WO2002002868A1

WO2002002868A1 - Wash press having an oscillating spray arrangement

Info

Publication number: WO2002002868A1
Application number: PCT/SE2001/001505
Authority: WO
Inventors: Axel LÄMÅS; Göran BRÖTTGÅRDH; Bo CLARSTRÖM; Stefan Hansson
Original assignee: Kvaerner Pulping Ab
Priority date: 2000-07-04
Filing date: 2001-06-29
Publication date: 2002-01-10
Also published as: AU2001266535A1; SE517824C2; SE0002516D0; SE0002516L

Abstract

The invention relates to a device for washing and dewatering a fibre pulp suspension, comprising two circular-cylindrical screen members (1) which are arranged to rotate towards each other for the purpose of forming a press nip (2) at least one of which said screen members is hollow, permitting evacuation of liquid radially inwards in the screen member, and is arranged in a trough (7, 8) which partially encloses the jacket (3) of the screen member, with the fibre pulp suspension being supplied between the jacket (3) of the screen member and its trough (7, 8), which is provided with longitudinal seals 5, and in which the device also includes at least one arrangement (6) for scavenging, which arrangement is organized in the area between the nip (2) and the point at which the screen member (1) once again comes into contact with the suspension, with the said arrangement (6) including at least one nozzle (63) for emitting a flat high-pressure jet (64) which is in the main directed towards the jacket surface of the screen member, which nozzle is arranged to oscillate, forwards and backwards, along the axial extent of the screen member (1), along the periphery of the screen member (1) without bearing against the screen member. The invention is characterized by the fact that the flat high-pressure jet (64) has its longest extent at an angle which is less than 30°, preferably less than 15°, and is expediently in the main 0°, relative to the direction of rotation of the screen member and, by means of an oscillating movement out towards the ends of the screen member, flushes and pushes fibre residues away towards the ends of the screen member.

Description

WASH PRESS HAVING AN OSCILLATING SPRAY ARRANGEMENT

TECHNICAL FIELD

The invention relates to a wash press, more precisely to a device for washing and dewatering a fibre pulp suspension, in accordance with the preamble to Patent Claim 1.

STATE OF THE ART

Dewatering of suspensions, such as pulp fibre suspensions, can take place using wash presses which comprise one or more cylindrical, rotatably arranged screen members. The dewatering takes place through the jacket surface, which is frequently provided with a cloth and usually perforated with holes, of the cylindrical screen member, with the screen member being arranged in a trough which partially encircles the jacket of the screen member. The suspension which is to be dewatered is supplied to the trough, with the liquid in suspension passing through the jacket of the rotating screen member at the same time as the solid particles in the suspension form, and develop, a cake or a web on the jacket of the screen member. After the web has come up out of the trough, as a result of the rotation of the screen member, and after the web has been subjected to further dewatering, for example by pressing it in the gap between two cooperating screen members, the web is removed from the jacket, for example by being scraped off the jacket using a scraper (doctor) . After the web has been removed, the jacket of the screen member is relatively free of fibres until this part of the jacket of the screen member comes into contact once again with the suspension in the trough, after which the process is repeated as a result of the rotation of the screen member. However, some fibres, and possibly other substances, will remain on the jacket of the screen member after the web has been removed and could give rise to problems if they were not regularly removed by means of additional cleaning measures. Such a problem is wear and tear of those gaskets between the trough and the jacket surface which are required in modern presses in which the suspension is pressurized in order to increase dewatering efficiency. Another problem is that, inter alia due to the fact that the pulp suspension is kept at a relatively high temperature in order to facilitate the dewatering, any fibres, and possibly other substances, which remain can gradually "burn on" and give rise to depositions and encrustations on and in the screen member. These problems either lead to decreased efficiency or else to the equipment being available to a reduced extent.

These additional cleaning measures usually consist of an organization of arrangements for scavenging, which arrangements, by applying water or process liquids at relatively high pressure, detach those residues which have remained after the web has been removed.

While US 3 969 247, US 4 861 433, US 5 421 176, US 5 667 642 and SE 512 753 describe dewatering/washing equipment which is provided with such scavenging arrangements, they do not go into any detail with regard to the design of these arrangements.

EP 0 454 392 Al describes a device for thickening lime sludge, which device also includes a scavenging arrangement (20, 22) . The description of this patent mentions mobile nozzles which move continuously forwards and backwards axially along the drum.

The expired patent SE 507 502 describes a device for cleaning press rollers, which device is in the form of a scavenging arrangement having at least one nozzle for emitting high pressure jets, with it being possible for the nozzle to be moved forwards and backwards in the axial direction along the periphery of a roller. One of the subclaims mentions that the high pressure jet can be flat and thereby have its longest extent in the direction of movement of the nozzle, i.e. parallel with the axial extent of the roller. In the prior art, pulp presses have conventionally been designed with pulp troughs which only surround the lower part of the press rollers, i.e. up to the axis of the press rollers. In such presses, the scavenging arrangements are organized in a rotational position where fibre residues which have been washed away can fall down vertically towards the open pulp trough. If the pulp trough is not open, use is then made of seals of the type shown in SE,B, 503010, which seal can then allow these pulp residues to pass.

In modern and high-performance wash presses, as are described in SE 512 753, the dewatering efficiency has been increased, firstly by the suspension in the trough having been placed under pressure and secondly by the effective screen area having been increased in such a way that the extent to which the trough surrounds the jacket has been made so large that the distance between the point at which the web is removed from the screen member and the point at which the suspension is supplied to the trough by way of an inlet box is very small. In this connection, an efficient seal is required between the inlet box and the jacket surface in order to prevent (pulp) suspension -which has been supplied from leaking out and rewetting the dewatered pulp web .

With this type of seal, it is not possible to implement scavenging arrangements of the conventional type and rely on loosened fibre residues falling back down into the pulp trough with the aid of gravity. In this connection, there is a risk that fibre residues begin to be deposited up towards the seal, with the fibre residues piling up in considerable quantity if appropriate steps are not taken.

This seal is also susceptible to wear which is caused, inter alia, by residues which remain on the jacket surface after the (pulp) web has been removed, and such damage to this seal is an example of damage which is not satisfactorily solved using scavenging arrangements of the prior art.

The prior art for cleaning screen members in wash presses consequently comprises arrangements for scavenging which detach those residues which remain on the screen member (s) after the web of the suspended substance has been removed, with these loosened fibre residues running off radially and downwards from the screen member towards the pulp trough. If these residues do not become detached in this connection, and are returned to the pulp trough, or alternatively pass through the jacket of the screen member, they then remain on the jacket surface and begin to accumulate towards the sealing strips, if such are present.

BRIEF DESCRIPTION OF THE INVENTION

The¹ object of the invention is to offer a wash press having a scavenging arrangement which, during operation, continuously detaches fibres and residues which remain on the screen member (s) after the web has been removed and also, to a large extent, conducts these fibres and residues away to one or both sides of the screen member (s) with this efficient cleaning decreasing the wear on the equipment and preventing damage to this equipment.

A further aim is also to allow fibre residues to be sluiced efficiently away from the screen member and the sealing strip of the pulp inlet box in wash presses in which the pulp inlet box is placed at the highest point of the screen member and in which the scavenging arrangement of the screen member is organized at this highest point, where it is not possible to make use of the effect of gravity on fibre residues which have been detached by washing in order to let these residues fall directly downwards back into the pulp trough/pulp inlet box.

This object is achieved with a wash press in accordance with the characterizing part of Patent Claim 1.

In this connection, fibre residues which remain after the pulp web has been removed are detached and removed using a scavenging arrangement which comprises at least one nozzle which is arranged such that it is able to execute an oscillating movement, i.e. a forward and return movement, along the axial extent of the screen member. The nozzle is designed such that it is able, using a flat jet which is principally directed towards the jacket surface of the screen member, to apply a scavenging liquid, with the flat jet having its longest extent at an angle which is less than 30°, preferably less than 15°, and which is expediently approx. 0°, relative to the rotational direction of the screen member.

The flat jet should consequently form an angle which is more than 60°, preferably more than 75°, and which is expediently approx. 90°, relative to the extension length of the seal of the pulp trough, on the one hand, but also relative to the direction of at least that part of the oscillating stroke, either the forward or return stroke or both, when the nozzle is simultaneously activated. This thereby creates a "plough" which, in cooperation with the oscillating movement of the nozzle forwards and backwards along the screen member, "ploughs away" the fibre residues from the jacket surface and from the seal of the pulp inlet box and onwards towards the end or ends of the screen member (s), after which the residues can be collected and conveyed away, for example by way of catching outlets. In this connection, the jet is preferably activated only in association with that part of the oscillating movement of the nozzle which 'is in the direction towards the end of the screen member towards which the fibre residues are to be transported. It is also possible to activate the jet only during a part of the oscillating movement which is in the direction towards the end of the screen member towards which the fibre residues are to be transported.

In a preferred embodiment, this "ploughing effect" is amplified by the nozzle additionally being tilted such that the centre of the jet from the nozzle is directed outwards towards the end towards which the fibre residues are to be transported, i.e. in the direction in which the nozzle is conveyed when the jet is activated with the angle of the tilting, radially inwards towards the centre of the screen member, of the centre of the jet from the nozzle being from 20 to 60 degrees, preferably from 30 to 45 degrees, relative to the direction of movement of the nozzle when the jet is activated.

The scavenging arrangement is expediently designed with several nozzles, which are designed as described above and which are located side by side along the axial extent of the screen member, for example by the nozzles being arranged on a pipe which oscillates forwards and backwards along the axial extent of the screen member. In a preferred embodiment, the nozzles are fixed to a pipe, with there being a distance of about 100 mm between each nozzle, and in which the extent of the cleaning stroke corresponds to, or somewhat exceeds, this distance, i.e. > 100 mm. In this connection, the tilting of the nozzles can be such that all the nozzles are pointed in the same direction, for the purpose of discharging fibre residues towards one end of the press, or pointed in different directions, starting from the central section of the pipe, for the purpose of discharging fibre residues to the different ends of the press. In the latter case, the jets from the nozzles can, if so desired, be activated alternately such that the jets from the nozzles which are tilted towards the end of the screen member towards which the oscillating movement is currently directed are activated whereas the others are not.

In this connection, the oscillation movement, and the activation of the jet from the nozzle (s) , can take place continuously, in the above-described manner, or be adapted to the scavenging requirement, for example by means of the oscillation, and the activation, which is connected to it, of the jet from the nozzle (s), taking place intermittently or discontinuously. However, discontinuous activation of the nozzles is preferably only used when it is wished to minimize the quantities of liquid in the process in question or when intermittent activation is fully able to cope with detaching and flushing away fibre residues.

The fibre residues which have been detached and discharged over the end(s) of the jacket of the screen member, together with a part of the flushing water from the nozzle (s), can be collected up in separate catching outlets which are arranged at the end(s) of the screen member. From there, this discharge can be conducted to various sites in the process depending on the fibre content. In order to facilitate the discharge of the fibre residues over the jacket surface and out towards the end(s), it is possible to additionally arrange, axially, along the jacket and bearing against it, a longitudinal element downstream of the flushing device and in the direction of transport of the pulp web. This element, towards which a part of the flat jet from the nozzle (s) is expediently directed, forms, together with the jacket surface, a channel which opens out in the said catching outlet. Instead of such an element, it can be expedient to use an existing machine element, if such is present, for example the seal 5 which extends axially between the jacket surface and the trough or the inlet box of the trough.

Preference is given to using fixed, tilted nozzles on the pipe which is oscillated in the axial direction. Alternatively, it is also possible to use a fixed pipe where, instead, nozzles are rotated around an axis parallel with the direction of rotation of the screen member, which rotation, over an angular deflection of at least 20 - 60 degrees, corresponding to the said tilting of fixed nozzles radially inwards towards the centre of the screen member of the centre of the jet from the nozzle. This embodiment also provides a flattened jet which pushes fibre residues before it and out towards the end or ends of the screen member.

Additional features and aspects, and also advantages, of the invention will be evident from the subsequent patent claims and from the following detailed description of some embodiments of the invention.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows an example of a wash press in accordance with the invention,

Fig. 2 is a detailed perspective view of a wash press in accordance with Fig. 1 comprising a scavenging arrangement,

Fig. 3A is a detailed drawing of the scavenging arrangement, which shows a part of a scavenging pipe and which illustrates the tilting of the scavenging nozzles,

Fig. 3B is a section from Fig 3A,

Fig. 4 is an alternative embodiment with swivelling nozzles

Fig. 5 is an alternative in which half the nozzles are in each case angled towards their own end of the screen member. DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS OF THE INVENTION

The preferred embodiment of the device according to the invention is illustrated here by means of a wash press for paper pulp in accordance with Fig. 1, which wash press comprises two circular-cylindrical screen members 1, with the jackets 3 on the screen members being hollow and permitting evacuation of liquid radially inwards in these jackets. The two screen members form a press nip 2 between themselves and are arranged to rotate towards each other with, as seen from the short end, the right screen member rotating clockwise and the left screen member rotating counter clockwise.

A pulp inlet box 4 is arranged in association with each screen member 1 for supplying pulp to the trough 7. At the rear edge of the trough 7, there is arranged a longitudinal seal 5 which bears against the jacket 3 of the screen member and which prevents liquid running from the incoming pulp suspension against the direction of rotation and rewetting outgoing pulp which has already been dewatered and pressed.

Above the nip 2, there is arranged a stripper and conveyor worm 20, which strips off the washed, dewatered and pressed fibre pulp web and transports it away for further treatment in the process. As an alternative, or a supplement, it is also possible to use a doctor for removing the fibre pulp web from the jacket 3.

A scavenging arrangement 6 is organized between the device 20 and the seal 5.

Fig. 2 is a detailed perspective view which shows a part of the detaching and discharging device 20 for the pulp web, an oscillating scavenging pipe 61, arranged along the jacket of the screen member 1, and a catching outlet 65.

Fig. 3A is a detailed view which shows the oscillating scavenging pipe 61 with one or more bifurcations 62 to which nozzles 63 can be connected. The bifurcations 62, which are arranged side by side along the scavenging pipe 61, form an angle _α with this pipe and, in this preferred embodiment, have an angle of 45 degrees relative to the scavenging pipe 61, with the said bifurcations being directed towards the end of the screen member 1 towards which the fibre residues are to be discharged.

Fig. 3B shows the jet 64 from a nozzle 63, with the said jet 64 having its longest extent parallel with the direction of rotation on the screen member and being in the main directed towards the jacket 3 on the screen member 1.

During operation, a paper pulp having a concentration of 1-12% is conducted into the gap 19 via the pulp inlet box . The paper pulp then accompanies the rotation of the screen member, in the gap 19 between the perforated jacket surface 3 and the walls of the trough 7, 8, with the paper pulp being dewatered by liquid passing through the jacket surface 3. At the washing zone 18, washing liquid is introduced into the fibre pulp web, with washing of the web then taking place. After that, the fibre pulp web is dewatered, by being pressed in the nip 2 to a concentration which is approx. 5-20 times higher than the concentration of the incoming paper pulp. The fibre pulp is stripped from the jacket 3 and conveyed away from the device with the aid of the stripper and the conveyor worm 20.

Fibre residues which remain on the jacket 3 after the pulp web has been removed with the device 20 are detached and removed using a scavenging arrangement 6 which includes nozzles 63 which are arranged such that they are able to execute an oscillating movement, i.e. a forward and return movement, along the axial extent of the screen member. The nozzles are designed such that they apply a scavenging liquid, with flat jets 64 which are directed towards the jacket surface 3 of the screen member and partially towards the seal 5, with the flat jets 64 having their longest extent in the main parallel with the direction of rotation of the screen member 1. As a result of the oscillating movement of the nozzles 63 forwards and backwards along the screen member 1, the fibre residues are flushed, together with a part of the flushing water, away from the jacket surface 3 and out towards the end of the screen member 1 in the channel which is formed between the jacket surface 3 and the seal 5 and are caught in the catching outlet 65. In certain cases, the jets 64 from the nozzles 63 can only be activated in that part of the oscillating movement of the nozzles 63 which is in the direction towards the end of the screen member 1 towards which the fibre residues are to be transported.

In addition, the nozzles 63, and as a result the jets 64, are tilted radially towards the centre of the screen member in order to amplify the discharge of fibre residues towards the end such that the centre of the jet 64 from the nozzle 63 is directed outwards towards the end towards which the fibre residues are to be transported, i.e. in the direction in which the nozzle is conveyed when the jet is activated, with the angle of the tilting of the centre of the jet from the nozzle being 45 degrees relative to the direction of movement of the nozzle when the jet is activated.

Figure 4 shows the variant in which, instead of being fixedly mounted on the oscillating distribution pipe 61, the nozzle can be rotated around an axis 70, such that the flat jet sweeps over the angular area _β. In certain applications, the jet can be activated only in association with the movement from the position indicated by the dashed line up towards the position for the nozzle 62 indicated by the unbroken line.

In a variant of the above embodiment, the nozzles 63 are tilted in different directions, see Figure 5, starting from the centre of the pipe, for the purpose of discharging fibre residues to their respective ends of the press. The central axis of the screen member is indicated by the number 71. The figure shows the distribution pipe 61 with its scavenging flat jets directed towards their respective ends of the screen member 1. In the latter case, it is possible, in certain cases, for the jets from the nozzles to be activated alternately such that the jets from the nozzles which are tilted towards the end of the screen member towards which the oscillating movement is currently directed are activated whereas the other jets are not. When the distribution pipe 61 is displaced towards the right in Figure 5, it is only the ten nozzles to the right of the central section which are activated, and when the distribution pipe is displaced towards the left in the figure, it is the other ten nozzles, to the left of the central section, which are then activated. At the same time, a catching outlet is arranged at each end of each screen member in the wash press .

The oscillation movement, and the activation of the jet from the nozzle (s), can preferably take place continuously in the above-described manner. If it is desired to minimize the quantities of water, or to adjust them to a reduced scavenging requirement, this can then take place by the oscillation and the activation, which is connected thereto, of the jet from the nozzle (s) taking place intermittently or discontinuously.

Claims

PATENT CLAIMS

1. Device for washing and dewatering a fibre pulp suspension, comprising two circular-cylindrical screen members (1) which are arranged to rotate towards each other for the purpose of forming a press nip (2) at least one of which said screen members is hollow, permitting evacuation of liquid radially inwards in the screen member, and is arranged in a trough (7, 8) which partially encloses the jacket (3) of the screen member, with the fibre pulp suspension being supplied between the jacket (3) of the screen member and its trough (7, 8) , which is provided with longitudinal seals 5, and in which the device also includes at least one arrangement

(6) for scavenging, which arrangement is organized in the area between the nip (2) and the point at which the screen member (1) once again comes into contact with the suspension, with the said arrangement (6) including at least one nozzle (63) for emitting a flat high- pressure jet (64) which is in the main directed towards the jacket surface of the screen member, which nozzle is arranged to oscillate, forwards and backwards, along the axial extent of the screen member (1) , along the periphery of the screen member (1) without bearing against the screen member, c h a r a c t e r i z e d i n that the flat high- pressure jet (64) has its longest extent parallel with an angle which is less than 30°, preferably less than 15°, and expediently is in the main 0°, relative to the direction of rotation of the screen member, with the jet (64) preferably only being activated during that part of the oscillating movement which is directed towards the end of the screen member (1) towards which the fibre residues are to be discharged.

2. Device according to Claim 1, c h a r a c t e r i z e d i n that the nozzle (63) is fixedly arranged on a pipe which oscillates in the axial direction, with the nozzle being arranged such that the centre of the jet from the nozzle is tilted in towards the central axis (71) of the screen member (1) and exhibits an angle of 20 to 60 degrees, preferably of 30 to 45 degrees, relative to the axial extent of the screen member (1) .

3. Device according to Claim 1, c h a r a c t e r i z e d i n that the nozzle (63) is rotatably arranged on a fixed pipe, in connection with which it can be rotated around an axle joint (70) parallel to the direction of rotation of the screen member, with the centre of the jet from the nozzle being tilted in towards the central axis (71) of the screen member (1) and sweeping over an angular area (p) corresponding to at least 20-60 degrees relative to the axial extent of the screen member (1) .

4. Device according to Claim 2 or 3, c h a r a c t e r i z e d i n that several nozzles (63) are arranged along a scavenging pipe (61) and in that all the nozzles (63) are arranged such that they direct the jets (64) towards one of the ends of the screen member, with the jets (64) preferably at least being activated during that part of the oscillating movement of the nozzles (63) which is in the direction towards the said end.

5. Device according to Claim 2 or 3, c h a r a c t e r i z e d i n that several nozzles

(63) are arranged along a scavenging pipe (61) and in that one half of the nozzles (63) are directed towards one end of the screen member and the other half of the nozzles (63) are directed towards the other end, starting from the centre of the scavenging pipe (61), in such a way that they are directed towards the nearest end of the screen member (1), with the jets

(64) from the respective nozzles (63) preferably being activated alternately such that the jets from the nozzles which are directed towards the end of the screen member towards which the oscillating movement is currently directed are activated whereas the others are not .

6. Device according to any one of the preceding claims, c h a r a c t e r i z e d i n that the nozzles 63 are arranged such that the flat jets (64) from the nozzles partly flush over towards the seal(s) (5) of the pulp trough (7,8) and partly flush over the surface of the screen member.

7. Device according to any one of the preceding claims, c h a r a c t e r i z e d i n that catching outlets are arranged at the end(s) of the screen member (s) for the purpose of collecting the fibre residues and a part of the flushing water which is discharged over the end (s ) .

8. Device according to any one of the preceding claims, c h a r a c t e r i z e d i n that the pulp troughs are arranged in the area of the highest point of the screen member and in that the nozzles are arranged to act against the screen member within an angular area of 5-20 degrees seen from the highest point of the screen member.