SE546043C2 - Apparatus for washing cellulose pulp comprising a liquid distributor - Google Patents

Abstract

A liquid distributor (110) in an apparatus for washing cellulose pulp, the liquid distributor comprising a plurality of inlet orifices (111a-b) distributed along a longitudinal direction of the liquid distributor. Each inlet orifice is provided with flow directing means (112) forming a slot for each inlet orifice, the slot having a tangential opening (114) facing in a tangential direction of the press roll, the opening being arranged adjacent the chamber wall (105) to direct the flow along a chamber wall of the apparatus. The flow directing means of at least two adjacent inlet orifices may form longitudinally adjacent slots being separated by means of a separating wall. Alternatively, the flow directing means (112) are provided with one or more lateral openings (121) between their slots, the one or more lateral openings having an overall effective flow area which is less than twice the effective flow area of each tangential opening.

Description

TECHNICAL FIELD The invention relates to liquid distributors for distributing washing liquid in an apparatus for washing cellulose pulp, and an apparatus for washing cellulose pulp comprising such a liquid distributor.

BACKG ROUND Apparatuses for washing and/or dewatering of cellulose pulp are known in the art. l\/lany different types of washing apparatuses are available, some of which are based on press washing and comprise means for pressing the pulp to remove liquid.

The twin-roll press is a well-known type of such a washing and dewatering apparatus, which is provided with two counter-rotating rolls with perforated outer surfaces. A web of pulp is formed on the respective rolls and is transported in the direction of rotation in a vat partially surrounding the rolls, to the so-called press nip between the rolls. The liquid removed from the pulp, i.e. the filtrate, passes through the perforated roll surface in a radial inwards direction and is led to the ends of the press roll, where it is output. Washing liquid or other treatment liquid may be supplied to the pulp web through inlets in the vat. The twin-roll press uses displacement washing, where dirty liquid (liquor) in the pulp is replaced by cleaner wash liquid added to the vat, and pressing, and where the dirty liquid is pressed (squeezed) out from the pulp, in particular at the press nip.

EP2620544 discloses a twin roll press comprising first and second movable slide plates arranged in the vat, which slide plates directs the pulp suspension along the outer drum surface. Slots for introducing washing liquid in a direction of rotation (tangential direction) are formed between the first and second slide plates and between the second slide plate and the vat wall. Such slots may result in uneven washing however, where the washing result varies along the axial length of the press.

SUMMARY An object of the invention is to provide a liquid distributor and an apparatus for washing comprising such a liquid distributor which provide a more even washing result. A further object is to provide such a liquid distributor and apparatus of a robust design. A further object is to provide a liquid distributor and apparats which allows for convenient cleaning and maintenance.

These and other objects are achieved by the present invention by means of a liquid distributor and an apparatus according to the independent claims. Preferred embodiments are defined in the dependent claims.

According to a first aspect of the invention, there is provided a liquid distributor in an apparatus for washing cellulose pulp, which apparatus comprises at least one rotatable press roll having a permeable outer surface, and at least one corresponding chamber wall at least partly enclosing the roll to define a pulp treatment chamber between said roll and said wall. The liquid distributor is adapted to distribute liquid into said pulp treatment chamber. The liquid distributor comprises a plurality of inlet orifices distributed along a longitudinal direction of the liquid distributor, which longitudinal direction is substantially parallel with the axis of rotation of the roll when the liquid distributor is mounted on the apparatus for washing cellulose pulp. Each inlet orifice is provided with flow directing means forming a slot for each inlet orifice, said slot having a substantially tangential opening facing in a tangential direction of the press roll, said opening being arranged adjacent said chamber wall to direct said flow along said chamber wall. The flow directing means of at least two adjacent inlet orifices, or of each inlet orifice, either form longitudinally adjacent slots being separated by means of separating wall(s) or are provided with one or more lateral openings between adjacent slots, the one or more lateral openings having an overall effective flow area which is less than four times, or less than three times, preferably less than twice the effective flow area of each tangential opening. Alternatively, the one or more lateral openings may have an overall effective flow area which is less than the effective flow area of each tangential opening. ln other words, the flow directing means of each inlet orifice forms a slot having an opening facing in a substantial tangential direction. The liquid distributor is configured such that when mounted in the apparatus for washing cellulose pulp, the openings of the slots are arranged adjacent the chamber wall, for instance between two chamber wall portions. Alternatively, the liquid distributor may form a chamber wall portion with the slot openings defined therein. Alternatively, the liquid distributor may form a chamber wall portion arranged adjacent another chamber wall portion with the slot openings defined therebetween. The flow directing means of at least two adjacent inlet orifices, or each inlet orifice, may form longitudinally adjacent slots being separated by means of a separating wall in the sense that individual slots are formed for each inlet orifice such that all liquid flow from the respective inlet orifice is redirected out through the tangentially facing opening of the corresponding slot. Alternatively, the flow directing means of at least two adjacent inlet orifices, or the flow directing means of each adjacent pair of inlet orifices, are provided with one or more lateral openings between their slots, i.e. at least two, or each, slot is in fluid communication with its adjacent slot(s) via one or more lateral openings. The one or more lateral openings between two adjacent flow directing means/slots may have an overall effective flow area which is less than twice the effective flow area of each corresponding tangential opening.

The invention is based on the insight that the uneven washing of the prior art is due to washing liquid flowing in the axial/longitudinal direction away from areas having high vat pressure to areas having lower vat pressure. The invention is further based on the insight that a substantially more even washing may be achieved by introducing the washing liquid via a plurality of inlet orifices distributed along the axial/longitudinal direction of the drum, each being provided with flow directing means which forms a slot which not only directs the flow tangentially, but also limits the flow in the axial/longitudinal direction, and preferably prevents axial/longitudinal flow altogether. The invention is further based on the insight that optimal washing performance may be achieved by the flow directing means having an effective flow area in the axial/longitudinal direction between adjacent slots which is less than twice the effective flow area in the tangential direction. lt is understood that the axial, longitudinal or lateral direction refers to a direction in parallel with the axis of rotation of the press roll. lt is furthermore understood that the tangential direction refers to the tangential direction of the roll, which may also be referred to as the direction of rotation of the roll. ln embodiments, the flow directing means of at least two adjacent inlet orifices, or each inlet orifice, form longitudinally adjacent slots being separated along a portion of the tangential length of the slots by means of a separating wall such as to form the one lateral opening. ln embodiments, the separating wall between the at least two longitudinally adjacent slots extends along the whole tangential length of the slots. Separating walls may be provided between each pair of longitudinally adjacent slots, such as to form individual slots for each inlet orifice, which separating walls extend along the whole tangential length of the slots. ln embodiments, the flow directing means of at least two adjacent inlet orifices are formed by a flow directing device comprising a substantially tangentially extending flow redirecting wall and said separating wall. The separating wall not only limits the flow in the axial/longitudinal direction but also makes the flow directing device more robust since it adds support in the radial direction to the flow directing wall. The separating wall(s) may be formed such that each slot has an expanding cross-section along at least part of its extension in a liquid flow direction. This may be advantageous since the liquid flow is effectively directed fon/vards. ln embodiments, the slots of at least two adjacent, or all, inlet orifices are formed immediately adjacent each other to form a common slot, such as to form said one lateral opening along the whole tangential length of said slots. The common slot may be formed by a flow directing device comprising a substantially tangentially extending flow redirecting wall which may be substantially planar. ln embodiments, the flow redirecting wall may be releasably attached to the chamber wall. This may be advantageous since the slots can be conveniently cleaned. ln embodiments, the liquid distributor further comprises an elongated wall element adapted to be connected to the chamber wall, wherein the inlet orifices are formed in the wall element. The flow redirecting wall may be releasably attached to the wall element, for instance by means of screws. This may be advantageous since the slots can be conveniently cleaned. The liquid distributor may further comprise a throttle plate being provided with at least two, or a plurality of, throttling orifices, said throttle plate being arranged with the at least two, or plurality of, throttling orifices downstream of, and aligned with, corresponding at least two, or plurality of, inlet orifices to throttle the liquid flow therethrough. Preferably, the throttle plate is provided with throttling orifices for each inlet orifice. The throttle plate may be formed separately from the flow directing device to be user replaceable, i.e. be releasably formed from the rest of the liquid distributor. This is advantageous since the liquid flow through the inlet orifices may be adjusted by replacing the throttle plate. The throttle plate may be arranged sandwiched between the flow directing device (or more specifically the separating wall(s)) and the wall element. ln an alternative embodiment, the inlet orifices may be provided with throttling means, for instance in the form of releasably attached fixed diameter throttling orifices. This is a particularly advantageous embodiment when the inlet orifices are formed in the chamber wall. The throttling orifices may be threadedly attached to the chamber wall. ln yet an alternative embodiment, the inlet orifices may have effective flow areas adapted for a predetermined flow over each orifice, i.e. the inlet orifices act as throttling orifices themselves. ln particular, the inlet orifices may have different effective flow areas chosen along the longitudinal direction of the liquid distributor such as to reduce a variation in flow between the different inlet orifices.

According to a second aspect of the invention, there is provided an apparatus for washing of cellulose pulp, which apparatus comprises at least one rotatable press roll having a permeable outer surface, and at least one corresponding chamber wall at least partly enclosing the roll to define a pulp treatment chamber between said roll and said wall, at least one pulp distribution device extending along the length of the press roll, said pulp distribution device comprising an inlet and an outlet, and being arranged to distribute pulp through its outlet onto said permeable outer surface, and at least one liquid distributor according to the first aspect of the invention or embodiments thereof.

The features of the embodiments described above are combinable in any practically realizable way to form embodiments having combinations of these features.

BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the present invention will now be described in more detail with reference to the appended drawings, which show presently preferred embodiments of the invention, wherein: fig. 1 illustrates a prior art apparatus for washing of cellulose pulp; fig. 2a-b illustrate an embodiment of a liquid distributor according to the first aspect of the invention along with a portion of a press roll and chamber wall of an apparatus for washing cellulose pulp; fig. 3a-b illustrate another embodiment of a liquid distributor according to the first aspect of the invention along with a portion of a press roll and chamber wall of an apparatus for washing cellulose pulp, and fig. 4a-b illustrate yet another embodiment of a liquid distributor according to the first aspect of the invention along with a portion of a press roll and chamber wall of an apparatus for washing cellulose pulp.

DETAILED DESCRIPTION Fig. 1 illustrates a prior art apparatus for washing of cellulose pulp in the form of a twin roll press comprising two co-acting cylindrical press rolls 2. The press rolls 2 are arranged to rotate in opposite directions R, R' during operation and each has a permeable outer surface 4. The apparatus further comprises a vat having chamber walls 5 which partly encloses the rolls 2 to define a pulp treatment chamber 8 between the rolls and the corresponding chamber wall. Pulp is distributed onto the permeable outer surface 4 by means of pulp distribution devices 1. A pulp web is formed on the permeable outer surfaces 4 of the rolls. The pulp web is transported in the pulp treatment chamber 8, in the direction of rotation Fi, R' to be pressed at the nip 3 where the distance between the press rolls 2 is smallest. The press rolls 2 comprise axial filtrate channels 6, which receive filtrate from the pulp web. The filtrate passes through the permeable roll surface 4 and is transported towards the ends of the press rolls 2, where it is output. Washing liquid is supplied to the pulp web in the vat chamber 8 through liquid distributors 10. The pulp is output by means of a discharge screw Figures 2a-b illustrate an embodiment of a liquid distributor 1 10 according to the first aspect of the invention, along with a portion of a press roll and chamber wall of an apparatus of the same type as in fig. 1. The liquid distributor 1 12 thus replaces the one or both liquid distributors 10 in fig. 1. Fig. 2a shows a cross-section view of (part of) the press roll 102 and the chamber wall 105, where the pulp treatment chamber 108 is defined therebetween. Fig. 2b shows a view radially outwards of the chamber wall 105 as seen in the radial direction from within of the press roll. The liquid distributor 110 comprises a plurality of inlet orifices 111a-b distributed along a longitudinal direction L of the liquid distributor. ln this embodiment, the inlet orifices are formed as through holes in the chamber wall 105. Each inlet orifice is provided with flow directing means 112 forming a slot 113a-b for each inlet orifice. Each slot has a tangential opening 114 facing in a substantially tangential direction of the press roll. The opening is disposed adjacent the chamber wall 105 to direct said flow along the chamber wall.

All slots are formed immediately adjacent each other to form a common slot, such as to form a lateral opening 121 along the whole tangential length 117a of the slots. Thus, the flow directing means 112 of each pair of adjacent inlet orifices are provided with a lateral opening 121 between their slots. ln the figure, imaginary dash-dotted lines are shown between the inlet orifices as to indicate the respective slot portion for each inlet orifice. The lateral openings have an overall effective flow area which is less than twice the effective flow area of each tangential opening. ln this embodiment, the slot has a constant height as seen in the radial direction, which means that the tangential length 117a is longer than the longitudinal length/width 117b of each slot, but shorter than twice the longitudinal length. The common slot is formed by a flow directing device comprising a substantially tangentially extending flow redirecting wall 116 being arranged at a distance from the chamber wall 105 by means of a spacing strip 116' which may be integrally formed with the flow redirecting wall or be part of the flow directing device. The flow redirecting wall 116 is releasably attached to the chamber wall 105 for instance by means of screws (122a-b for instance) through spacing strip 116' are shown in fig. 2b. ln embodiments, the whole flow directing device comprising the wall 116 and spacing strip 116' is releasably attached to the chamber wall Figures 3a-b illustrate another embodiment of a liquid distributor 210 according to the first aspect of the invention, along with a portion of a press roll and chamber wall of an apparatus of the same type as in fig. 1. The liquid distributor 210 thus replaces the one or both liquid distributors 10 in fig. 1. Fig. 3a shows a cross-section view of (part of) the press roll 202 and the chamber wall 205, where the pulp treatment chamber 208 is defined therebetween. Fig. 3b shows a view radially outwards of the chamber wall 205 as seen in the radial direction from within of the press roll. The liquid distributor 210 comprises a plurality of inlet orifices 21 fa-b distributed along a Iongitudinal direction L of the liquid distributor. ln this embodiment, the inlet orifices are formed as through holes in the chamber wall 205. Each inlet orifice is provided with flow directing means 212 forming a slot 213a-b for each inlet orifice. Each slot has a tangential opening 214 facing in a substantially tangential direction of the press roll. The opening is disposed adjacent the chamber wall 205 to direct said flow along the chamber wall. The flow redirecting wall 216 is releasably attached to the chamber wall 205 for instance by means of screws (shown in fig. 3b in a corresponding manner as in fig. 2b).

Each inlet orifice is provided with releasably attached fixed diameter throttling orifices 220 (also shown as dotted lines below the chamber wall 205 in fig. 3b). The throttling orifices 220 may be threadedly attached to the chamber wall 205. The throttling orifices are provided with through holes of a smaller diameter than the inlet orifices, thus throttling the flow.

The flow directing means 212 of each adjacent pair of inlet orifices form longitudinally adjacent slots being separated by means of separating walls (215 for instance) which extend along the whole tangential length of the slots. Thus, unlike the embodiment in fig. 2a-b, there are no lateral openings between the slots. As can be seen in fig. 3b, the separating walls (215 for example) are formed such that each slot has an expanding cross-section along its extension in a liquid flow direction, i.e. to the left in the figures. All flow directing means 212 are formed by a flow directing device comprising a substantially tangentially extending flow redirecting wall 216 and the separating walls. The separating walls are integrally formed as one unit which also acts as a spacing means for arranging the flow redirecting wall 216 at a distance from chamber wall 205. Thus, the separating wall unit is sandwiched between the flow redirecting wall 216 and chamber wall Figures 4a-b illustrate yet another embodiment of a liquid distributor 310 according to the first aspect of the invention, along with a portion of a press roll and chamber wall of an apparatus of the same type as in fig. 1. The liquid distributor 310 thus replaces the one or both liquid distributors 10 in fig. 1. Fig. 4a shows a cross-section view of (part of) the press roll 302 and the chamber wall 305, where the pulp treatment chamber 308 is defined therebetween. Fig. 4b shows a view radially outwards of the chamber wall 305 as seen in the radial direction from within of the press roll. The liquid distributor 310 comprises a plurality of inlet orifices 311a-b distributed along a longitudinal direction L of the liquid distributor. The liquid distributor 310 comprises an elongated wall element 318 attached to the chamber wall 305. ln other embodiments, the wall element 318 is releasably attached to the chamber wall 305, for instance by means of screws. The inlet orifices 311a-b are formed in the wall element. The wall element is arranged in a longitudinal slot in the chamber wall 305, and an inner surface 318” along with the flow redirecting wall 316 form part of the overall chamber wall which partly encloses the roll The flow directing means 312 of each adjacent pair of inlet orifices form longitudinally adjacent slots being separated by means of separating walls 315 which extend along the whole tangential length of the slots in a similar manner as in fig. 3a-b. As can be seen in fig. 4b, the separating walls (315 for example) are formed such that each slot has an expanding cross-section along of its extension in a liquid flow direction, i.e. to the left in the figures. All flow directing means 312 are formed by a flow directing device comprising a substantially tangentially extending flow redirecting wall 316 and the separating walls 315. ln this embodiment, just like in fig. 3a-b, all separating walls are integrally formed as one unit which also acts as spacing means for arranging the wall 316 at a distance from wall element The liquid distributor further comprises a throttle plate 319 being provided with a plurality of throttling orifices (319a-b for instance). The throttle plate is arranged with its throttling orifices downstream of, and aligned with, corresponding inlet orifices to throttle the liquid flow therethrough.

The flow directing device 315, 316 is releasably attached to the wall element 318 for instance by means of screws shown in fig. 4b in a corresponding manner as in fig. 2b. The throttle plate 319 is formed separately from the flow directing device 315, 316 to be user replaceable. The throttle plate 319 is arranged sandwiched between the flow directing device and the wall element Each inlet orifice is provided with flow directing means 312 forming a slot 313a-b for each inlet orifice. Each slot has a tangential opening 314 facing in a substantially tangential direction of the press roll. The openings 314 are disposed adjacent the wall element surface 318' to direct the flow along the chamber wall.

The description above and the appended drawings are to be considered as non- limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example, the number of inlet orifices and the spacing therebetween may be varied. Further, the separating walls as shown in fig. 3a-b and 4a-b do not necessarily need to extend along the full length of the slots.

Claims (1)

1. An apparatus for washing cellulose pulp, which apparatus comprises - at least one rotatable press roll (102; 202; 302) having a permeable outer surface (104; 204; 304), and at least one corresponding chamber wall (1 05; 205; 305) at least partly enclosing the roll to define a pulp treatment chamber (108; 208; 308) between said roll and said wall, - at least one pulp distribution device extending along the length of the press roll, said pulp distribution device comprising an inlet and an outlet, and being arranged to distribute pulp through its outlet onto said permeable outer surface, and - at least one liquid distributor being adapted to distribute liquid into said pulp treatment chamber, said liquid distributor comprises: - a plurality of inlet orifices (111a-b; 211a-b; 311a-b) distributed along a longitudinal direction (L) of the liquid distributor, the longitudinal direction being substantially parallel with the axis of rotation of the press roll, wherein said inlet orifices (11 1a-b; 211a-b) are formed wherein said liquid distributor comprises an elongated wall element (318) said chamber wall , or adapted to be connected to the chamber wall (305), the inlet orifices (311a-b) being formed in the wall element; - each inlet orifice being provided with flow directing means (112; 212; 312)_\ formggš a slot 3a-b; 313a- ;---214; 314) facing in a tangential direction of the press roll, said opening being b) for each inlet orifice, said slot having a tangential opening arranged adjacent said chamber wall (105; 205; 305) to direct said flow along said chamber wall, “ frflsaid flow directing means (212; 312) of at least two adjacent inlet __form§_:_*_:_~¿;¿ longitudinally adjacent slots being separated by means of a separating wall (215; 315) which extends along the whole tangential length of said longitudinally adjacent slots, gämprovided with one or more lateral openings (121) between their slots, said one or more lateral openings having an overall effective flow area which is less than twice the effective flow area of each S I O a n S O.. 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(Apparatus according to claim 3 or wherein when the liquid distributor comprises an elongated wall element (318) adapted to be connected to the chamber wall (305) with the inlet orifices (311a-b) being formed in the wall element, the flow redirecting wall (316) is releasably attached to the wall element. Apparatus according to any of the preceding claims, wherein when the liquid distributor comprises an elongated wall element (318) adapted to be connected to the chamber wall (305) with the inletorifices (31 1a-b) being formed in the wall element, the liquid distributor further comprises a throttle plate (319) being provided with at least two throttling orifices (319a-b), said throttle plate being arranged with the at least two throttling orifices downstream of corresponding at least two inlet orifices to throttle the liquid flow therethrough. Apparatus according to claim wherein the throttle plate (319) is formed separately from the flow directing device to be user replaceable. Apparatus according to claim wherein the throttle plate (319) is arranged sandwiched between the flow directing device and the wall element (318). Apparatus according to any of claims wherein at least two of said throttling orifices (319a-b) have different diameters. Apparatus according to claim 3 or wherein the flow redirecting wall (116; 216) is releasably attached to the chamber wall (105; 205).