CA2301164A1 - Apparatus for filtering suspensions - Google Patents
Apparatus for filtering suspensions Download PDFInfo
- Publication number
- CA2301164A1 CA2301164A1 CA002301164A CA2301164A CA2301164A1 CA 2301164 A1 CA2301164 A1 CA 2301164A1 CA 002301164 A CA002301164 A CA 002301164A CA 2301164 A CA2301164 A CA 2301164A CA 2301164 A1 CA2301164 A1 CA 2301164A1
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- Prior art keywords
- chamber
- peripheral
- fine fraction
- filter disc
- chambers
- Prior art date
- Legal status (The legal status 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 status listed.)
- Abandoned
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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
- B01D33/15—Filters with filtering elements which move during the filtering operation with rotary plane filtering surfaces
- B01D33/21—Filters with filtering elements which move during the filtering operation with rotary plane filtering surfaces with hollow filtering discs transversely mounted on a hollow rotary shaft
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D36/00—Filter circuits or combinations of filters with other separating devices
- B01D36/001—Filters in combination with devices for the removal of gas, air purge systems
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- 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
- D21C9/18—De-watering; Elimination of cooking or pulp-treating liquors from the pulp
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
- D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
- D21D5/02—Straining or screening the pulp
- D21D5/04—Flat screens
- D21D5/046—Rotary screens
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Mechanical Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- Wood Science & Technology (AREA)
- Filtration Of Liquid (AREA)
- Paper (AREA)
- Filtering Materials (AREA)
Abstract
An apparatus for filtering mat forming suspensions, such as fibre pulp suspensions, has rotating annular discs (6) with peripheral chambers (13) arranged to operate as droplegs on the ascending parts of the discs. To speed up the emptying of the chambers there are venting means (21, 23) effective to supply air into the chambers at the upwardly moving parts of the discs, when the chambers are at least partly above a body of the suspension to be filtered during rotation of the discs.
Description
Apparatus for filtering suspensions The present invention relates to an apparatus for filtering suspensions, such as fibre pulp suspensions.
EP-Bl-515492 discloses such an apparatus, which includes at least one annular vertical hollow filter disc having two opposed side walls of filter material and forming a central chamber.
Means is provided for rotating the annular filter disc about a horizontal axis extending centrally through the filter disc.
There are partition walls extending between the opposed side walls of the filter disc and positioned to divide the interior of the filter disc into a number of peripheral chambers disposed in series around the filter disc. Each peripheral chamber communicates with the central chamber via an outlet. The filter disc is adapted to be partly submerged in a body of a suspension to be filtered, such that the central chamber is at least partly submerged in said body of suspension, whereby a fine fraction of the suspension is forced by hydrostatic pressure through the side walls of filter material into the peripheral chambers and further into the central chamber via the outlets of the peripheral chambers. Means is provided to maintain a pool of fine fraction in the central chamber. The partition walls are arranged such that each peripheral chamber is at least partly above the pool of fine fraction at some point of the revolution of the filter disc at the upwardly moving part of the filter disc, while the outlet of the peripheral chamber opens into the pool of tine fraction.
The peripheral chambers of this known apparatus function as droplegs when they move upwardly, because at this stage of revolution the created mats of coarse particles covering the filter wall portions of the peripheral chambers are more or less liquid impervious. This has the advantage that the coarse fraction of the suspension is dewatered efficiently. This type of filter disc with integrated droplegs also eliminates the need for space demanding external droplegs.
However, a drawback to the apparatus of EP-B1-515492 is that the rotational speed of the disc is limited, because of the fact that each upwardly moving peripheral chamber has to be emptied before it reaches a knock-off zone, in which the mat is sprayed off the filter walls of the peripheral chamber. In the case of filtering a fibre pulp suspension of the kind which forms very tight fibre mats, so that air can only pass very slowly through the mat into the peripheral chambers, the rotational speed of the disc has to be particularly low which reduces the capacity.
The object of the present invention is to improve the filtering capacity of the type of apparatus disclosed in EP-B1-515492.
This object is- fulfilled by a filtering apparatus of the integrated dropleg type defined above, which is characterized by venting means effective to supply air into each peripheral chamber at the upwardly moving part of the filter disc, when the peripheral chamber is at least partly above the body of suspension during rotation of the filter disc, in order to speed up the emptying of the peripheral chamber.
Said supply of air into the peripheral chambers by the venting means can make the emptying of the peripheral chambers about two to three times faster, as compared with the known filtering apparatus. Therefore the rotational speed of the filter disc can be significantly increased to improve the filtering capacity of the apparatus.
The venting means is preferably adapted to supply the peripheral chambers with air from the central chamber. As an alternative, however, the venting means may comprise valves to the respective peripheral chambers adapted to open in a predetermined zone, through which the peripheral chambers pass during rotation of the filter disc, to allow air from outside the apparatus to enter the peripheral chambers.
The venting means may form venting passages extending from the central chamber into the respective peripheral chambers and preferably opening in the peripheral chambers proximate to the radially outermost and leading ends of the peripheral chambers, as seen in the direction of rotation of the filter disc. Each venting passage is inoperable as long as it does not communicate with the air above the pool of fine fraction in the central chamber. As soon as each peripheral chamber has moved upwardly to a position in which air can enter the venting passage associated to the peripheral chamber, the venting passage is operable to supply air into its peripheral chamber.
The venting passage of each peripheral chamber may open into the central chamber in advance of the outlet of the peripheral chamber, as seen in the direction of rotation of the filter disc, Which makes the function of the venting means particularly reliable.
In the most simplified embodiment of the apparatus of the invention, the venting means comprises pipes extending from the central chamber into the respective peripheral chambers to positions proximate to the leading ends of the peripheral chambers, as seen in the direction of rotation of the filter disc, whereby the interior of the pipes constitutes said venting passages.
The apparatus disclosed in EP-B1-515492 has means for separating the developed fine fraction into cloudy and clear fine fractions. Reference is also made to EP-H1-515502 disclosing said separating means in more detail. Said fine fraction separating means includes stationary rigid partition wall means extending axially in the central chamber and dividing the latter into at least two axial channels for receiving a cloudy fine fraction and a clear fine fraction, respectively. The central chamber is defined by a cylindrical wall and there is fine fraction discharge means for discharging said cloudy and clear fine fractions separately from the axial channels. The apparatus of the present invention may be designed likewise, if desired to obtain cloudy and clear fine fractions. However, it has been proven in practice that the increased rotational speed of the filter disc made possible by the above defined venting means results in an increased volume of mixed cloudy and clear fine fractions. To reduce said volume to at least some extent the partition wall means may be displaced forwards in the direction of rotation of the disc, provided that the resulted reduced flow of clear fine fraction from the apparatus is acceptable.
To allow such a fine fraction separating means to be incor-porated in the apparatus of the invention without being forced to restrict the rotational speed of the disc, so that the optimal flow of clear fine fraction can be obtained, the stationary partition wall means and the cylindrical wall define first and second distribution chambers. The first distribution chamber neighbours the axial channel for cloudy fine fraction and is adapted to receive relatively clear fine fraction flowing through the outlets of the peripheral chambers passing the first distribution chamber during rotation of the filter disc and to distribute said received relatively clear fine fraction to the axial channel f or cloudy fine fraction. The second distribution chamber neighbours the axial channel for clear fraction and is adapted to receive clear fine fraction flowing through the outlets of the peripheral chambers passing the second distri-bution chamber during rotation of the filter disc and to distribute said received clear fine fraction to the axial channel for clear fine fraction.
Since the pressures in the two distribution chambers are due to the heads between the body of suspension and the respective distribution chambers, the relatively clear fine fraction is forced from the first distribution chamber into the axial channel containing cloudy fine fraction. whereas substantially all of the clear fine fraction flowing into the second distri-bution chamber is forced into the axial channel containing clear fine fraction. Only a minor amount of clear fine fraction will pass from the second distribution chamber into the first distri-bution chamber, because of the small pressure difference between the two distribution chambers. Thus, the separation of cloudy and clear fractions can be made sharply, which enables a higher rotational speed of the filter disc, and consequently a larger flow of clear fine filtrate.
The invention is explained below in more detail by way of example with reference to the accompanying drawings, in which Figure 1 is a side view of an apparatus of the invention, Figure 2 is a sectional view along line II-II of Figure 1, Figure 3 is a part of a section along line III-III of Figure 2, Figure 4 is an enlarged view of a detail shown in Figure 1, Figure 5 is an enlarged vertical cross-section of an upwardly moving part of a filter disc for the apparatus of the invention, Figure 6 is a part of an enlarged sectional view along line VI-VI
of Figure 2, Figure 7 is a part of an enlarged sectional view along line VII-VII of Figure 2, Figure 8 is an enlarged detail of the embodiment shown in Figure 6, Figure 9 is a modification of the embodiment shown in Figure 8, and 'Figure 10 is a part of a longitudinal section along line X-X of Figure 9.
In Figures 1 and 2 there is shown an apparatus of the invention comprising a container 1 and a hollow rotor shaft 2, which forms a central chamber 3 with a cylindrical wall 4 which is journalled on the container 1, so that the shaft 2 is rotatable about a horizontal axis 5. Three annular vertical hollow filter discs 6 are mounted on the shaft 2 spaced from one another and are coaxial with the horizonta l axis 5. A drive motor 7 is connected to the shaft 2 and adapted to revolve the discs 6 in counter-clockwise direction, as shown in Fig. 1. An inlet device 8 is arranged to supply a suspension to be filtered to the container 1 at the downwardly moving side of the filter discs 6 and an outlet device 9 is located at the upwardly moving side of the filter discs 6 for receiving mats or cakes of coarse particles which are removed from the filter discs 6 by shower means 10.
Each filter disc 6 comprises two opposed side walls 11 of filter material. Partition walls 12 extend between the opposed side walls 11 and divide the interior of the filter disc into a plurality of peripheral chambers 13 (the number of chambers 13 may suitably be chosen from sixteen to twenty), the peripheral chambers 13 being disposed in series around the filter disc 6.
Each peripheral chamber 13 communicates with the central chamber 3 via an outlet 14 in the cylindrical wall 4.
In the central chamber 3 there is a means for separating developed fine fraction into cloudy and clear fine fractions.
This separation means comprises a stationary rigid partition wall means 15 dividing the central chamber 3 into an axial channel 16 for receiving cloudy fine fraction and an axial channel 3a for receiving clear fine fraction. The channel 16 extends axially along the central chamber 3 and out of the latter to an outlet device 17. Clear fine fraction is able to collect in channel 3a at the lower part of the central chamber 3 and to form a pool 18 of fine fraction therein. The level 18a of the surface of the pool 18 is determined by properly dimensioning the central chamber 3. As an alternative the level 18s may be determined by an adjustable overflow. The clear fine fraction collected in the axial channel 3a is discharged to an outlet device 19. The partition wall means 15 is turnable about said horizontal axis 5 and is connected to the container 1 by adjustment means 20 for adjusting the position of the partition wall means 15 in the central chamber 3.
Figure 5 shows the design of the peripheral chambers 13 in more detail on the upwardly moving part of the filter disc 6. Each chamber 13 is defined by two straight radially extending partition walls 12a and 12b, which at their radially innermost ends adjoin two backwardly extending slightly curved partition walls 12a' and 12b', as seen in the direcion of rotation. The radially innermost ends of the curved partition walls 12a', 12b' abut the cylindrical wall 4 at opposite sides of the outlet 14 of the peripheral chamber 13, so that the outlet 14 extends from the end of the lower curved partition wall 12b' but is spaced from the end of the upper curved partition wall 12a'.
Accordingly, there is a circumferential wall portion 4a of the cylindrical wall 4 between the outlet 14 and the end of the upper curved partition wall 12a'.
A venting means in the farm of a tube 21 extends from the central chamber 3 into each peripheral chamber 13 to a position proximate to the leading end 22 and the radially outermost part of the peripheral chamber 13. The interior of the tube 21 constitutes a passage 23 for supplying air from the central chamber 3 to the peripheral chamber 13. The tube 21 preferably extends through the wall portion 4a, but may alternatively have its lower end 21a directed to the outlet 14, suitably at the leading part of the outlet 14, as indicated in Fig. 5.
The stationary partition wall means 15 comprises three straight axially extending walls 24, 25, 25 having three longitudinal edges close to but spaced from the cylindrical wall 4 of the rotor shaft 2, at the downwardly moving part of the cylindrical wall 4, see Figs. 6 and 8. The walls 24, 25, 26 and the cylindrical wall 4 define a first distribution chamber 27 neighbouring the axial channel 16 for cloudy fine fraction, and a second distribution chamber 28 neighbouring the axial channel 3a for clear fine fraction. The free ends of the straight walls 24, 25, 26 are provided with axially extending plates 29a,29b, 29c, which are adjustable in the radial direction of the rotor shaft 2 for adjusting the gap between the cylindrical wall 4 and the respective straight walls 24, 25, 26, see Fig. 8. In the longitudinal direction, the distribution chambers 27, 28 are defined by two gable wails 30, 3i situated at opposite sides of the three filter discs 8, see Figs. 3 and 7. The gable walls 30, 31 are provided with adjustable sealing plates 32, 33.
Figs. 9 and 10 show a modification of the distribution chambers, wherein an additional chamber 34 is provided between the distri-bution chambers 27 and 28. In this case the partition wall means 15 shall be displaced somewhat upwardly by the adjustment means 20 so that the distribution chamber 27 receives a relatively clear fine fraction that is less clear than the corresponding relatively clear fine fraction obtainable in the embodiments of Figs. 1 to 8. In other words the distribution chamber 27 shall receive a fine fraction that could also be characterized as relatively cloudy. The distribution chambers 27,28,34 are defined longitudinally by two additional gable walls 35, 36 provided with sealing plates 37, 38. The additional gable walls 35, 36 encompass the three filter discs 6 and are situated a distance from the gable walls 30,31, respectively. As a result fine fraction, that may be relatively cloudy, escaping from chamber 27 past sealing plates 37, 38 can pass into the axial channel 16, as is indicated by arrows in Fig. 10, whereby relatively cloudy fine fraction is substantially prevented from escaping to the axial channel 3a via the sealing plates 32 and 33.
In operation, a suspension to be filtered is supplied to the container 1 through the inlet device 8, so that the container is filled with suspension normally to a level above said horizontal axis 5. The filter discs 6 are rotated by the drive motor 7, so that the peripheral chambers 13 are submerged one after the other into the suspension. With reference to Fig. 6, when a peripheral chamber 13 has moved downwardly to the position denoted by capital A, a cloudy fine fraction is forced by hydrostatic pressure through the filter material into chamber 13 while a mat of coarse particles is developed on the filter material. In the position denoted by capital B chamber 13 is filled with cloudy fine fraction, which begins to flow through the outlet 14 to the channel I6. now the mat on the filter material already is thick and tight enough to serve as a filter medium itself, whereby a clear fine fractior. is forced into the chamber 13 and is mixed with the cloudy fine fraction therein.
In the position denoted by capi~ai C chamber 13 contains cloudy fine fraction near the outlet 14, clear fine fraction near the filter material and relatively clear fine fraction there-between. ~n the position denoted by capital D all cloudy fine fraction should have left chamber 13, otherwise the adjustment means 20 is operated to adjust the position of the distribution chambers 27, 28 somewhat downwardly. In Fig. 6 angle a illustrates the sector of the central chamber 3 into which cloudy fine fraction is received. As the outlet 14 of chamber 13 passes the distribution chamber 27 the latter receives relatively clear fine fraction. In the position denoted by capital E clear fine fraction flows into the distribution chamber 28.
Since the pressures in the distribution chambers 27, 28 are substantially the same but stronger than the surroundings in the central chamber 3, the relatively clear fine fraction flowing into the distribution chamber 27 continues to flow through the gap between the cylindrical wall 4 and the plate 29a into the axial channel 16 for cloudy fine fraction, whereas the clear fine fraction flowing into the distribution chamber 28 continues to flow through the gaps between the cylindrical wall 4 and the plates 29c,32 and 33 into the axial channel 3a for clear fine fraction. Only an insignificant flow of clear fine fraction occurs from distribution chamber 28 to distribution chamber 27, because of the minor pressure difference between the two distri-bution chambers 27, 28.
With reference to Fig. 5, when a peripheral chamber 13 on the upwardly moving part of the filter disc 6 is in the position denoted by the capital F, the filter material of the chamber 13 is covered with a tight mat of coarse particles which is substantially liquid impervious. Since the outlet 14 of the chamber 13 opens into the pool 18 o~f fine fraction and the Iiauid content of the chamber I3 is above the surface ieve= 18a of . the pool, a negative pressure is created in the chamber 13.
As the chamber 13 moves further upwardly from position F and up above the sarface level of the suspension in the container 1 outside of the filter disc 6, said negative pressure in the chamber 13 increases. When the chamber 13 has reached the position denoted by the capital G, air is able to ente:: the pipe 21 from the central chamber 3 and be sucked by said negative pressure through the pipe 21 to the upper part of the chamber 13. As a result, the chamber 13 is emptied rapidly. When the chambe: 13 has moved from the position G to a zone in which the shower 10 is effective to knock off the high consistency mat of coarse particles from the filter material, so that the mat rolls off the filter material and passes into the outlet device 9, the chamber 13 is totally empty.
The arrangement of the venting means and the fine fraction distribution chambers according to the invention makes it possible in some applications to increase the rotationa2 speed of the filter discs by 100% or more, when filtering fibre pulp suspensions. Thus, the capacity of the apparatus of the invention is substantially increased.
EP-Bl-515492 discloses such an apparatus, which includes at least one annular vertical hollow filter disc having two opposed side walls of filter material and forming a central chamber.
Means is provided for rotating the annular filter disc about a horizontal axis extending centrally through the filter disc.
There are partition walls extending between the opposed side walls of the filter disc and positioned to divide the interior of the filter disc into a number of peripheral chambers disposed in series around the filter disc. Each peripheral chamber communicates with the central chamber via an outlet. The filter disc is adapted to be partly submerged in a body of a suspension to be filtered, such that the central chamber is at least partly submerged in said body of suspension, whereby a fine fraction of the suspension is forced by hydrostatic pressure through the side walls of filter material into the peripheral chambers and further into the central chamber via the outlets of the peripheral chambers. Means is provided to maintain a pool of fine fraction in the central chamber. The partition walls are arranged such that each peripheral chamber is at least partly above the pool of fine fraction at some point of the revolution of the filter disc at the upwardly moving part of the filter disc, while the outlet of the peripheral chamber opens into the pool of tine fraction.
The peripheral chambers of this known apparatus function as droplegs when they move upwardly, because at this stage of revolution the created mats of coarse particles covering the filter wall portions of the peripheral chambers are more or less liquid impervious. This has the advantage that the coarse fraction of the suspension is dewatered efficiently. This type of filter disc with integrated droplegs also eliminates the need for space demanding external droplegs.
However, a drawback to the apparatus of EP-B1-515492 is that the rotational speed of the disc is limited, because of the fact that each upwardly moving peripheral chamber has to be emptied before it reaches a knock-off zone, in which the mat is sprayed off the filter walls of the peripheral chamber. In the case of filtering a fibre pulp suspension of the kind which forms very tight fibre mats, so that air can only pass very slowly through the mat into the peripheral chambers, the rotational speed of the disc has to be particularly low which reduces the capacity.
The object of the present invention is to improve the filtering capacity of the type of apparatus disclosed in EP-B1-515492.
This object is- fulfilled by a filtering apparatus of the integrated dropleg type defined above, which is characterized by venting means effective to supply air into each peripheral chamber at the upwardly moving part of the filter disc, when the peripheral chamber is at least partly above the body of suspension during rotation of the filter disc, in order to speed up the emptying of the peripheral chamber.
Said supply of air into the peripheral chambers by the venting means can make the emptying of the peripheral chambers about two to three times faster, as compared with the known filtering apparatus. Therefore the rotational speed of the filter disc can be significantly increased to improve the filtering capacity of the apparatus.
The venting means is preferably adapted to supply the peripheral chambers with air from the central chamber. As an alternative, however, the venting means may comprise valves to the respective peripheral chambers adapted to open in a predetermined zone, through which the peripheral chambers pass during rotation of the filter disc, to allow air from outside the apparatus to enter the peripheral chambers.
The venting means may form venting passages extending from the central chamber into the respective peripheral chambers and preferably opening in the peripheral chambers proximate to the radially outermost and leading ends of the peripheral chambers, as seen in the direction of rotation of the filter disc. Each venting passage is inoperable as long as it does not communicate with the air above the pool of fine fraction in the central chamber. As soon as each peripheral chamber has moved upwardly to a position in which air can enter the venting passage associated to the peripheral chamber, the venting passage is operable to supply air into its peripheral chamber.
The venting passage of each peripheral chamber may open into the central chamber in advance of the outlet of the peripheral chamber, as seen in the direction of rotation of the filter disc, Which makes the function of the venting means particularly reliable.
In the most simplified embodiment of the apparatus of the invention, the venting means comprises pipes extending from the central chamber into the respective peripheral chambers to positions proximate to the leading ends of the peripheral chambers, as seen in the direction of rotation of the filter disc, whereby the interior of the pipes constitutes said venting passages.
The apparatus disclosed in EP-B1-515492 has means for separating the developed fine fraction into cloudy and clear fine fractions. Reference is also made to EP-H1-515502 disclosing said separating means in more detail. Said fine fraction separating means includes stationary rigid partition wall means extending axially in the central chamber and dividing the latter into at least two axial channels for receiving a cloudy fine fraction and a clear fine fraction, respectively. The central chamber is defined by a cylindrical wall and there is fine fraction discharge means for discharging said cloudy and clear fine fractions separately from the axial channels. The apparatus of the present invention may be designed likewise, if desired to obtain cloudy and clear fine fractions. However, it has been proven in practice that the increased rotational speed of the filter disc made possible by the above defined venting means results in an increased volume of mixed cloudy and clear fine fractions. To reduce said volume to at least some extent the partition wall means may be displaced forwards in the direction of rotation of the disc, provided that the resulted reduced flow of clear fine fraction from the apparatus is acceptable.
To allow such a fine fraction separating means to be incor-porated in the apparatus of the invention without being forced to restrict the rotational speed of the disc, so that the optimal flow of clear fine fraction can be obtained, the stationary partition wall means and the cylindrical wall define first and second distribution chambers. The first distribution chamber neighbours the axial channel for cloudy fine fraction and is adapted to receive relatively clear fine fraction flowing through the outlets of the peripheral chambers passing the first distribution chamber during rotation of the filter disc and to distribute said received relatively clear fine fraction to the axial channel f or cloudy fine fraction. The second distribution chamber neighbours the axial channel for clear fraction and is adapted to receive clear fine fraction flowing through the outlets of the peripheral chambers passing the second distri-bution chamber during rotation of the filter disc and to distribute said received clear fine fraction to the axial channel for clear fine fraction.
Since the pressures in the two distribution chambers are due to the heads between the body of suspension and the respective distribution chambers, the relatively clear fine fraction is forced from the first distribution chamber into the axial channel containing cloudy fine fraction. whereas substantially all of the clear fine fraction flowing into the second distri-bution chamber is forced into the axial channel containing clear fine fraction. Only a minor amount of clear fine fraction will pass from the second distribution chamber into the first distri-bution chamber, because of the small pressure difference between the two distribution chambers. Thus, the separation of cloudy and clear fractions can be made sharply, which enables a higher rotational speed of the filter disc, and consequently a larger flow of clear fine filtrate.
The invention is explained below in more detail by way of example with reference to the accompanying drawings, in which Figure 1 is a side view of an apparatus of the invention, Figure 2 is a sectional view along line II-II of Figure 1, Figure 3 is a part of a section along line III-III of Figure 2, Figure 4 is an enlarged view of a detail shown in Figure 1, Figure 5 is an enlarged vertical cross-section of an upwardly moving part of a filter disc for the apparatus of the invention, Figure 6 is a part of an enlarged sectional view along line VI-VI
of Figure 2, Figure 7 is a part of an enlarged sectional view along line VII-VII of Figure 2, Figure 8 is an enlarged detail of the embodiment shown in Figure 6, Figure 9 is a modification of the embodiment shown in Figure 8, and 'Figure 10 is a part of a longitudinal section along line X-X of Figure 9.
In Figures 1 and 2 there is shown an apparatus of the invention comprising a container 1 and a hollow rotor shaft 2, which forms a central chamber 3 with a cylindrical wall 4 which is journalled on the container 1, so that the shaft 2 is rotatable about a horizontal axis 5. Three annular vertical hollow filter discs 6 are mounted on the shaft 2 spaced from one another and are coaxial with the horizonta l axis 5. A drive motor 7 is connected to the shaft 2 and adapted to revolve the discs 6 in counter-clockwise direction, as shown in Fig. 1. An inlet device 8 is arranged to supply a suspension to be filtered to the container 1 at the downwardly moving side of the filter discs 6 and an outlet device 9 is located at the upwardly moving side of the filter discs 6 for receiving mats or cakes of coarse particles which are removed from the filter discs 6 by shower means 10.
Each filter disc 6 comprises two opposed side walls 11 of filter material. Partition walls 12 extend between the opposed side walls 11 and divide the interior of the filter disc into a plurality of peripheral chambers 13 (the number of chambers 13 may suitably be chosen from sixteen to twenty), the peripheral chambers 13 being disposed in series around the filter disc 6.
Each peripheral chamber 13 communicates with the central chamber 3 via an outlet 14 in the cylindrical wall 4.
In the central chamber 3 there is a means for separating developed fine fraction into cloudy and clear fine fractions.
This separation means comprises a stationary rigid partition wall means 15 dividing the central chamber 3 into an axial channel 16 for receiving cloudy fine fraction and an axial channel 3a for receiving clear fine fraction. The channel 16 extends axially along the central chamber 3 and out of the latter to an outlet device 17. Clear fine fraction is able to collect in channel 3a at the lower part of the central chamber 3 and to form a pool 18 of fine fraction therein. The level 18a of the surface of the pool 18 is determined by properly dimensioning the central chamber 3. As an alternative the level 18s may be determined by an adjustable overflow. The clear fine fraction collected in the axial channel 3a is discharged to an outlet device 19. The partition wall means 15 is turnable about said horizontal axis 5 and is connected to the container 1 by adjustment means 20 for adjusting the position of the partition wall means 15 in the central chamber 3.
Figure 5 shows the design of the peripheral chambers 13 in more detail on the upwardly moving part of the filter disc 6. Each chamber 13 is defined by two straight radially extending partition walls 12a and 12b, which at their radially innermost ends adjoin two backwardly extending slightly curved partition walls 12a' and 12b', as seen in the direcion of rotation. The radially innermost ends of the curved partition walls 12a', 12b' abut the cylindrical wall 4 at opposite sides of the outlet 14 of the peripheral chamber 13, so that the outlet 14 extends from the end of the lower curved partition wall 12b' but is spaced from the end of the upper curved partition wall 12a'.
Accordingly, there is a circumferential wall portion 4a of the cylindrical wall 4 between the outlet 14 and the end of the upper curved partition wall 12a'.
A venting means in the farm of a tube 21 extends from the central chamber 3 into each peripheral chamber 13 to a position proximate to the leading end 22 and the radially outermost part of the peripheral chamber 13. The interior of the tube 21 constitutes a passage 23 for supplying air from the central chamber 3 to the peripheral chamber 13. The tube 21 preferably extends through the wall portion 4a, but may alternatively have its lower end 21a directed to the outlet 14, suitably at the leading part of the outlet 14, as indicated in Fig. 5.
The stationary partition wall means 15 comprises three straight axially extending walls 24, 25, 25 having three longitudinal edges close to but spaced from the cylindrical wall 4 of the rotor shaft 2, at the downwardly moving part of the cylindrical wall 4, see Figs. 6 and 8. The walls 24, 25, 26 and the cylindrical wall 4 define a first distribution chamber 27 neighbouring the axial channel 16 for cloudy fine fraction, and a second distribution chamber 28 neighbouring the axial channel 3a for clear fine fraction. The free ends of the straight walls 24, 25, 26 are provided with axially extending plates 29a,29b, 29c, which are adjustable in the radial direction of the rotor shaft 2 for adjusting the gap between the cylindrical wall 4 and the respective straight walls 24, 25, 26, see Fig. 8. In the longitudinal direction, the distribution chambers 27, 28 are defined by two gable wails 30, 3i situated at opposite sides of the three filter discs 8, see Figs. 3 and 7. The gable walls 30, 31 are provided with adjustable sealing plates 32, 33.
Figs. 9 and 10 show a modification of the distribution chambers, wherein an additional chamber 34 is provided between the distri-bution chambers 27 and 28. In this case the partition wall means 15 shall be displaced somewhat upwardly by the adjustment means 20 so that the distribution chamber 27 receives a relatively clear fine fraction that is less clear than the corresponding relatively clear fine fraction obtainable in the embodiments of Figs. 1 to 8. In other words the distribution chamber 27 shall receive a fine fraction that could also be characterized as relatively cloudy. The distribution chambers 27,28,34 are defined longitudinally by two additional gable walls 35, 36 provided with sealing plates 37, 38. The additional gable walls 35, 36 encompass the three filter discs 6 and are situated a distance from the gable walls 30,31, respectively. As a result fine fraction, that may be relatively cloudy, escaping from chamber 27 past sealing plates 37, 38 can pass into the axial channel 16, as is indicated by arrows in Fig. 10, whereby relatively cloudy fine fraction is substantially prevented from escaping to the axial channel 3a via the sealing plates 32 and 33.
In operation, a suspension to be filtered is supplied to the container 1 through the inlet device 8, so that the container is filled with suspension normally to a level above said horizontal axis 5. The filter discs 6 are rotated by the drive motor 7, so that the peripheral chambers 13 are submerged one after the other into the suspension. With reference to Fig. 6, when a peripheral chamber 13 has moved downwardly to the position denoted by capital A, a cloudy fine fraction is forced by hydrostatic pressure through the filter material into chamber 13 while a mat of coarse particles is developed on the filter material. In the position denoted by capital B chamber 13 is filled with cloudy fine fraction, which begins to flow through the outlet 14 to the channel I6. now the mat on the filter material already is thick and tight enough to serve as a filter medium itself, whereby a clear fine fractior. is forced into the chamber 13 and is mixed with the cloudy fine fraction therein.
In the position denoted by capi~ai C chamber 13 contains cloudy fine fraction near the outlet 14, clear fine fraction near the filter material and relatively clear fine fraction there-between. ~n the position denoted by capital D all cloudy fine fraction should have left chamber 13, otherwise the adjustment means 20 is operated to adjust the position of the distribution chambers 27, 28 somewhat downwardly. In Fig. 6 angle a illustrates the sector of the central chamber 3 into which cloudy fine fraction is received. As the outlet 14 of chamber 13 passes the distribution chamber 27 the latter receives relatively clear fine fraction. In the position denoted by capital E clear fine fraction flows into the distribution chamber 28.
Since the pressures in the distribution chambers 27, 28 are substantially the same but stronger than the surroundings in the central chamber 3, the relatively clear fine fraction flowing into the distribution chamber 27 continues to flow through the gap between the cylindrical wall 4 and the plate 29a into the axial channel 16 for cloudy fine fraction, whereas the clear fine fraction flowing into the distribution chamber 28 continues to flow through the gaps between the cylindrical wall 4 and the plates 29c,32 and 33 into the axial channel 3a for clear fine fraction. Only an insignificant flow of clear fine fraction occurs from distribution chamber 28 to distribution chamber 27, because of the minor pressure difference between the two distri-bution chambers 27, 28.
With reference to Fig. 5, when a peripheral chamber 13 on the upwardly moving part of the filter disc 6 is in the position denoted by the capital F, the filter material of the chamber 13 is covered with a tight mat of coarse particles which is substantially liquid impervious. Since the outlet 14 of the chamber 13 opens into the pool 18 o~f fine fraction and the Iiauid content of the chamber I3 is above the surface ieve= 18a of . the pool, a negative pressure is created in the chamber 13.
As the chamber 13 moves further upwardly from position F and up above the sarface level of the suspension in the container 1 outside of the filter disc 6, said negative pressure in the chamber 13 increases. When the chamber 13 has reached the position denoted by the capital G, air is able to ente:: the pipe 21 from the central chamber 3 and be sucked by said negative pressure through the pipe 21 to the upper part of the chamber 13. As a result, the chamber 13 is emptied rapidly. When the chambe: 13 has moved from the position G to a zone in which the shower 10 is effective to knock off the high consistency mat of coarse particles from the filter material, so that the mat rolls off the filter material and passes into the outlet device 9, the chamber 13 is totally empty.
The arrangement of the venting means and the fine fraction distribution chambers according to the invention makes it possible in some applications to increase the rotationa2 speed of the filter discs by 100% or more, when filtering fibre pulp suspensions. Thus, the capacity of the apparatus of the invention is substantially increased.
Claims (11)
1. An apparatus for filtering mat forming suspensions, such as fibre pulp supensions including:
at least one annular vertical hollow filter disc (6) having two opposed side walls (11) of filter material and forming a central chamber (3);
means (7) for rotating the annular filter disc about a horizontal axis (5) extending centrally through the filter disc;
partition walls (12) extending between the oppposed side walls of the the filter disc and positioned to divide the interior of the filter disc into a number of peripheral chambers (13) disposed in series around the filter disc, each peripheral chamber communicating with the central chamber via an outlet (14), the filter disc being adapted to be partly submerged in a body of a suspension to be filtered, such that the central chamber is partly submerged in said body of suspension, whereby a fine fraction of the suspension is forced by hydrostatic pressure through the side walls of filter material into the peripheral chambers and further into the central chamber via the outlets of the peripheral chambers; and means for maintaining a pool (18) of fine fraction in the central chamber, the partition walls being arranged such that each peripheral chamber is at least partly above the pool of fine fraction at some point of the revolution of the filter disc at the upwardly moving part of the filter disc, while the outlet of the peripheral chamber opens into the pool of fine fraction;
characterized by venting means (21,23) effective to supply air from the central chamber (3) into each peripheral chamber (13) at the upwardly moving part of the filter disc (6), when the peripheral chamber is at least partly above the body of suspension during rotation of the filter disc, in order to speed up the emptying of the peripheral chamber.
at least one annular vertical hollow filter disc (6) having two opposed side walls (11) of filter material and forming a central chamber (3);
means (7) for rotating the annular filter disc about a horizontal axis (5) extending centrally through the filter disc;
partition walls (12) extending between the oppposed side walls of the the filter disc and positioned to divide the interior of the filter disc into a number of peripheral chambers (13) disposed in series around the filter disc, each peripheral chamber communicating with the central chamber via an outlet (14), the filter disc being adapted to be partly submerged in a body of a suspension to be filtered, such that the central chamber is partly submerged in said body of suspension, whereby a fine fraction of the suspension is forced by hydrostatic pressure through the side walls of filter material into the peripheral chambers and further into the central chamber via the outlets of the peripheral chambers; and means for maintaining a pool (18) of fine fraction in the central chamber, the partition walls being arranged such that each peripheral chamber is at least partly above the pool of fine fraction at some point of the revolution of the filter disc at the upwardly moving part of the filter disc, while the outlet of the peripheral chamber opens into the pool of fine fraction;
characterized by venting means (21,23) effective to supply air from the central chamber (3) into each peripheral chamber (13) at the upwardly moving part of the filter disc (6), when the peripheral chamber is at least partly above the body of suspension during rotation of the filter disc, in order to speed up the emptying of the peripheral chamber.
2. The apparatus of claim 1, wherein the venting means forms venting passages (23) extending from the central chamber (3) into the respective peripheral chambers (13).
3. The apparatus of claim 2, wherein the venting passages (23) open in the peripheral chambers (13) proximate to the leading ends of the peripheral chambers, as seen in the direction of rotation of the filter disc (6).
4. The apparatus of claim 3, wherein the venting passages (23) open in the peripheral chambers (13) proximate to the radially outermost ends of the peripheral chambers.
5. The apparatus of claim 2, wherein the venting passage (23) of each peripheral chamber (13) opens into the central chamber (3) in advance of the outlet (14) of the peripheral chamber, as seen in the direction of rotation of the filter disc.
6. The apparatus of claim 2, wherein the venting means (21,23) comprises pipes (21) extending from the central chamber (3) into the respective peripheral chambers (13) to positions proximate to the leading ends of the peripheral chambers, as seen in the direction of rotation of the filter disc (6), the interior of the pipes constituting said venting passages (23).
7. The apparatus of claim 6, wherein the pipes (21) extend to positions proximate to the radially outermost ends of the peripheral chambers (13).
8. The apparatus of claim 1, further including rigid stationary partition wall means (15) extending axially in the central chamber (3) and dividing the latter into at least two axial channels (27,28;34) for receiving a cloudy fine fraction and a clear fine fraction, respectively, the central chamber being defined by a cylindrical wall (4), and fine fraction discharge means (17,19) for discharging said cloudy and clear fine fractions separately from the two axial channels, the stationary partition wall means and the cylindrical wall defining first and second distribution chambers (27,28) situated between the two axial channels, the first distribution chamber (27) being adapted to receive relatively clear fine fraction flowing through the outlets (14) of the peripheral chambers passing the first distribution chamber during rotation of the filter disc (6) and to distribute said received relatively clear fine fraction to the axial channel (16) for cloudy fine fraction, the second distribution chamber (28) being adapted to receive clear fine fraction flowing through the outlets of the peripheral chambers passing the second distribution chamber during rotation of the filter disc and to distribute said received clear fine fraction to the axial channel (3a) for clear fine fraction.
9. The apparatus of claim 8, further including adjustment means (20) for adjusting the position of the first and second distribution chambers (27,28) in the circumferential direction of the cylindrical wall (4).
10. The apparatus of claim 9, wherein the partition wall means (15) is turnable about said horizontal axis (5) by the adjustment means (20).
11. The apparatus of claim 8, wherein each distribution chamber (27,28) has an extension in the circumferential direction of the cylindrical wall (4) which is at least equal to that of the outlet (14) of each peripheral chamber (13).
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9703139A SE9703139D0 (en) | 1997-09-01 | 1997-09-01 | Apparatus for filtering suspensions |
| SE9703139-7 | 1997-09-01 | ||
| PCT/SE1998/001542 WO1999011357A1 (en) | 1997-09-01 | 1998-08-31 | Apparatus for filtering suspensions |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2301164A1 true CA2301164A1 (en) | 1999-03-11 |
Family
ID=20408095
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002301164A Abandoned CA2301164A1 (en) | 1997-09-01 | 1998-08-31 | Apparatus for filtering suspensions |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JP2001514067A (en) |
| AU (1) | AU9012898A (en) |
| CA (1) | CA2301164A1 (en) |
| DE (1) | DE19882626T1 (en) |
| FI (1) | FI20000452A (en) |
| SE (1) | SE9703139D0 (en) |
| WO (1) | WO1999011357A1 (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI70526C (en) * | 1984-12-03 | 1986-09-24 | Enso Gutzeit Oy | SKIVFILTER |
| US5330646A (en) * | 1990-02-16 | 1994-07-19 | Ingenjorsfirman R. Frykhult Ab | Apparatus for filtering liquids |
-
1997
- 1997-09-01 SE SE9703139A patent/SE9703139D0/en unknown
-
1998
- 1998-08-31 JP JP2000508449A patent/JP2001514067A/en active Pending
- 1998-08-31 CA CA002301164A patent/CA2301164A1/en not_active Abandoned
- 1998-08-31 WO PCT/SE1998/001542 patent/WO1999011357A1/en active Application Filing
- 1998-08-31 DE DE19882626T patent/DE19882626T1/en not_active Withdrawn
- 1998-08-31 AU AU90128/98A patent/AU9012898A/en not_active Abandoned
-
2000
- 2000-02-28 FI FI20000452A patent/FI20000452A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| AU9012898A (en) | 1999-03-22 |
| DE19882626T1 (en) | 2000-08-24 |
| FI20000452A (en) | 2000-02-28 |
| JP2001514067A (en) | 2001-09-11 |
| SE9703139D0 (en) | 1997-09-01 |
| WO1999011357A1 (en) | 1999-03-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |