CA1335191C - Screening method and apparatus for light reject removal - Google Patents
Screening method and apparatus for light reject removalInfo
- Publication number
- CA1335191C CA1335191C CA000594419A CA594419A CA1335191C CA 1335191 C CA1335191 C CA 1335191C CA 000594419 A CA000594419 A CA 000594419A CA 594419 A CA594419 A CA 594419A CA 1335191 C CA1335191 C CA 1335191C
- Authority
- CA
- Canada
- Prior art keywords
- rotor
- screen
- duct
- light
- reject
- 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.)
- Expired - Fee Related
Links
- 238000012216 screening Methods 0.000 title claims abstract description 33
- 238000000034 method Methods 0.000 title claims description 7
- 239000007788 liquid Substances 0.000 claims abstract description 19
- 238000010790 dilution Methods 0.000 claims abstract description 16
- 239000012895 dilution Substances 0.000 claims abstract description 16
- 239000000835 fiber Substances 0.000 claims abstract description 12
- 230000001105 regulatory effect Effects 0.000 claims abstract description 5
- 239000012535 impurity Substances 0.000 claims description 6
- 238000000926 separation method Methods 0.000 claims description 5
- 239000002657 fibrous material Substances 0.000 claims description 3
- 238000007599 discharging Methods 0.000 claims description 2
- 238000005406 washing Methods 0.000 claims description 2
- 239000004033 plastic Substances 0.000 description 14
- 229920003023 plastic Polymers 0.000 description 14
- 239000002245 particle Substances 0.000 description 7
- 239000000463 material Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 239000000725 suspension Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 2
- 238000007865 diluting Methods 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 229920001131 Pulp (paper) Polymers 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
- 239000001913 cellulose Substances 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- JTJMJGYZQZDUJJ-UHFFFAOYSA-N phencyclidine Chemical class C1CCCCN1C1(C=2C=CC=CC=2)CCCCC1 JTJMJGYZQZDUJJ-UHFFFAOYSA-N 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 229910021653 sulphate ion Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- 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
- D21D5/023—Stationary screen-drums
- D21D5/026—Stationary screen-drums with rotating cleaning foils
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
- B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
- B01D29/117—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements arranged for outward flow filtration
- B01D29/118—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements arranged for outward flow filtration open-ended
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
- B01D29/76—Handling the filter cake in the filter for purposes other than for regenerating
- B01D29/86—Retarding cake deposition on the filter during the filtration period, e.g. using stirrers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
- B01D29/88—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor having feed or discharge devices
- B01D29/94—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor having feed or discharge devices for discharging the filter cake, e.g. chutes
- B01D29/945—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor having feed or discharge devices for discharging the filter cake, e.g. chutes for continuously discharging concentrated liquid
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
- B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
- B07B1/18—Drum screens
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
- B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
- B07B1/18—Drum screens
- B07B1/22—Revolving drums
- B07B1/24—Revolving drums with fixed or moving interior agitators
Abstract
A screen for fibre pulp is provided with means for removal of light reject. The screening apparatus comprises a vertical cylindrical screen (2); and a rotor (3) which is concentrically disposed inside the screen and the substantially closed outer surface (9) of which together with the inner surface (10) of the screen defines a screen-ing zone (11) for the pulp. A duct (19) is provided inside the rotor (3) the upper end of the duct being disposed adjacent to the inner surface (21) of the closed upper end (12) of the rotor (3). The duct (19) is provided with valve means (32) for regulating the discharge of the light rejects and further provided with branch pipe (30) for introducing dilution liquid to the duct (19) and further to the rotor inner space. There are valve means (31) arranged in connection with the branch pipe (30) for regulating the dilution liquid flow to the duct (19).
Description
Screenlng method and apparatus for llght reject removal The present inventlon relates to a screening method and apparatus for separatlng solld particles, such as fibre bundles and llght partlcles from flbrous slurries used in paper making. The apparatus malnly comprises a substantially vertical cylindrical screen, a substantially cylindrical rotor concentrically arranged thereln, said rotor and said screen defining a screenlng zone for the pulp, an accept chamber surrounding the outer surface of said screen, an inlet for supplying the pulp to be screened into the upper end of said screening zone, a re~ect chamber connected to the lower end of sald screenlng zone and means for separating the heavy and the light impurities from each other inside said rotor. The method comprises introducing dilution liquid close to the top cover of the rotor inside the rotor for separatlng and washing the light reject off from the heavier reJect, flber bundles, knots etc.
When screening paper pulps contalnlng a variety of impurities in a screen described e.g. in U.S. patent no.
3,363,759, the re~ect contalns also partlcles which can be separated therefrom by employlng centrifugal force. The particles separated in this way, the specific gravity of which is lower than that of the average particles, i.e.
the light reject, contains e.g. various plastics. The remaining reject contains e.g. fibre bundles and pieces of knots. It is an ob~ect of the present invention to provide a screening apparatus which in a simple manner separates light impurities from the reject. The reason for removing light rejects, e.g. plastics from the reject flow is the fact that plastics etc. are very harmful in paper making processes. The reject from screening apparatuses is usually recirculated through grinding devices back to the screening apparatuses for recovering all the fibers from fiber bundles in such a way that the light re~ects, like plastics, are ~' also ground whereby they wlll be small enough to be accepted by the screens and they end up to the paper machine and thus lower the quality of the end product.
The screening apparatus in which the present invention is a remarkable improvement has been developed from a known screen disclosed e.g. in U.S. patent 3,363,759. An improved version of the screeni ng apparatus of the above patent has later been modified for removal of plastics, said apparatus in turn being disclosed in U.S. patent 3,912,622. In this version the separation of the light particles from the rejected pulp is arranged through a pipe one end of which is fixed to the inlet end of the screen and the other end extended through an opening in the cover of the casing. A
conical extention is provided in the other end of the pipe which extends to the open upper end of the rotor. Due to the vortex movement of the reJected pulp the light reject concentrated in the lnner part of the vortex flows out through a discharge pipe while the heavier reject gathered in the outer part is recirculated into the screening zone.
In order to achieve efficient separation the reject flow must be ample which decreases the capacity of the machine.
The screening apparatus on which the present invention is based comprises a substantially vertical cylindrical screen, a substantially cylindrical rotor which is concentrically disposed inside the screen and the substantially closed outer surface of which together with the interior surface of the screen defines a screening zone for the pulp, an accept chamber surrounding the outer surface of the screen, an inlet for supplying the pulp to be screened into the upper end of the screening zone, a reject chamber connected to the lower end of the screening zone, and means for separating the heavy and the light impurities from each other inside the rotor.
Said means for separating the heavy and the light impurities i.e. reject fractions is a duct that extends from outside the apparatus through the bearing support lnslde the rotor close to the top cover of the rotor. Sald screening apparatus is more closely described in US patent 4,634,521.
It is an object of the present invention to provide an arrangement ln connectlon with the device of said US patent 4,634,521 for further improving the separation of light rejectable material from the re~ect. It has been found important to decrease the amount of light rejects as much as possible as usually the llght rejects are discharged from the screening apparatus to a tank for further processing.
The further processlng ls necessary for recovering the fiber materlal being discharged with the light rejects as the rejected lighter materlal normally contains about 90 %
fiber material that could be recirculated back to the system. Sald further processlng usually means a separate sorting arrangement wlth screening devices and perhaps even cyclones for separatlng the llght rejects, most often plastics, from the acceptable flber material. By using the improvement of the present lnventlon lt is possible, in the most advantageous clrcumstances, to discharge the llght reJect, malnly plastlcs, totally without any need to reclrculate lt to further screenlng. Thls is achieved by lmprovlng the ablllty of the apparatus to separate light reject from flbre bundles, sllves, knots etc. in such a way that the fibre bundles, knots etc. do not enter the discharge duct for the light rejects. It has been found out that the light reJects, mainly plastics, are able to separate themselves from the cellulosic material if the consistency of the suspension ls low enough. Now, by lntroducing the dllution liquid close to the top cover of the rotor inside the rotor, the consistency of the suspension is lowered just where it is needed. Now that the consistency is lowered the plastics and like rejects tend to float on the liquid/suspension thus filling the space under the top cover of the rotor. The simplest way of doing that ls to lead the dilution liquid through the same duct upwards whlch duct iQ used for removing the llght re~ects.
Thls ls made possible by arranging a branch pipe having a valve in connection with the duct leading inside the rotor for removing the light re~ect. Said branch pipe is preferably arranged outside the screening apparatus housing close to the valve in the duct for discharging the light reject between said valve and the screening apparatus housing.
The present invention provides a reliable way for removing light re~ect in a pro-environmental manner.
The apparatus according to the invention is illustrated by the accompanying drawing which ls described in detail below.
Figure 1 is a vertical section of an embodiment of the lnventlon.
The maln components of the screen lllustrated in Figure 1 are a multi-compartment houslng l, a substantially cylindrical screen drum 2, a substantially cyolindrical rotor 3 and a shaft 4. The shaft is rotatably mounted inside the rotor on bearings on a cylindrical support 5 which is fixed to the housing by a sealing ~oint. The rotor is mounted on the upper end of the shaft and a belt pulley 6 on the lower end of the shaft for rotating the rotor. A disc 7 is fixed to the upper end of the support through which the shaft extends. The rotor outer surface 9 provided in a preferred embodiment with e.g. half-spheri-cal protrusions 8 and the inner surface 10 of theconcentric screen drum define a ring-shaped screening zone ll where the pulp to be screened ls fed into. The upper end of the rotor is closed by a top cover 12 into which the shaft is fixed.
The upper part of the housing constitutes of a feed chamber 13 provided with an inlet connection 14 for the pulp to be screened. There is a re~ect chamber 15 provided with a ;~
dlscharge connection 16 in the lower part of the housing.
The upper end of the screening zone 11 is connected to the feed chamber and the lower end to the reject chamber.
There is an accept chamber 17 outslde the screen drum.
An inlet 18 for dilution liquid may be arranged in the reject chamber. A discharge duct l9, which extends through the support and the disc 7 in the upper end of the support, is disposed inside the support; the upper end of the duct is disposed adjacent to the inner surface 21 of the rotor top cover 12.
The pulp to be screened is supplied into the device through the inlet connection 14 and at first it circulates in the feed chamber tangentially. The feed chamber acts at the same time as a scrap catcher, where stones and other heavy particles are removed. From the feed chamber the pulp flows into the ring-shaped channel ll between the rotor 3 and the screen drum 2 functioning as a screening zone.
The accept flows from the screening zone 11 through the screen surface 10 to the accept chamber 17. From the accept chamber the pulp is discharged through a discharge connection 20.
The reject, i.e the portion of the pulp flow which does not pass through the screen surface, ends up in the reject chamber 15. In the reject chamber the reject may be diluted by dilution liquid supplied through the opening 18 and is discharged through the discharge connection 16.
Several mill scale test have shown that e.g. the plastics, which is a typical constituent in the light reject, remains on the reject side. E.g. by employing a 0.45 mm slot screen as the screening surface, 85 to 95 ~ of the plastics in a typical sulphate cellulose pulp can be removed, which yields accept with a plastics content of 5 to 15 ~ , only, of the plastics content of the feed flow. The problem that led to the invention of US 4,634,521 was how to separate the plastics and other llght partlcles from the reJect flow that ls to be reclrculated as explalned above.
The solution ls slmple and efflclent. The llght reject flows lnto a space 22 inslde the rotor through the rotor bottom end 23. The high revolution speed, which is typical to the rotor, brings the pulp in the screening space, in the re~ect chamber and in the space 22 inside the rotor into a rotating motlon which creates the centrifugal force necessary for the separation of the light reJect. Dilution liquid may be supplied into the re~ect chamber in order to regulate the consistency.
In the apparatus in accordance with said US patent the light reject is gathered inside the rotor 3 in the space under the top cover 12 wherefrom lt may be removed through duct l9 either continuously or intermittently. The only two problems with the gathered llght reject when uslng the apparatus in accordance wlth sald US patent are that the separated light re~ect contalns plenty of fiber material that could well be used and that the duct 19 easily become~
blocked when the conslstency of the re~ect is too high.
The solution to the flrst problem ls dllutlng the reject lnside the rotor in such a way that the light rejects have space enough to rise upwards and separate from the fibrous particles. The most effective way of dllutlng ls to lead the dilution llquid close to the top cover of the rotor so that the light rejects will remaln floatlng on the liquid and the coarser re~ects, flber bundles etc. will be washed off from the light re~ects whereby the liquid flowing slowly downwards takes the fiber bundles and knot particles. The solution to the second problem is arranging the dilution through duct 19 in such a way that the dilution liquid slowly flows through said duct to the top of the rotor compartment malntalning the duct clean. For regulating the flows of the diluting liquid and the light rejects the branch pipe 30 is provided with valve means 31 and the ~' dlscharge duct 19 with valve means 32. Said valve means are used in such a way that the valve 32 is for the most of the time closed and the valve 31 open letting the diluting liquid to flow throught the duct inside the rotor.
After e.g. four hours the valve 31 in the branch pipe is closed and valve 32 in the duct 19 opened so that the plastics etc. are able to flow away from inside the rotor.
After few minutes the valve 32 is closed and valve 31 opened whereby the dilution starts again. In a mill scale test the reJects discharged through duct 19 without the branch pipe arrangement contained 300 - 500 kgs fiber per day. After the branch pipe with the valve arrangement having been installed the amount of fibers in the re~ects dropped to 30 - 50 kgs fiber per day.
It is of course clear that the pulp may also be partially diluted at the bottom end of the screening zone by liquid supplied through the dilution water ring. There may be openings in the rotor through which the main portion of the re~ect flow is supplied into the space inside the rotor where the light re~ect is separated by centrifugal force. The light reJect flows up lnto the space under the rotor top cover, is diluted/washed there and is removed therefrom through the discharge duct from time to time and the remaining re~ect flows down lnto the re~ect chamber from whlch lt is discharged through the opening.
The present invention ls not limited to the embodiments above said embodiments being presented and described as examples only, but several modifications may be made thereof within the scope of protection defined by the appended claims.
k~
When screening paper pulps contalnlng a variety of impurities in a screen described e.g. in U.S. patent no.
3,363,759, the re~ect contalns also partlcles which can be separated therefrom by employlng centrifugal force. The particles separated in this way, the specific gravity of which is lower than that of the average particles, i.e.
the light reject, contains e.g. various plastics. The remaining reject contains e.g. fibre bundles and pieces of knots. It is an ob~ect of the present invention to provide a screening apparatus which in a simple manner separates light impurities from the reject. The reason for removing light rejects, e.g. plastics from the reject flow is the fact that plastics etc. are very harmful in paper making processes. The reject from screening apparatuses is usually recirculated through grinding devices back to the screening apparatuses for recovering all the fibers from fiber bundles in such a way that the light re~ects, like plastics, are ~' also ground whereby they wlll be small enough to be accepted by the screens and they end up to the paper machine and thus lower the quality of the end product.
The screening apparatus in which the present invention is a remarkable improvement has been developed from a known screen disclosed e.g. in U.S. patent 3,363,759. An improved version of the screeni ng apparatus of the above patent has later been modified for removal of plastics, said apparatus in turn being disclosed in U.S. patent 3,912,622. In this version the separation of the light particles from the rejected pulp is arranged through a pipe one end of which is fixed to the inlet end of the screen and the other end extended through an opening in the cover of the casing. A
conical extention is provided in the other end of the pipe which extends to the open upper end of the rotor. Due to the vortex movement of the reJected pulp the light reject concentrated in the lnner part of the vortex flows out through a discharge pipe while the heavier reject gathered in the outer part is recirculated into the screening zone.
In order to achieve efficient separation the reject flow must be ample which decreases the capacity of the machine.
The screening apparatus on which the present invention is based comprises a substantially vertical cylindrical screen, a substantially cylindrical rotor which is concentrically disposed inside the screen and the substantially closed outer surface of which together with the interior surface of the screen defines a screening zone for the pulp, an accept chamber surrounding the outer surface of the screen, an inlet for supplying the pulp to be screened into the upper end of the screening zone, a reject chamber connected to the lower end of the screening zone, and means for separating the heavy and the light impurities from each other inside the rotor.
Said means for separating the heavy and the light impurities i.e. reject fractions is a duct that extends from outside the apparatus through the bearing support lnslde the rotor close to the top cover of the rotor. Sald screening apparatus is more closely described in US patent 4,634,521.
It is an object of the present invention to provide an arrangement ln connectlon with the device of said US patent 4,634,521 for further improving the separation of light rejectable material from the re~ect. It has been found important to decrease the amount of light rejects as much as possible as usually the llght rejects are discharged from the screening apparatus to a tank for further processing.
The further processlng ls necessary for recovering the fiber materlal being discharged with the light rejects as the rejected lighter materlal normally contains about 90 %
fiber material that could be recirculated back to the system. Sald further processlng usually means a separate sorting arrangement wlth screening devices and perhaps even cyclones for separatlng the llght rejects, most often plastics, from the acceptable flber material. By using the improvement of the present lnventlon lt is possible, in the most advantageous clrcumstances, to discharge the llght reJect, malnly plastlcs, totally without any need to reclrculate lt to further screenlng. Thls is achieved by lmprovlng the ablllty of the apparatus to separate light reject from flbre bundles, sllves, knots etc. in such a way that the fibre bundles, knots etc. do not enter the discharge duct for the light rejects. It has been found out that the light reJects, mainly plastics, are able to separate themselves from the cellulosic material if the consistency of the suspension ls low enough. Now, by lntroducing the dllution liquid close to the top cover of the rotor inside the rotor, the consistency of the suspension is lowered just where it is needed. Now that the consistency is lowered the plastics and like rejects tend to float on the liquid/suspension thus filling the space under the top cover of the rotor. The simplest way of doing that ls to lead the dilution liquid through the same duct upwards whlch duct iQ used for removing the llght re~ects.
Thls ls made possible by arranging a branch pipe having a valve in connection with the duct leading inside the rotor for removing the light re~ect. Said branch pipe is preferably arranged outside the screening apparatus housing close to the valve in the duct for discharging the light reject between said valve and the screening apparatus housing.
The present invention provides a reliable way for removing light re~ect in a pro-environmental manner.
The apparatus according to the invention is illustrated by the accompanying drawing which ls described in detail below.
Figure 1 is a vertical section of an embodiment of the lnventlon.
The maln components of the screen lllustrated in Figure 1 are a multi-compartment houslng l, a substantially cylindrical screen drum 2, a substantially cyolindrical rotor 3 and a shaft 4. The shaft is rotatably mounted inside the rotor on bearings on a cylindrical support 5 which is fixed to the housing by a sealing ~oint. The rotor is mounted on the upper end of the shaft and a belt pulley 6 on the lower end of the shaft for rotating the rotor. A disc 7 is fixed to the upper end of the support through which the shaft extends. The rotor outer surface 9 provided in a preferred embodiment with e.g. half-spheri-cal protrusions 8 and the inner surface 10 of theconcentric screen drum define a ring-shaped screening zone ll where the pulp to be screened ls fed into. The upper end of the rotor is closed by a top cover 12 into which the shaft is fixed.
The upper part of the housing constitutes of a feed chamber 13 provided with an inlet connection 14 for the pulp to be screened. There is a re~ect chamber 15 provided with a ;~
dlscharge connection 16 in the lower part of the housing.
The upper end of the screening zone 11 is connected to the feed chamber and the lower end to the reject chamber.
There is an accept chamber 17 outslde the screen drum.
An inlet 18 for dilution liquid may be arranged in the reject chamber. A discharge duct l9, which extends through the support and the disc 7 in the upper end of the support, is disposed inside the support; the upper end of the duct is disposed adjacent to the inner surface 21 of the rotor top cover 12.
The pulp to be screened is supplied into the device through the inlet connection 14 and at first it circulates in the feed chamber tangentially. The feed chamber acts at the same time as a scrap catcher, where stones and other heavy particles are removed. From the feed chamber the pulp flows into the ring-shaped channel ll between the rotor 3 and the screen drum 2 functioning as a screening zone.
The accept flows from the screening zone 11 through the screen surface 10 to the accept chamber 17. From the accept chamber the pulp is discharged through a discharge connection 20.
The reject, i.e the portion of the pulp flow which does not pass through the screen surface, ends up in the reject chamber 15. In the reject chamber the reject may be diluted by dilution liquid supplied through the opening 18 and is discharged through the discharge connection 16.
Several mill scale test have shown that e.g. the plastics, which is a typical constituent in the light reject, remains on the reject side. E.g. by employing a 0.45 mm slot screen as the screening surface, 85 to 95 ~ of the plastics in a typical sulphate cellulose pulp can be removed, which yields accept with a plastics content of 5 to 15 ~ , only, of the plastics content of the feed flow. The problem that led to the invention of US 4,634,521 was how to separate the plastics and other llght partlcles from the reJect flow that ls to be reclrculated as explalned above.
The solution ls slmple and efflclent. The llght reject flows lnto a space 22 inslde the rotor through the rotor bottom end 23. The high revolution speed, which is typical to the rotor, brings the pulp in the screening space, in the re~ect chamber and in the space 22 inside the rotor into a rotating motlon which creates the centrifugal force necessary for the separation of the light reJect. Dilution liquid may be supplied into the re~ect chamber in order to regulate the consistency.
In the apparatus in accordance with said US patent the light reject is gathered inside the rotor 3 in the space under the top cover 12 wherefrom lt may be removed through duct l9 either continuously or intermittently. The only two problems with the gathered llght reject when uslng the apparatus in accordance wlth sald US patent are that the separated light re~ect contalns plenty of fiber material that could well be used and that the duct 19 easily become~
blocked when the conslstency of the re~ect is too high.
The solution to the flrst problem ls dllutlng the reject lnside the rotor in such a way that the light rejects have space enough to rise upwards and separate from the fibrous particles. The most effective way of dllutlng ls to lead the dilution llquid close to the top cover of the rotor so that the light rejects will remaln floatlng on the liquid and the coarser re~ects, flber bundles etc. will be washed off from the light re~ects whereby the liquid flowing slowly downwards takes the fiber bundles and knot particles. The solution to the second problem is arranging the dilution through duct 19 in such a way that the dilution liquid slowly flows through said duct to the top of the rotor compartment malntalning the duct clean. For regulating the flows of the diluting liquid and the light rejects the branch pipe 30 is provided with valve means 31 and the ~' dlscharge duct 19 with valve means 32. Said valve means are used in such a way that the valve 32 is for the most of the time closed and the valve 31 open letting the diluting liquid to flow throught the duct inside the rotor.
After e.g. four hours the valve 31 in the branch pipe is closed and valve 32 in the duct 19 opened so that the plastics etc. are able to flow away from inside the rotor.
After few minutes the valve 32 is closed and valve 31 opened whereby the dilution starts again. In a mill scale test the reJects discharged through duct 19 without the branch pipe arrangement contained 300 - 500 kgs fiber per day. After the branch pipe with the valve arrangement having been installed the amount of fibers in the re~ects dropped to 30 - 50 kgs fiber per day.
It is of course clear that the pulp may also be partially diluted at the bottom end of the screening zone by liquid supplied through the dilution water ring. There may be openings in the rotor through which the main portion of the re~ect flow is supplied into the space inside the rotor where the light re~ect is separated by centrifugal force. The light reJect flows up lnto the space under the rotor top cover, is diluted/washed there and is removed therefrom through the discharge duct from time to time and the remaining re~ect flows down lnto the re~ect chamber from whlch lt is discharged through the opening.
The present invention ls not limited to the embodiments above said embodiments being presented and described as examples only, but several modifications may be made thereof within the scope of protection defined by the appended claims.
k~
Claims (6)
1. A screening apparatus comprising a substantially vertical cylindrical screen (2); a rotor (3) which is concentrically disposed inside the screen and substantially closed outer surface (9) of which together with the interior surface (10) of the screen defines a screening zone (11) for the pulp; an accept chamber (17) surrounded by the outer surface of the screen; an inlet opening (14) for supplying the pulp to be screened into the upper end of the screening zone; a reject chamber (15) connected to the lower end the screening zone: and means (23) for separating the heavy and the light impurities from each other, wherein a duct (19) is disposed inside the rotor (3) to remove light reject, the upper end of said duct being located adjacent to the inner surface (21) of the top cover (12) of the rotor the improvement further comprising means for providing the upper end space of the rotor with dilution liquid for maintaining the consistency of the reject low enough for effective separation of light rejects from fibrous material.
2. A screen as recited in claim 1 wherein said means is a duct (19) arranged to extend through a bearing support (5) disposed inside the rotor close to the top cover of the rotor.
3. A screen as recited in claim 1 wherein said means is a duct used also for removing the light rejects said duct being provided with valve means for regulating the flow of the light rejects.
4. A screen as recited in claim 3 wherein said duct is provided with a branch pipe for introducing the dilution liquid to said duct.
5. A screen as recited in claim 4 wherein the branch pipe is provided with valve means for regulating the flow of the dilution liquid.
6. A method for separating light rejects from the reject flow of a screening apparatus of pulp and paper industry said method comprising introducing said reject flow inside a rotor of said screening apparatus, allowing said reject flow circulate on the rotor inner wall whereby the light rejects are gathered close to the axis of the rotor, introducing dilution liquid close to the top cover of the rotor for lowering the consistency of the rejects and for washing the light rejects off from the fiber bundles, shives, knots etc. and discharging the light rejects from the nearhood of the rotor top cover.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000594419A CA1335191C (en) | 1989-03-22 | 1989-03-22 | Screening method and apparatus for light reject removal |
| JP1074803A JPH0327192A (en) | 1989-03-22 | 1989-03-27 | Screen, filtering method and filter |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000594419A CA1335191C (en) | 1989-03-22 | 1989-03-22 | Screening method and apparatus for light reject removal |
| JP1074803A JPH0327192A (en) | 1989-03-22 | 1989-03-27 | Screen, filtering method and filter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1335191C true CA1335191C (en) | 1995-04-11 |
Family
ID=25672540
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000594419A Expired - Fee Related CA1335191C (en) | 1989-03-22 | 1989-03-22 | Screening method and apparatus for light reject removal |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH0327192A (en) |
| CA (1) | CA1335191C (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001040570A1 (en) * | 1999-11-29 | 2001-06-07 | Andritz Oy | Arrangement and rotor for screening of pulp |
| WO2017158228A1 (en) * | 2016-03-16 | 2017-09-21 | Red Wire Oy | Method for screening and a screening apparatus |
| CN108166301A (en) * | 2017-12-26 | 2018-06-15 | 郑州运达造纸设备有限公司 | A kind of multi-functional pressure sieves rotor structure |
| CN117127425A (en) * | 2023-09-22 | 2023-11-28 | 安德里茨（中国）有限公司 | Coarse screening system |
-
1989
- 1989-03-22 CA CA000594419A patent/CA1335191C/en not_active Expired - Fee Related
- 1989-03-27 JP JP1074803A patent/JPH0327192A/en active Granted
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001040570A1 (en) * | 1999-11-29 | 2001-06-07 | Andritz Oy | Arrangement and rotor for screening of pulp |
| WO2017158228A1 (en) * | 2016-03-16 | 2017-09-21 | Red Wire Oy | Method for screening and a screening apparatus |
| US10738420B2 (en) | 2016-03-16 | 2020-08-11 | Red Wire Oy | Method for screening and a screening apparatus |
| CN108166301A (en) * | 2017-12-26 | 2018-06-15 | 郑州运达造纸设备有限公司 | A kind of multi-functional pressure sieves rotor structure |
| CN108166301B (en) * | 2017-12-26 | 2023-08-18 | 郑州运达造纸设备有限公司 | Multifunctional pressure screen rotor structure |
| CN117127425A (en) * | 2023-09-22 | 2023-11-28 | 安德里茨（中国）有限公司 | Coarse screening system |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0418076B2 (en) | 1992-03-26 |
| JPH0327192A (en) | 1991-02-05 |
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