to the inlet space and at least one inlet member for providing the fiber suspension to the at least one distribution slit, whereby the fiber suspension can pass through the at least one distribution slit while spreading therein, the distribution housing further including at least one opening into the at least one distribution slit and a hatch for sealing the at least one opening, the hatch hinged to the distribution housing whereby the hatch is pivotable with respect to the distribution housing between a first position in which the hatch seals the at least one opening and a second position in which the hatch exposes the at least opening, and pressure means for allowing the hatch to be moved at least partially towards the second position based upon the pressure in the at least one distribution slit exceeding a predetermined pressure value. Preferably, the pressure means comprises at least one hydraulic cylinder for moving the hatch between the first and second positions. In a preferred embodiment, the predetermined pressure value in the at least one hydraulic cylinder is adapted to substantially correspond to the load created by the maximum allowed pressure in the at least one distribution slit.

In accordance with one embodiment of the present invention, the at least one hydraulic cylinder includes a pressure limiting device.

In accordance with another embodiment of the present invention, an inlet box is provided for adding a fiber suspension to an inlet space of a dewatering press comprising at least one distribution unit as set forth above. In a preferred embodiment, the inlet box comprises a plurality of the distribution units, a common inlet pipe for feeding the fiber suspension to the inlet members and the distribution slits in the plurality of distribution units, and including a pressure sensor arranged in the common inlet pipe.

In accordance with another embodiment of the present invention, a twin-wire press is provided for dewatering a fiber suspension comprising a plurality of lower rolls, an endless lower wire around the plurality of lower rolls, a plurality of upper rolls, an endless upper wire around the plurality of upper rolls, and an inlet box as set forth above.

the objects of the present invention are achieved with a distribution unit for adding of a fiber suspension to an inlet space in a dewatering press, in accordance with the present invention, which distribution unit comprises a distribution housing, which forms at least one distribution slit. The distribution slit is intended to be coupled to the inlet space of the dewatering press. The inlet box comprise at least one inlet member for adding a fiber suspension to the distribution slit, so that the fiber suspension passes through the distribution slit while spreading in the slit. The distribution housing is equipped with at least one opening to the distribution slit and a hatch belonging to the opening for shutting thereof. The hatch is hinged to the distribution housing in such a way so that it is pivotable relative to the distribution housing between a first position, in which the hatch seals the opening, and a second position, in which the hatch exposes the opening. The distribution unit is arranged to enable the hatch to move at least somewhat towards an open position under the influence of a pressure exceeding a predetermined value, in the distribution slit.

Repairs and inspection therefore become less complicated in comparison to the construction in accordance with the traditional distribution units in an inlet box. In accordance with the present invention the costs of repairs and inspection are reduced, as well as assembling and replacing themselves since the duration of production halts can now be considerably reduced, in comparison to the traditionally used distribution units in an inlet box. Damages to the distribution unit and the inlet box, respectively, can be avoided to a large extent.

Thanks to the fact that the distribution unit is arranged to enable movement of the hatch to at least a somewhat more open position under the influence of a pressure, exceeding a predetermined value, in the distribution slit, the hatch can consequently be automatically opened in case of a increased pressure inside the distribution unit, whereby damages to, among other things, the distribution slits in the distribution unit can be minimized to a large extent.

According to one embodiment of the present invention, a hydraulic cylinder is arranged to move the hatch between the first and second positions.

The pressure in the hydraulic cylinder can be adapted to essentially correspond to the load that the pressure by the maximum allowed pressure in the distribution slit creates.

The present invention also relates to an inlet box for adding a fiber suspension to an inlet space in a dewatering press, comprising one or more distribution units, which have been described above in accordance with the present invention.

The present invention also relates to the use of a distribution unit or an inlet box, which have been described above in accordance with the present invention, for a twin-wire press.

The present invention also relates to twin-wire press comprising an inlet box, which have been described above according to the present invention.

Additional preferred features, advantages and preferred embodiments according to the invention are evident from the dependent claims, and also from the following description of examples of embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention shall now be described in more detail with reference to the following detailed description, which in turn refers to the accompanying drawings, without restricted interpretation of the invention thereof, where:

FIG. 1A is a side, elevational, partially schematic cross-sectional view of a distribution unit comprising a hatch, according to one embodiment of the present invention, in a first position with the hatch closed;

FIG. 1B is a side, elevational, partially schematic cross-sectional view of the distribution unit shown in FIG. 1A, in a second position with the hatch open;

FIG. 1C is a side, perspective, partial view of the distribution unit according to FIGS. 1A-B, with the hatch in the open position;

FIG. 1D is a front, perspective, partially schematic view of a part of an inlet box, comprising a plurality of distribution units with a respective hatch, according to the distribution unit shown in FIGS. 1A through C, at an inlet part of a dewatering press; and

FIG. 2 is a side, elevational, schematic cross-sectional view of a twin-wire press according to an embodiment of the present invention, that can comprise the inlet box with the embodiment shown in FIG. 1D.

DETAILED DESCRIPTION

Turning to the Figures, in which like reference numerals refer to like elements thereof, in FIGS. 1A through C the distribution unit 1 is shown according to one embodiment of the present invention. The distribution unit 1 comprises a distribution housing 2 that forms at least a first distribution slit 4 and a second distribution slit 4′. The distribution unit 1 comprise at least one inlet member 6 for adding of fiber suspension to the distribution slit. The distribution housing 2 comprises an outlet opening 5 through which the fiber suspension passes after passage through the distribution slit, 4, 4′. The fiber suspension passes through the distribution slit while spreading in the slit. The distribution housing 2 is equipped with at least one opening 8 to the distribution slit, 4, 4′, and a matching hatch 10 for sealing the opening 8. The hatch 10 is hinged to the distribution housing 2, by means of a first pivot 11, so that the hatch is pivotable relative to the distribution housing 2 between a first position P1, in which the hatch 10 seals the opening 8, and a second position P2, in which the hatch 10 exposes the opening 8. Consequently, easier and faster maintenance can now be achieved in a dewatering press, such as a twin-wire press. Furthermore, the increased pressures in the distribution unit 1 can, to a large extent, be evened out. Feeding of the fiber suspension 1 can also be aborted well in advance of the time when the risk of damage to the distribution unit arises. This can take place by the hatch 10 automatically opening, at least partially, at a too large pressure inside the distribution unit 1, and if it is decided, by the process control system or an operator, that there is risk of damage to the distribution unit 1 if running is continued. Feeding of the fiber suspension is then aborted. A pressure which affects the opening of the hatch should be above a predetermined value, in the distribution slit 4, 4′, before the hatch can automatically be opened.

The distribution unit 1 can comprise at least one hydraulic cylinder 12, arranged to move the hatch 10 between these first and second positions, P1, P2. The hydraulic cylinder can be arranged in front of the front end of the hatch 13. The cylinder 14 of the hydraulic cylinder 12 is preferably arranged with respect to the distribution unit 1, at the underside 15 (see FIG. 1D) of the distribution unit. The outer end 16 of the piston bar 18 of the hydraulic cylinder 12 is hinged to the hatch by a second pivot 20. As is shown in FIGS. 1A-D, a link arm 22 can be fixedly fastened to the top of the hatch 24. The link arm 22 is, at its first end 26, hinged to the distribution housing 2 at the first pivot 11, and at the second end 28 the link arm 22 is arranged to the piston bar 18. As illustrated in FIGS. 1A-D, preferably two hydraulic cylinders 12 are arranged at a hatch 10 to move the hatch between the positions P1, P2.

The pressure that is provided by the hydraulic fluid, such as oil, in the hydraulic cylinder 12 can be adapted to essentially correspond to the load that the maximum allowed pressure in the distribution slit, 4, 4′, creates. Calculation of the maximum allowed pressure in the distribution slits, 4, 4′, of the distribution units 1, with regard to a certain safety margin, can preferably be done at the construction, installation or assembly of the distribution units 1. An inlet box 30 preferably comprises several distribution units 1. The pressure in the distribution slits, 4, 4′, can preferably be measured with a pressure sensor arranged in a common inlet pipe (not shown), for the addition of fiber suspension to the distribution slits, 4, 4′, at the distribution units 1, to which inlet pipe all of the inlet members 6 are connected. The hydraulic cylinder 12 can be provided with a pressure limiting member, such as a non-return valve. The pressure in the hydraulic cylinder 12 can also be measured using a manometer.

FIG. 1C shows a distribution unit 1 comprising the hatch 10. As is clear from FIG. 1D, an inlet box 30 is shown, according to one embodiment of the present invention, with a number of distribution units 1 according to FIG. 1A-C, comprising a plurality of hatches 10. The inlet box 30 is shown in FIG. 1D is arranged in a dewatering press, such as a conventional twin-wire press 50. The twin-wire press 50 shows a dewatering space (not shown in FIG. 1D), an endless lower wire 54 and an endless upper wire 56. The dewatering space has en inlet space 52, situated at and around the inlet box 30. The distribution slit 4, 4′ of respective distribution unit 1 at the inlet box 30 is intended to be connected to the inlet space 52 of the dewatering press and the inlet box 30 is hence arranged for adding a fiber suspension to the inlet space 52 of the twin-wire press 50. Again, with reference to FIGS. 1A-C, the fiber suspension is added through the distribution slit, 4, 4′, and de-linking takes place under spreading in at least one distribution slit 4 in the distribution housing 2. The fiber suspension, after passage through the distribution slit, 4, 4′, passes through the outlet opening 5 at the distribution housing 2 to the inlet space in the dewatering press.

FIG. 2 shows schematically in an overview a longitudinal cross-section through a conventional twin-wire press 50 according to an embodiment of the present invention which can comprise the inlet box 30 with a plurality of distribution units 1 according to the embodiments shown in FIGS. 1A-D. Corresponding conventional features and parts are denominated with the same reference numbers for the twin-wire press 50 shown in FIG. 2 as for the distribution unit 1 and the inlet box 30, respectively, with the embodiments according to the present invention shown in FIGS. 1A-D.

The conventional twin-wire press 50 shows a dewatering space 58 with an inlet space 52 in the area at and around the inlet box 30. The fiber suspension to be dewatered is added from the inlet box 30 to the dewatering space 58 limited between the endless lower wire 54 and the endless upper wire 56 under movement of the wires, 54 and 56. Perforated dewatering elements (not shown) have contact with the wires outside of the dewatering space. The filtrate flows through the wires, 54 and 56, from the dewatering space and is collected in outlet boxes, 60 and 62. The lower outlet box 60, arranged in a lower dewatering table, receives filtrate that flows from the dewatering space through the lower wire 54 and lower dewatering element, while the upper outlet box 62, arranged in an upper dewatering table, receives filtrate that flows from the dewatering space through the upper wire 56 and upper dewatering element.

The twin-wire press 50 comprises three lower rolls, one drive roll 100, one control roll 102 and one tension roll 104. The endless lower wire 54 runs in a path around the lower rolls, 100, 102, and 104. In a corresponding manner, the endless upper wire 56 runs in a path around three upper rolls, one drive roll 106, one control roll 108 and one tension roll 110. The upper outlet box 62 in the upper dewatering table that supports the upper wire 56, and the lower outlet box 60 in the lower dewatering table, that supports the lower wire 54, forms the dewatering space 58 between the wires, 54 and 56. The twin-wire press comprises one common roll arrangement 112 according to the state of the art.

In operation of the twin-wire press 50 according to FIG. 2, the transportation of the wires, 54 and 56, takes place under rotation of the rolls, 100-110. The fiber suspension to be dewatered is fed to the oblong dewatering space 58 through the inlet box 30 at the inlet space 52 thereof. The fiber suspension is dewatered in the dewatering space 58 under movement of the wires, so that a filtrate flows from the dewatering space 58 through the wires, 54 and 56, and the perforated dewatering elements are formed. The filtrate that flows from the dewatering space through the wires is collected in the outlet boxes, 60 and 62.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims

1-8. (canceled)

9. A distribution unit for adding a fiber suspension to an inlet space in a dewatering press, said distribution unit comprising a distribution housing forming at least one distribution slit intended to be connected to said inlet space and at least one inlet member for providing said fiber suspension to said at least one distribution slit, whereby said fiber suspension can pass through said at least one distribution slit while spreading therein, said distribution housing further including at least one opening into said at least one distribution slit and a hatch for sealing said at least one opening, said hatch hinged to said distribution housing whereby said hatch is pivotable with respect to said distribution housing between a first position in which said hatch seals said at least one opening and a second position in which said hatch exposes said at least opening, and pressure means for allowing said hatch to be moved at least partially towards said second position based upon the pressure in said at least one distribution slit exceeding a predetermined pressure value.

10. The distribution unit according to claim 9 wherein said pressure means comprises at least one hydraulic cylinder for moving said hatch between said first and second positions.

11. The distribution unit according to claim 10 wherein said predetermined pressure value in said at least one hydraulic cylinder is adapted to substantially correspond to the load created by the maximum allowed pressure in said at least one distribution slit.

12. The distribution unit according to claim 10 wherein said at least one hydraulic cylinder includes a pressure limiting device.

13. An inlet box for adding a fiber suspension to an inlet space of a dewatering press comprising at least one distribution unit according to claim 9.

14. The inlet box according to claim 13 comprising a plurality of said distribution units, a common inlet pipe for feeding said fiber suspension to said inlet members and said distribution slits in said plurality of distribution units, and including a pressure sensor arranged in said common inlet pipe.

15. A twin-wire press for dewatering a fiber suspension comprising a plurality of lower rolls, an endless lower wire around said plurality of lower rolls, a plurality of upper rolls, an endless upper wire around said plurality of upper rolls, and an inlet box according to claim 5.