WO2019245422A1 - Vacuum filter - Google Patents

Vacuum filter Download PDF

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Publication number
WO2019245422A1
WO2019245422A1 PCT/SE2019/050468 SE2019050468W WO2019245422A1 WO 2019245422 A1 WO2019245422 A1 WO 2019245422A1 SE 2019050468 W SE2019050468 W SE 2019050468W WO 2019245422 A1 WO2019245422 A1 WO 2019245422A1
Authority
WO
WIPO (PCT)
Prior art keywords
hollow shaft
rotating
rotating hollow
arrangement
pulp
Prior art date
Application number
PCT/SE2019/050468
Other languages
French (fr)
Inventor
Åke SUNDSTRÖM
Jonas Magnusson
Anders LÖFSTRAND
Peter Nykvist
Jörgen Lundberg
Original Assignee
Valmet Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Valmet Ab filed Critical Valmet Ab
Priority to EP19821796.0A priority Critical patent/EP3810300B1/en
Priority to CA3099289A priority patent/CA3099289A1/en
Priority to US17/252,429 priority patent/US11980837B2/en
Publication of WO2019245422A1 publication Critical patent/WO2019245422A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D33/00—Filters with filtering elements which move during the filtering operation
    • B01D33/06—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums
    • B01D33/067—Construction of the filtering drums, e.g. mounting or sealing arrangements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D33/00—Filters with filtering elements which move during the filtering operation
    • B01D33/06—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums
    • B01D33/073—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums arranged for inward flow filtration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D33/00—Filters with filtering elements which move during the filtering operation
    • B01D33/06—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums
    • B01D33/073—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums arranged for inward flow filtration
    • B01D33/09—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums arranged for inward flow filtration with surface cells independently connected to pressure distributors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D33/00—Filters with filtering elements which move during the filtering operation
    • B01D33/44—Regenerating the filter material in the filter
    • B01D33/46—Regenerating the filter material in the filter by scrapers, brushes nozzles or the like acting on the cake-side of the filtering element
    • B01D33/466—Regenerating the filter material in the filter by scrapers, brushes nozzles or the like acting on the cake-side of the filtering element scrapers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D33/00—Filters with filtering elements which move during the filtering operation
    • B01D33/58—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D33/00—Filters with filtering elements which move during the filtering operation
    • B01D33/58—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element
    • B01D33/62—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element for drying
    • B01D33/64—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element for drying by compression
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D33/00—Filters with filtering elements which move during the filtering operation
    • B01D33/70—Filters with filtering elements which move during the filtering operation having feed or discharge devices
    • B01D33/74—Filters with filtering elements which move during the filtering operation having feed or discharge devices for discharging filtrate
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D33/00—Filters with filtering elements which move during the filtering operation
    • B01D33/80—Accessories
    • B01D33/82—Means for pressure distribution
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
    • D21C9/06—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents in filters ; Washing of concentrated pulp, e.g. pulp mats, on filtering surfaces
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D33/00—Filters with filtering elements which move during the filtering operation
    • B01D33/06—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums

Definitions

  • the present invention relates in general to washing and filtering equipment and in particular to arrangements in connection with pulp filters.
  • fibers are typically treated in different steps with different liquors. Within the process, different used liquors or unwanted products have to be removed from the pulp at different stages. It is thus common to use different kinds of washing equipment, typically in connection with different kinds of filters.
  • a drum vacuum filter Such a filter comprises a rotatable drum mounted in a vat provided with pulp suspension.
  • the outer surface of the drum is perforated and allows penetration of liquids.
  • A“vacuum”, or at least an underpressure, is applied on the inside of the outer surface of the drum, causing a suction of liquid through the outer surface. This causes pulp to settle onto the outer surface.
  • the pulp cake will follow the drum up from the vat and the water content in the pulp cake is reduced by further suction of liquids through the outer surface.
  • Different washing steps can also be provide here.
  • the pulp cake When the pulp cake is as dry as requested, it is removed from the drum. In order to facilitate this removal, the vacuum is no longer applied during that stage.
  • This is arranged for by a cylindrical valve.
  • a cylindrical valve In other words, in a vacuum filter with a cylindrical valve, there are in general two zones. One zone where the“vacuum” is applied over the pulp web and drain the pulp web and one zone without vacuum for enabling the release of the pulp web. The zones are defined by the cylindrical valve.
  • a problem with this setup is that the cylindrical valve is designed so that the transition from non-vacuum to“full vacuum” occurs fast, which leads to that fibers may densely fill up the closest layer on the drum surface. This is particularly common for short fiber pulp. The pulp web then becomes dense, which deteriorate the dewatering and the release of the pulp web, which in turn deteriorate the washing.
  • a general object is to improve the density distribution in the pulp web in a pulp-filter arrangement.
  • a pulp-filter arrangement comprises a rotatable drum enclosed by a non-rotating casing and a non-rotating valve arrangement.
  • the rotatable drum has a cylindrical water-permeable pulp supporting shell, a plurality of drain pipes and a rotating hollow shaft.
  • the plurality of drain pipes connects the rotating hollow shaft with a collecting channel.
  • the collecting channel is situated radially directly inside the cylindrical water-permeable pulp-supporting shell, thereby enabling a drain of liquid, passing radially inwards through the cylindrical water-permeable pulp-supporting shell, through the rotating hollow shaft.
  • the non-rotating valve arrangement is disposed within the rotating hollow shaft.
  • the non rotating valve arrangement is arranged for sealing off the hollow part of the rotating hollow shaft from a radially inner outlet of the plurality of drain pipes when respective radially inner outlet during rotation of the rotatable drum in a rotation direction is situated within a sealed zone.
  • the non-rotating valve arrangement is further arranged to, in a transition zone immediately following the sealed zone in the rotation direction, open a throttled passage between the rotating hollow shaft and the radially inner outlet of the plurality of drain pipes.
  • the throttled passage is narrower than a fully open passage between said rotating hollow shaft ( 18) and said radially inner outlet (24).
  • FIG. 1 schematically illustrates an embodiment of a vacuum filter in an elevational view
  • FIG. 2 schematically illustrate a cross-sectional view of an embodiment of a vacuum filter
  • FIG. 3 schematically illustrate an embodiment of a non-rotating valve arrangement in a vacuum filter
  • FIG. 4 schematically illustrates a top view of an embodiment of a valve plate of a non-rotating valve arrangement in a vacuum filter
  • FIG. 5 schematically illustrates a top view of another embodiment of a valve plate of a non-rotating valve arrangement in a vacuum filter
  • FIG. 6 schematically illustrates a top view of yet another embodiment of a valve plate of a non-rotating valve arrangement in a vacuum filter
  • FIG. 7 schematically illustrates a top view of yet another embodiment of a valve plate of a non-rotating valve arrangement in a vacuum filter.
  • FIG. 8 schematically illustrates a top view of yet another embodiment of a valve plate of a non-rotating valve arrangement in a vacuum filter.
  • FIG. 1 shows an embodiment of a vacuum filter in an elevational view. Some parts are broken away to allow illustration of the inner parts of the pulp-filter arrangement 1.
  • the pulp-filter arrangement 1 comprises a rotatable drum 10 enclosed by a non-rotating casing 12.
  • the rotatable drum 10 has a pulp supporting shell 14, a plurality of drain pipes 16 and a rotating hollow shaft 18.
  • the pulp-supporting shell 14 is cylindrical and water-permeable.
  • the pulp-supporting shell 14 comprises a mantle decking 13 and a filter wire 15.
  • the drain pipes 18 connect the rotating hollow shaft 18 with a collecting channel 22.
  • the collecting channels 22 are situated radially directly inside the pulp-supporting shell 14. The collecting channels 22 thereby enable a drain of liquid, passing radially inwards through the pulp-supporting shell 14. The liquid is drained through the rotating hollow shaft 18.
  • An underpressure-providing arrangement 38 constituted by a drop leg 36, is arranged to provide an underpressure within a hollow part 37 of the rotating hollow shaft 18.
  • the drop leg 36 is thus connected to the rotating hollow shaft 18.
  • the underpressure-providing arrangement 38 may comprise any type of pump.
  • pulp suspension is provided in a vat 32, surrounding the lower part of the rotatable drum 10.
  • the underpressure of the hollow part 37 of the rotating hollow shaft 18 is provided to the collecting channel 22 via the drain pipes 16, resulting in that liquids from the pulp suspension is drawn through the pulp-supporting shell 14. This causes pulp to settle against the pulp-supporting shell 14, starting to build up a pulp web 20.
  • the pulp supporting shell 14 is covered by a pulp web 20.
  • the pulp web 20 When the pulp web 20 is drained from unnecessary liquids, the pulp web 20 is removed from the pulp-supporting shell 14 by a take-off device 28 comprising e.g. a doctor table 26. The removed and possibly cut pulp web is transported out from the pulp-filter arrangement 1 by a screw conveyor 34. The removal of the pulp web is facilitated by providing a vacuum free zone or a sealed zone at the sectors where the removal is performed.
  • a take-off device 28 comprising e.g. a doctor table 26.
  • the removed and possibly cut pulp web is transported out from the pulp-filter arrangement 1 by a screw conveyor 34.
  • the removal of the pulp web is facilitated by providing a vacuum free zone or a sealed zone at the sectors where the removal is performed.
  • the pulp-filter arrangement 1 further comprises a non-rotating valve arrangement 30 disposed within the rotating hollow shaft 18.
  • the non rotating valve arrangement 30 comprises a valve shaft 31 parallel to the rotating hollow shaft 18.
  • the non-rotating valve arrangement 30 is arranged for sealing off the hollow part 37 of the rotating hollow shaft 18 from a radially inner outlet 24 of the drain pipes 16. This sealing off is provided when respective radially inner outlet 24, during rotation of the rotatable drum 10 in the rotation direction R, is situated within a sealed zone.
  • the sealed zone will be discussed more in detailed below.
  • the non-rotating valve arrangement 30 comprises a sealing plate 40 positioned against an inner surface 17 of the rotating hollow shaft 18 at the radially inner outlets 24 of the drain pipes 16 in the sealed zone.
  • the sealing plate 40 has a shape of a part of a cylinder with an outer radius equal to an inner radius of the rotating hollow shaft 18.
  • the valve shaft 31 supports the sealing plate 40.
  • the non-rotating valve arrangement 30 By configuring the non-rotating valve arrangement 30 in such a way that the vacuum is not fully applied at once when the drain pipes 16 leaves the sealed zone, the fibers from the pulp suspension will be placed on the pulp supporting shell 14 of the rotating drum 10 in a less dense manner. When the “full vacuum” is applied, a pressure drop over the existing pulp web 20 will counteract the formation of a dense pulp web 20 in the continued process.
  • the careful opening in the non-rotating valve arrangement 30 can be realized e.g. by slits, holes or oblique cutting, as will be further discussed below.
  • the non-rotating valve arrangement 30 is further arranged to open a throttled passage between the rotating hollow shaft 18 and the radially inner outlet 24 of said drain pipes 16.
  • the throttled passage is narrower than a fully open passage between the rotating hollow shaft 18 and the radially inner outlet 24. This careful opening takes place in a transition zone immediately following the sealed zone in the rotation direction R.
  • the non-rotating valve arrangement 30 is arranged to gradually open the throttled passage when the rotatable drum 10 rotates in the rotation direction R.
  • the non-rotating valve arrangement 30 comprises a valve plate 42 positioned against the inner surface of the rotating hollow shaft 18 at the radially inner outlet 24 of the drain pipes 16 in the transition zone.
  • the valve plate 42 has a shape of a part of a cylinder with an outer radius equal to an inner radius of the rotating hollow shaft 18.
  • the valve plate 42 presents at least one opening with an opening area that is smaller than a fully open passage.
  • the least one opening 60 has an opening area that averaged over a width of the radially inner outlet 24 of the drain pipes 16 gradually increases in the rotation direction R.
  • the valve shaft 31 also supports the valve plate 42.
  • Figure 2 illustrates an embodiment of a vacuum filter in a cross-sectional view.
  • a pulp source 35 provides pulp suspension 33 into the vat 32.
  • pulp will settle on the pulp-supporting shell, forming the pulp web 20. This action is supported by the vacuum provided by the rotating hollow shaft 18 and the drain pipes 16.
  • the vacuum is applied in an open zone 52.
  • the pulp web 20 does not grow in thickness any more, but instead the vacuum can be utilized to remove parts of the liquids of the pulp.
  • different washing steps can be applied within the open zone 52. These washing steps are preferably performed according to well-known prior art and are not influencing the main topics of the presently presented ideas. Therefore, such additional operations and arrangements are not further discussed in order to simplify the description.
  • the non-rotating valve arrangement 30 is arranged for sealing off the hollow part 37 of the rotating hollow shaft 18 from the radially inner outlet of the drain pipes 16. This sealing off is provided when respective radially inner outlet, during rotation of the rotatable drum 10 in the rotation direction R, is situated within the sealed zone 50. In this embodiment, the sealing off is performed by the sealing plate 40, sealing against the inner surface 17 of the rotating hollow shaft 18.
  • the take-off device 28 removes the pulp web 20 and the bare pulp-supporting shell 14 can once again be brought down in the pulp suspension 33 of the vat 32.
  • transition zone 54 When the vacuum once more is applied to the inside of the pulp supporting shell 14, this is performed gradually within the transition zone 54, in order to avoid a too dense pulp web closest to the pulp-supporting shell 14.
  • a passage is gradually opened between the rotating hollow shaft 18 and the radially inner outlet of the drain pipes 16 when the rotatable drum 10 rotates in the rotation direction R.
  • the transition zone 54 is situated immediately after the sealed zone 50 in the rotation direction R.
  • the valve plate 42 is in this embodiment positioned against the inner surface 17 of the rotating hollow shaft 18.
  • FIG. 3 A close-up view of an embodiment of the non-rotating valve arrangement 30 and the parts cooperating therewith is illustrated in Figure 3.
  • valve plate 42 presents an opening 60, which gradually widens in the rotational direction R.
  • valve plate 42 presents a V-shaped opening 61.
  • a sealing material 46 is built-up in a two-layer configuration, having a radially outer layer of a sealing material 46 provided in a close vicinity of the inner surface 17 of the rotating hollow shaft 18, however, typically with a very small slit therebetween.
  • This radially outer layer of a sealing material 46 is supported by a radially inner rigid layer 44.
  • This configuration can alternatively also be provided just to one of the sealing plate 40 and the valve plate 42.
  • the transition zone 54 covers at least two, more preferably at least four, and most preferably at least six of the radially inner outlets of the plurality of drain pipes 16 at a time. In this particular embodiment, the transition zone 54 covers six of the radially inner outlets of the plurality of drain pipes 16 at a time.
  • the valve plate 42 can be configured in many different ways. Common for the preferred embodiments is that an average total area, e.g. averaged over the width of a drain pipe, of the holes through the valve plate 42 gradually increases in the rotational direction. This gradual increase may be continuous or discrete.
  • FIG. 4 a top view of an embodiment of a valve plate 42 of a non-rotating valve arrangement 30 in a vacuum filter is schematically illustrated. This design is essentially the same as shown in Figure 2, where the opening 60 is a V-shaped opening 61.
  • FIG. 5 a top view of another embodiment of a valve plate 42 of a non-rotating valve arrangement 30 in a vacuum filter is schematically illustrated.
  • This embodiment presents a series of holes 62 with increasing area.
  • valve plate 42 presents holes 62, wherein an average total area of the holes 62 increases in the rotation direction.
  • FIG. 6 a top view of yet another embodiment of a valve plate 42 of a non rotating valve arrangement 30 in a vacuum filter is schematically illustrated.
  • This embodiment presents a number of slits 63 with different lengths along the rotation direction R.
  • the valve plate 42 presents slits 63, an average total area of the slits 63 increases in the rotation direction R.
  • FIG. 7 a top view of yet another embodiment of a valve plate 42 of a non rotating valve arrangement 30 in a vacuum filter is schematically illustrated.
  • This embodiment also presents a number of holes 64, but with the same area. Instead, the number of holes increases in the direction along the rotation direction R, giving rise to a gradually increasing average total area.
  • FIG. 8 a top view of yet another embodiment of a valve plate 42 of a non rotating valve arrangement 30 in a vacuum filter is schematically illustrated.
  • This embodiment presents oblique cuts 65.
  • the valve plate 42 presents oblique cuts 65.
  • An average total area of the valve plate 42 that is removed by the oblique cuts 65 increases in the rotation direction.

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  • Chemical Kinetics & Catalysis (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
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Abstract

A pulp-filter arrangement (1) comprises a rotatable drum (10) and a non-rotating valve arrangement (30). The rotatable drum (10) has a cylindrical water-permeable pulp-supporting shell (14), a plurality of drain pipes (16) and a rotating hollow shaft (18). The plurality of drain pipes (16) connects the rotating hollow shaft (18) with a collecting channel (22)situated radially directly inside the cylindrical water-permeable pulp-supporting shell(14). The non-rotating valve arrangement (30) is disposed within the rotating hollow shaft(18)for sealing off the rotating hollow shaft (18) from a radially inner outlet (24) of the drain pipes (16) when respective radially inner outlet (24) is situated within a sealed zone. The non-rotating valve arrangement (30) is further arranged to, in a transition zone immediately following the sealed zone, open a throttled passage between the rotating hollow shaft (18) and the radially inner outlet (24).

Description

VACUUM FILTER
TECHNICAL FIELD
The present invention relates in general to washing and filtering equipment and in particular to arrangements in connection with pulp filters.
BACKGROUND
In a pulp production, fibers are typically treated in different steps with different liquors. Within the process, different used liquors or unwanted products have to be removed from the pulp at different stages. It is thus common to use different kinds of washing equipment, typically in connection with different kinds of filters.
One well-known type of pulp filter is a drum vacuum filter. Such a filter comprises a rotatable drum mounted in a vat provided with pulp suspension. The outer surface of the drum is perforated and allows penetration of liquids. A“vacuum”, or at least an underpressure, is applied on the inside of the outer surface of the drum, causing a suction of liquid through the outer surface. This causes pulp to settle onto the outer surface. When the drum is rotated, the pulp cake will follow the drum up from the vat and the water content in the pulp cake is reduced by further suction of liquids through the outer surface. Different washing steps can also be provide here.
When the pulp cake is as dry as requested, it is removed from the drum. In order to facilitate this removal, the vacuum is no longer applied during that stage. This is arranged for by a cylindrical valve. In other words, in a vacuum filter with a cylindrical valve, there are in general two zones. One zone where the“vacuum” is applied over the pulp web and drain the pulp web and one zone without vacuum for enabling the release of the pulp web. The zones are defined by the cylindrical valve. A problem with this setup is that the cylindrical valve is designed so that the transition from non-vacuum to“full vacuum” occurs fast, which leads to that fibers may densely fill up the closest layer on the drum surface. This is particularly common for short fiber pulp. The pulp web then becomes dense, which deteriorate the dewatering and the release of the pulp web, which in turn deteriorate the washing.
SUMMARY
A general object is to improve the density distribution in the pulp web in a pulp-filter arrangement.
The above object is achieved by methods and devices according to the independent claims. Preferred embodiments are defined in dependent claims.
In general words, in a first aspect, a pulp-filter arrangement comprises a rotatable drum enclosed by a non-rotating casing and a non-rotating valve arrangement. The rotatable drum has a cylindrical water-permeable pulp supporting shell, a plurality of drain pipes and a rotating hollow shaft. The plurality of drain pipes connects the rotating hollow shaft with a collecting channel. The collecting channel is situated radially directly inside the cylindrical water-permeable pulp-supporting shell, thereby enabling a drain of liquid, passing radially inwards through the cylindrical water-permeable pulp-supporting shell, through the rotating hollow shaft. The non-rotating valve arrangement is disposed within the rotating hollow shaft. The non rotating valve arrangement is arranged for sealing off the hollow part of the rotating hollow shaft from a radially inner outlet of the plurality of drain pipes when respective radially inner outlet during rotation of the rotatable drum in a rotation direction is situated within a sealed zone. The non-rotating valve arrangement is further arranged to, in a transition zone immediately following the sealed zone in the rotation direction, open a throttled passage between the rotating hollow shaft and the radially inner outlet of the plurality of drain pipes. The throttled passage is narrower than a fully open passage between said rotating hollow shaft ( 18) and said radially inner outlet (24).
One advantage with the slower application of vacuum provided in the proposed technology is that the dewatering and the release is improved. Other advantages will be appreciated when reading the detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which:
FIG. 1 schematically illustrates an embodiment of a vacuum filter in an elevational view;
FIG. 2 schematically illustrate a cross-sectional view of an embodiment of a vacuum filter;
FIG. 3 schematically illustrate an embodiment of a non-rotating valve arrangement in a vacuum filter; and
FIG. 4 schematically illustrates a top view of an embodiment of a valve plate of a non-rotating valve arrangement in a vacuum filter;
FIG. 5 schematically illustrates a top view of another embodiment of a valve plate of a non-rotating valve arrangement in a vacuum filter;
FIG. 6 schematically illustrates a top view of yet another embodiment of a valve plate of a non-rotating valve arrangement in a vacuum filter;
FIG. 7 schematically illustrates a top view of yet another embodiment of a valve plate of a non-rotating valve arrangement in a vacuum filter; and
FIG. 8 schematically illustrates a top view of yet another embodiment of a valve plate of a non-rotating valve arrangement in a vacuum filter.
DETAILED DESCRIPTION
Throughout the drawings, the same reference numbers are used for similar or corresponding elements. For a better understanding of the proposed technology, it may be useful to begin with a brief overview of a vacuum filter in general.
Figure 1 shows an embodiment of a vacuum filter in an elevational view. Some parts are broken away to allow illustration of the inner parts of the pulp-filter arrangement 1. The pulp-filter arrangement 1 comprises a rotatable drum 10 enclosed by a non-rotating casing 12. The rotatable drum 10 has a pulp supporting shell 14, a plurality of drain pipes 16 and a rotating hollow shaft 18. The pulp-supporting shell 14 is cylindrical and water-permeable. In this particular embodiment, the pulp-supporting shell 14 comprises a mantle decking 13 and a filter wire 15.
The drain pipes 18 connect the rotating hollow shaft 18 with a collecting channel 22. The collecting channels 22 are situated radially directly inside the pulp-supporting shell 14. The collecting channels 22 thereby enable a drain of liquid, passing radially inwards through the pulp-supporting shell 14. The liquid is drained through the rotating hollow shaft 18.
An underpressure-providing arrangement 38, constituted by a drop leg 36, is arranged to provide an underpressure within a hollow part 37 of the rotating hollow shaft 18. The drop leg 36 is thus connected to the rotating hollow shaft 18. Alternatively, the underpressure-providing arrangement 38 may comprise any type of pump.
As will be discussed further below, pulp suspension is provided in a vat 32, surrounding the lower part of the rotatable drum 10. The underpressure of the hollow part 37 of the rotating hollow shaft 18 is provided to the collecting channel 22 via the drain pipes 16, resulting in that liquids from the pulp suspension is drawn through the pulp-supporting shell 14. This causes pulp to settle against the pulp-supporting shell 14, starting to build up a pulp web 20. When a portion of the pulp-supporting shell 14, upon rotation of the rotatable drum 10 in a rotation direction R, leaves the vat 32, the pulp supporting shell 14 is covered by a pulp web 20.
In the upper part of the pulp-filter arrangement 1 , different washing steps can be implemented. In order to simplify the understanding of the basic process, such arrangements are omitted in Figure 1.
When the pulp web 20 is drained from unnecessary liquids, the pulp web 20 is removed from the pulp-supporting shell 14 by a take-off device 28 comprising e.g. a doctor table 26. The removed and possibly cut pulp web is transported out from the pulp-filter arrangement 1 by a screw conveyor 34. The removal of the pulp web is facilitated by providing a vacuum free zone or a sealed zone at the sectors where the removal is performed.
To this end, the pulp-filter arrangement 1 further comprises a non-rotating valve arrangement 30 disposed within the rotating hollow shaft 18. The non rotating valve arrangement 30 comprises a valve shaft 31 parallel to the rotating hollow shaft 18. The non-rotating valve arrangement 30 is arranged for sealing off the hollow part 37 of the rotating hollow shaft 18 from a radially inner outlet 24 of the drain pipes 16. This sealing off is provided when respective radially inner outlet 24, during rotation of the rotatable drum 10 in the rotation direction R, is situated within a sealed zone. The sealed zone will be discussed more in detailed below.
The non-rotating valve arrangement 30 comprises a sealing plate 40 positioned against an inner surface 17 of the rotating hollow shaft 18 at the radially inner outlets 24 of the drain pipes 16 in the sealed zone. The sealing plate 40 has a shape of a part of a cylinder with an outer radius equal to an inner radius of the rotating hollow shaft 18. In this embodiment, the valve shaft 31 supports the sealing plate 40.
By configuring the non-rotating valve arrangement 30 in such a way that the vacuum is not fully applied at once when the drain pipes 16 leaves the sealed zone, the fibers from the pulp suspension will be placed on the pulp supporting shell 14 of the rotating drum 10 in a less dense manner. When the “full vacuum” is applied, a pressure drop over the existing pulp web 20 will counteract the formation of a dense pulp web 20 in the continued process. The careful opening in the non-rotating valve arrangement 30 can be realized e.g. by slits, holes or oblique cutting, as will be further discussed below.
In order to provide the careful opening the non-rotating valve arrangement 30 is further arranged to open a throttled passage between the rotating hollow shaft 18 and the radially inner outlet 24 of said drain pipes 16. The throttled passage is narrower than a fully open passage between the rotating hollow shaft 18 and the radially inner outlet 24. This careful opening takes place in a transition zone immediately following the sealed zone in the rotation direction R.
Preferably, the non-rotating valve arrangement 30 is arranged to gradually open the throttled passage when the rotatable drum 10 rotates in the rotation direction R.
In this embodiment, the non-rotating valve arrangement 30 comprises a valve plate 42 positioned against the inner surface of the rotating hollow shaft 18 at the radially inner outlet 24 of the drain pipes 16 in the transition zone. The valve plate 42 has a shape of a part of a cylinder with an outer radius equal to an inner radius of the rotating hollow shaft 18. The valve plate 42 presents at least one opening with an opening area that is smaller than a fully open passage.
Preferably, the least one opening 60 has an opening area that averaged over a width of the radially inner outlet 24 of the drain pipes 16 gradually increases in the rotation direction R. In this embodiment, the valve shaft 31 also supports the valve plate 42. Figure 2 illustrates an embodiment of a vacuum filter in a cross-sectional view. A pulp source 35 provides pulp suspension 33 into the vat 32. Upon rotation of the rotatable drum 10 in the rotation direction R, pulp will settle on the pulp-supporting shell, forming the pulp web 20. This action is supported by the vacuum provided by the rotating hollow shaft 18 and the drain pipes 16. The vacuum is applied in an open zone 52. When the pulp web leaves the pulp suspension 33 in the vat, the pulp web 20 does not grow in thickness any more, but instead the vacuum can be utilized to remove parts of the liquids of the pulp. Furthermore, different washing steps (not illustrated) can be applied within the open zone 52. These washing steps are preferably performed according to well-known prior art and are not influencing the main topics of the presently presented ideas. Therefore, such additional operations and arrangements are not further discussed in order to simplify the description.
When a portion of the pulp web 20 is ready to be removed, a corresponding part of the rotatable drum 10 enters into the sealed zone 50. In this sealed zone 50, the non-rotating valve arrangement 30 is arranged for sealing off the hollow part 37 of the rotating hollow shaft 18 from the radially inner outlet of the drain pipes 16. This sealing off is provided when respective radially inner outlet, during rotation of the rotatable drum 10 in the rotation direction R, is situated within the sealed zone 50. In this embodiment, the sealing off is performed by the sealing plate 40, sealing against the inner surface 17 of the rotating hollow shaft 18. The take-off device 28 removes the pulp web 20 and the bare pulp-supporting shell 14 can once again be brought down in the pulp suspension 33 of the vat 32.
When the vacuum once more is applied to the inside of the pulp supporting shell 14, this is performed gradually within the transition zone 54, in order to avoid a too dense pulp web closest to the pulp-supporting shell 14. In the transition zone 54, a passage is gradually opened between the rotating hollow shaft 18 and the radially inner outlet of the drain pipes 16 when the rotatable drum 10 rotates in the rotation direction R. The transition zone 54 is situated immediately after the sealed zone 50 in the rotation direction R. The valve plate 42 is in this embodiment positioned against the inner surface 17 of the rotating hollow shaft 18.
A close-up view of an embodiment of the non-rotating valve arrangement 30 and the parts cooperating therewith is illustrated in Figure 3. A valve support
41 mechanically connects the valve shaft 31 of the non-rotating valve arrangement 30 with the sealing plate 40 and the valve plate 42. In this embodiment, the valve plate 42 presents an opening 60, which gradually widens in the rotational direction R. In this particular embodiment, the valve plate 42 presents a V-shaped opening 61.
Also, in the embodiment of Figure 3, the sealing plate 40 and the valve plate
42 are built-up in a two-layer configuration, having a radially outer layer of a sealing material 46 provided in a close vicinity of the inner surface 17 of the rotating hollow shaft 18, however, typically with a very small slit therebetween. This radially outer layer of a sealing material 46 is supported by a radially inner rigid layer 44. This configuration can alternatively also be provided just to one of the sealing plate 40 and the valve plate 42.
It is preferably if the transition zone 54 covers at least two, more preferably at least four, and most preferably at least six of the radially inner outlets of the plurality of drain pipes 16 at a time. In this particular embodiment, the transition zone 54 covers six of the radially inner outlets of the plurality of drain pipes 16 at a time.
The valve plate 42 can be configured in many different ways. Common for the preferred embodiments is that an average total area, e.g. averaged over the width of a drain pipe, of the holes through the valve plate 42 gradually increases in the rotational direction. This gradual increase may be continuous or discrete.
In Fig. 4, a top view of an embodiment of a valve plate 42 of a non-rotating valve arrangement 30 in a vacuum filter is schematically illustrated. This design is essentially the same as shown in Figure 2, where the opening 60 is a V-shaped opening 61.
In Fig. 5, a top view of another embodiment of a valve plate 42 of a non-rotating valve arrangement 30 in a vacuum filter is schematically illustrated. This embodiment presents a series of holes 62 with increasing area. In other words, valve plate 42 presents holes 62, wherein an average total area of the holes 62 increases in the rotation direction.
In Fig. 6, a top view of yet another embodiment of a valve plate 42 of a non rotating valve arrangement 30 in a vacuum filter is schematically illustrated. This embodiment presents a number of slits 63 with different lengths along the rotation direction R. In other words, the valve plate 42 presents slits 63, an average total area of the slits 63 increases in the rotation direction R.
In Fig. 7, a top view of yet another embodiment of a valve plate 42 of a non rotating valve arrangement 30 in a vacuum filter is schematically illustrated. This embodiment also presents a number of holes 64, but with the same area. Instead, the number of holes increases in the direction along the rotation direction R, giving rise to a gradually increasing average total area.
In Fig. 8, a top view of yet another embodiment of a valve plate 42 of a non rotating valve arrangement 30 in a vacuum filter is schematically illustrated. This embodiment presents oblique cuts 65. In other words, the valve plate 42 presents oblique cuts 65. An average total area of the valve plate 42 that is removed by the oblique cuts 65 increases in the rotation direction.
The embodiments described above are to be understood as a few illustrative examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible. The scope of the present invention is, however, defined by the appended claims.

Claims

1. A pulp-filter arrangement ( 1), comprising:
a rotatable drum ( 10) enclosed by a non-rotating casing ( 12);
said rotatable drum ( 10) having a cylindrical water-permeable pulp supporting shell ( 14), a plurality of drain pipes ( 16) and a rotating hollow shaft ( 18) ;
said plurality of drain pipes ( 16) connecting said rotating hollow shaft ( 18) with a collecting channel (22) situated radially directly inside said cylindrical water-permeable pulp-supporting shell ( 14), thereby enabling a drain of liquid, passing radially inwards through said cylindrical water- permeable pulp-supporting shell (14), through said rotating hollow shaft ( 18); a non-rotating valve arrangement (30) disposed within said rotating hollow shaft ( 18), arranged for sealing off the hollow part (37) of said rotating hollow shaft ( 18) from a radially inner outlet (24) of said plurality of drain pipes ( 16) when respective said radially inner outlet (24) during rotation of said rotatable drum ( 10) in a rotation direction (R) is situated within a sealed zone (50); and
an underpressure-providing arrangement (38) arranged to provide an underpressure within said rotating hollow shaft ( 18);
characterized in that said non-rotating valve arrangement (30) being further arranged to, in a transition zone (54) immediately following said sealed zone (50) in said rotation direction (R), open a throttled passage between said rotating hollow shaft ( 18) and said radially inner outlet (24) of said plurality of drain pipes ( 16), said throttled passage being narrower than a fully open passage between said rotating hollow shaft ( 18) and said radially inner outlet (24).
2. The arrangement according to claim 1, characterized in that said non-rotating valve arrangement (30) is arranged to gradually open said throttled passage when said rotatable drum ( 10) rotates in said rotation direction (R).
3. The arrangement according to claim 1 or 2, characterized in that said non-rotating valve arrangement (30) comprises a sealing plate (40) positioned against an inner surface ( 17) of said rotating hollow shaft ( 18) at the radially inner outlet (24) of said plurality of drain pipes ( 16) in said sealed zone (50), said sealing plate (40) having a shape of a part of a cylinder with an outer radius equal to an inner radius of said rotating hollow shaft ( 18); and said non-rotating valve arrangement (30) further comprises a valve plate (42) positioned against an inner surface ( 17) of said rotating hollow shaft ( 18) at the radially inner outlet (24) of said plurality of drain pipes (16) in said transition zone (54), said valve plate (42) having a shape of a part of a cylinder with an outer radius equal to an inner radius of said rotating hollow shaft ( 18), said valve plate (42) presenting at least one opening (60) with an opening area that is smaller than said fully open passage.
4. The arrangement according to claim 3, characterized in that said at least one opening (60) has an opening area that averaged over a width of said radially inner outlet (24) of said plurality of drain pipes ( 16) gradually increases in said rotation direction (R).
5. The arrangement according to claim 3 or 4, characterized in that said valve plate (42) presents a V-shaped opening (61).
6. The arrangement according to claim 3 or 4, characterized in that said valve plate (42) presents holes (62, 64), wherein an average total area of said holes (62, 64) increases in said rotation direction (R).
7. The arrangement according to claim 3 or 4, characterized in that said valve plate (42) presents slits (63), an average total area of said slits (63) increases in said rotation direction (R).
8. The arrangement according to claim 3 or 4, characterized in that said valve plate (42) presents oblique cuts (65), an average total area of the valve plate removed by said oblique cuts (65) increases in said rotation direction (R).
9. The arrangement according to any of the claims 3 to 8, characterized in that said transition zone (54) covers at least two, preferably at least four, and most preferably at least six of said radially inner outlets (24) of said plurality of drain pipes ( 16) at a time.
10. The arrangement according to any of the claims 3 to 8, characterized in that said non-rotating valve arrangement (30) comprises a valve shaft (31) parallel to said rotating hollow shaft (18), said valve shaft (31) supporting said sealing plate (40) and said valve plate (42).
1 1. The arrangement according to any of the claims 1- 10, characterized in that said underpressure-providing arrangement (38) comprises a drop leg (36) connected to said rotating hollow shaft ( 18).
PCT/SE2019/050468 2018-06-21 2019-05-22 Vacuum filter WO2019245422A1 (en)

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CA3099289A CA3099289A1 (en) 2018-06-21 2019-05-22 Vacuum filter
US17/252,429 US11980837B2 (en) 2018-06-21 2019-05-22 Rotary drum vacuum filter with a throttling valve

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CA3099289A1 (en) 2019-12-26
EP3810300A4 (en) 2022-03-09
SE542326C2 (en) 2020-04-14
EP3810300B1 (en) 2023-06-21
US20210252436A1 (en) 2021-08-19
US11980837B2 (en) 2024-05-14
SE1850778A1 (en) 2019-12-22
EP3810300A1 (en) 2021-04-28

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