WO2004046457A1 - Procede et appareil de traitement d'une suspension fibreuse - Google Patents

Procede et appareil de traitement d'une suspension fibreuse Download PDF

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Publication number
WO2004046457A1
WO2004046457A1 PCT/FI2003/000881 FI0300881W WO2004046457A1 WO 2004046457 A1 WO2004046457 A1 WO 2004046457A1 FI 0300881 W FI0300881 W FI 0300881W WO 2004046457 A1 WO2004046457 A1 WO 2004046457A1
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WO
WIPO (PCT)
Prior art keywords
rotor
recited
rejects
fiber suspension
screening cavity
Prior art date
Application number
PCT/FI2003/000881
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English (en)
Inventor
Pentti Ahlqvist
Original Assignee
Advanced Fiber Technologies (Aft) Oy
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 Advanced Fiber Technologies (Aft) Oy filed Critical Advanced Fiber Technologies (Aft) Oy
Priority to AU2003283443A priority Critical patent/AU2003283443A1/en
Publication of WO2004046457A1 publication Critical patent/WO2004046457A1/fr

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Classifications

    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21DTREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
    • D21D5/00Purification of the pulp suspension by mechanical means; Apparatus therefor
    • D21D5/02Straining or screening the pulp
    • D21D5/023Stationary screen-drums
    • D21D5/026Stationary screen-drums with rotating cleaning foils

Definitions

  • the present invention relates to a method and apparatus for treating fiber suspensions of the pulp and paper industry.
  • the method according to the invention is particularly suitable in screening pulps of the wood processing industry.
  • the apparatus according to the invention relates to a novel rotor construction for a pressure screen.
  • the pressure screens in their simplest form, comprise a normally vertically oriented, though also horizontal and inclined devices have been used, substantially cylindrical housing having one inlet duct, and two outlet ducts, one for the accepted fraction, i.e. the so called accept, and one for the rejected fraction, i.e. the so called reject.
  • the housing surrounds a screen drum having openings for sorting the fiber suspension, which is introduced in the pressure screen.
  • the openings of the screen drum may be round or oblong holes, or slots.
  • the screen drum may be manufactured either by machining said openings into a metal plate, which is then bent to form a circular screen drum, or by attaching a number of screen wires side by side leaving a narrow gap between the wires so that the gap forms the screening opening.
  • a rotor attached to a rotatable shaft of the pressure screen. Normally the rotor is arranged inside the screen drum, but there are also applications where the rotor is outside the screen drum, or where the screen drum itself is rotatable.
  • the rotor has several purposes.
  • One purpose is to produce pressure pulses towards the screen drum, or screen openings to force acceptable fiber material through the screen openings.
  • Another purpose is to create a suction pulse that draws material away from the screen drum. This is especially important in case the screen openings tend to be blocked by reject material, or by thickened fiber suspension.
  • Yet another purpose is to mix the fiber suspension in the vicinity of the screen drum, as the fiber suspension tends to thicken in front of the screen openings after acceptable fibers and water have passed the screen openings. In other words, the longer the suspension stays between the rotor and the screen drum the more the consistency of the fiber suspension increases.
  • the open rotors have, normally, substantially radial arms attached to the rotary shaft, and a so-called foil or wing or blade attached to the end of the arms (see, for instance, US 4,193,865). Normally there are two arms for each foil, one arm close to the upper end of the foil, and another arm close to the lower end of the foil. The orientation of the foil is most often axial, though also somewhat twisted foils have been used.
  • the closed rotors (for instance US 3,437,204 or US 5,176,261) have either a substantially cylindrical shell extending substantially to the entire height, or length, of the screen drum, or a dome-shaped shell (US 4,642,189, or 4,679,982, or US 4,749,475), which also extends to the entire height of the screen drum.
  • other closed rotor types like for instance EP-A2-1124003 with its hourglass- shaped rotor. All these closed rotor types have so called turbulence elements on their surface facing the screen drum. The purposes of such elements are the same as that of the foil i.e.
  • rotor types that have properties from both basic rotor types. For instance, there are rotors having foils attached by means of short arms on a cylindrical rotor shell, and rotors having impeller like rotors, which do not leave entirely the interior of the rotor open.
  • the pressure screens function in the following manner. Fresh fiber suspension, or pulp, or stock is introduced into the pressure screen housing via an inlet duct. Normally the fiber suspension is in a pressurized state. The fiber suspension is guided between the rotor and the screen drum. In other words, depending on the rotor type, the fiber suspension fills either the cavity between the rotor shell and the screen drum, or between the rotor shaft and the screen drum. The fiber suspension, which is in communication with the rotor, starts slowly to rotate in said cavity along the screen drum while it also flows, normally downwards, towards the lower end, or in broader terms, the rejects area of the pressure screen.
  • the fibers move freely in the suspension and end up into the screen openings, and after having passed through the screen openings the fibers form the accept fraction of the screen.
  • the turbulence elements of the rotor mix the reject fraction and keep it in movement, which prevents the clogging of the screen and its openings.
  • the presence of the rejected material on the screen surface, or even in the vicinity of the screen surface lowers the screening efficiency.
  • US-A-5,000,842 discloses a rotor structure, a closed one, where the rotor surface is provided with turbulence members having a specifically designed leading surface. Till the publication of the above-mentioned patent the turbulence members had been similar all over the rotor surface. Now, the shape of leading surface of the turbulence members is dictated by the axial position of the turbulence member.
  • the turbulence members being positioned close to the upper, in- feed end of the rotor have a leading surface, whose purpose is to 'pump' the suspension downwards. I.e. the leading surface of the turbulence member is inclined such that it subjects the pulp to a downwardly directed force component.
  • the leading surface of the turbulence members is plow-like, i.e. having a substantially radial leading edge and two wings on both sides thereof. However, the wings are still dimensioned so that the turbulence member subjects the fraction remaining in the screening cavity to a force component directed downwards.
  • the turbulence elements are substantially neutral, i.e.
  • the fraction can be called rejects, as it contains for the most part particles that are not able to pass through the screen openings, to a force component directed upwards.
  • rejects the fraction contains for the most part particles that are not able to pass through the screen openings, to a force component directed upwards.
  • the purpose of the above-described function is partially to get the screen surface into more efficient use by forcing pulp downwards between the rotor and the screen, i.e. in the screening cavity, and partially to feed the rejects downward so that they do not lower down the screening efficiency at the upper zones of the rotor.
  • the patent discloses a closed rotor structure, where the suspension is fed to the gap between a screen surface and a rotor, and accepts flow through openings in the screen surface. Rejects continue along the filter surface to a rejects outlet. Relative rotation is effected between the screen surface and the rotor.
  • the suspension at the screen surface is coarser and/or of higher solids concentration than the accepts.
  • This coarser suspension is removed from the screen surface by means of a guide plate, which is arranged in the flow direction after the turbulence member i.e. at the backside of the turbulence member.
  • the guide plate 'scrapes' the reject from the screen surface and moves it towards the rotor surface.
  • a backwardly inclined plate arranged axially below the turbulence member forces fresh suspension toward the filter surface to take the place of the rejects just moved away from the surface.
  • the apparatus comprises an outer casing with conduits for inlet pulp, accepts, heavier rejects and lighter rejects, respectively; a screen cylinder and a rotor, the surface of which is provided with at least one protrusion; and an opening for guiding the light rejects through the surface of the rotor.
  • the US document teaches the removal of the rejects from the screening cavity through the rotor shell inside the rotor.
  • the dome-shaped rotors approach the problem from another point of view.
  • US-A- 4,697,982 a rotary pressure pulp screening device is disclosed.
  • the screening device provides a streamlined flow of pulp and one of its objects is to supply a fairly constant velocity of pulp along the length of the screen thus utilizing its full length.
  • a cylindrical housing is included with a cylindrical screen therein, a rotary impeller mounted for rotation about an axis within the screen, the impeller having a body with an inlet end substantially in line with a fixed disc ring forming part of the housing, and an outlet end adjacent the upstream end of the cylindrical screen, the body having a shape with a circular axial cross section from the inlet end to the outlet end thus leaving a larger annular space at the inlet end representing an annular inlet between the disc ring and the body of the impeller, and impeller blades radiating from at least a portion of the body of the impeller and extending to within a short distance from the screen for the length of the screen.
  • the improvement discussed in the patent comprises at least one substantially frusto-conical shaped baffle, concentric with the body of the impeller, extending from the annular inlet, adapted to divide a flow of pulp entering the annular inlet and direct the divided flows to different locations along the pulp screen height.
  • US 4,915,822 Another structure resulting in a similar operation is discussed in US 4,915,822, where a method and an apparatus for treating a fiber suspension are disclosed.
  • the fiber suspension is fed into a treatment apparatus having treatment zones and divided into two fractions, an accept and a reject, the reject being guided from one zone behind at least one adjacent treatment zone to a separate reject treatment zone, in which the remaining accept of the suspension is discharged.
  • the apparatus being divided into a plurality of axial zones and having a rotor and at least one screen arranged in an outer housing, and in the treatment space between the screen and the rotor, members are arranged for guiding the suspension from the different treatment zones of the treatment space to the separate reject treatment zone.
  • the US document teaches the feeding of fresh pulp to a zone below the topmost zone of the screen cylinder. In fact an operation similar to that of the dome-shaped rotors is thus also discussed.
  • FI 70614 discussed a screen for fiber material, provided with means for diluting the pulp in a screening space between the rotor and the screen drum.
  • the cited reference discloses that the dilution is carried out by means of pressurized liquid from a conventional source of pressurized liquid.
  • WO 93/23609 and WO 01/40570 discuss feeding of dilution liquid through the rotor surface into the screening space.
  • the publications teach that the dilution liquid is introduced in a separate piping from outside the rotor and the whole screen to the inside of the rotor and further to the screening space.
  • EP 933468 discloses a solution of its own for treating fiber suspension in a screen. According to the solution of the publication, fresh fiber suspension is introduced into the screen having an open, so-called foil rotor and the suspension is screened in the ordinary manner after which dilution water is added to the reject and the diluted reject is re-introduced to screening.
  • the present invention discusses a novel method and apparatus for optimising the screening.
  • a purpose of the invention is to make it possible to limit the increase in the consistency to a manageable level, i.e. to a level, curve B, Fig. 2, where the acceptable fibers can still be separated from the rejects with acceptable energy consumption.
  • Yet another object of the invention is to make it possible to effectively treat the reject fraction so that minimal amount of fiber material enters the final rejects of the screen.
  • One of the characterizing features of the method in accordance with the present invention is the forced feeding of fiber suspension from inside the rotor into the screening cavity through a substantially closed rotor for diluting said rejects in said screening cavity.
  • One of the characterizing features of the apparatus in accordance with the present invention is that the rotor is provided with means for feeding forcibly fiber suspension from inside said rotor into the screening cavity through said substantially closed rotor for diluting said rejects in said screening cavity.
  • the specific energy consumption (kW/accepted tons of pulp) is decreased, as the consistency at the reject area of the screening cavity is limited to an acceptable value.
  • the amount of rejects is reduced, as the lower screening consistency at the reject area of the screening cavity makes the screening more efficient.
  • the amount of accepts is increased for the same reason, and also due to possible recycling of the rejects fraction.
  • the entire operation of the pressure screen is more stable as the changes in consistency are smaller.
  • the lower screening consistency allows the use of smaller screening slits or openings resulting in cleaner accept flow.
  • Fig. 1 illustrates schematically a pressure screen in accordance with prior art
  • Fig. 2 is a graphical illustration of the operation of a prior art pressure screen compared with the pressure screen of the invention
  • Figs. 3a and 3b illustrate an apparatus in accordance with a preferred embodiment of the present invention
  • FIGs. 4a - 4d illustrate details of an apparatus in accordance with a few preferred embodiments of the present invention
  • Fig. 5 illustrates an apparatus in accordance with one more preferred embodiment of the invention
  • Figs. 6a - 6c illustrate a few rotor structures in accordance with a few preferred embodiments of the invention.
  • the prior art pressure screen illustrated schematically by Fig. 1 includes a substantially cylindrical outer housing 2, which is normally positioned vertically, but can also be positioned horizontally, or inclined.
  • the housing 2 has an inlet 4 for the pulp or fiber suspension to be screened, and an outlet 6 for the accepted fibers, and an outlet 8 for the rejects.
  • the housing 2 is closed at the top end by means of a cover 10, and at the bottom end thereof by means of a bottom cover 12.
  • the housing encircles a rotating member, a so-called rotor 14, whose shaft 16 is supported to the bottom cover by means of bearings and a sealing 18.
  • a screen cylinder or drum 20 is arranged at a distance outside the rotor 14 so that a screening cavity 22 is formed therebetween.
  • accepts space 24 from where the accepts flow into the accepts outlet 6.
  • rejects space 26 into which the rejects collect before being discharged from the apparatus.
  • the rotor shown in Fig. 1 is a so-called closed rotor, which means, in this case, that the rotor has a rotationaily symmetric outer surface and a cover, which prevents any fresh fiber suspension from entering inside the rotor.
  • closed rotor means, in this case, that the rotor has a rotationaily symmetric outer surface and a cover, which prevents any fresh fiber suspension from entering inside the rotor.
  • a rotor which has a substantially solid shell, which may only have a limited number of openings therethrough.
  • An opposite rotor structure would be an 'open rotor', which is, for instance, understood to mean a so called foil rotor.
  • Fig. 2 shows how the consistency changes in the screening cavity in front of the screening openings along the length of the screening cavity.
  • the X-axis illustrates the consistency c of the fiber suspension in the screening in %
  • the Y-axis the length L of the screen drum, or the screening cavity, being measured from the rejects end thereof towards the infeed end thereof.
  • Curve A shows how the consistency increases steadily from the top of the screening cavity to the bottom thereof in the prior art apparatus.
  • Curve B illustrates the change in the consistency in an apparatus in accordance with the invention.
  • the present invention discloses a substantially closed rotor, which functions, basically, in a similar manner as the above discussed prior art rotor.
  • the rotor of the invention is designed such that some fresh fiber suspension is allowed to flow inside the rotor so that said fresh fiber suspension may be fed through openings in the rotor shell to appropriate positions into the screening cavity to dilute the thickened fiber suspension therein.
  • Curve B shows how the consistency increases somewhat at the top end of the screening cavity until the consistency is limited, by means of the above- described dilution, to a certain value. Said value represents the consistency at which the screening can still be performed efficiently, i.e. where acceptable fibers can be separated from the rejectable material with sufficient accuracy.
  • the rotor surface is provided with openings 30 through its shell.
  • the openings 30 can be round holes, rectangular or oblong openings, or slots, just to name a few possible shapes of openings.
  • the inside rotor surface is provided with scoops 32 for guiding fiber suspension towards the openings 30, and through the openings 30 into the screening cavity outside the rotor 114.
  • the scoop 32 of Fig. 3b is formed of substantially planar elements.
  • An inclined back plate 34 is attached to the rotor inner surface behind, or downstream of the opening 30 in such a manner that it covers the opening 30 at least partially when seen in radial direction.
  • the scoop of Fig. 3b has a top plate 36, which in this embodiment is substantially circumferentially oriented.
  • the height of the top plate or in broader terms, the height of the scoop in general, measured from the rotor inner surface may be from 30 to 100 mm depending on the size of the rotor, for instance.
  • the scoop 32 has, preferably, two side plates 38, which close the space between the rotor inner surface and the back plate 34, and the top plate 36.
  • the side plates may be parallel or they may leave a wedge shaped cavity therebetween.
  • the side plates 38 together with the top plate 36 and the rotor inner surface leave a passage 40 to the inside of the scoop 32, said passage extending further into the opening 30. In case the side plates form a wedge shaped cavity, the cavity is as largest at the opening into the passage.
  • An essential feature of the scoop is that either the angle ⁇ between the scoop element back plate 34 attached to the downstream ( referring to the direction of rotation of the rotor) side of the opening 30, and the rotor inner surface across the opening is sharp, or the scoop itself is positioned at least partially above the opening, i.e. the back plate may be positioned at right angles to the rotor inner surface but the top plate extends in the direction of rotation of the rotor to cover the opening at least partially.
  • Another essential feature of the scoop is that the passage 40 opens substantially in the direction of the rotation of the rotor. Said passage 40 may also widen in the rotational direction of the rotor, but such is not necessary.
  • arrows C show the rotational direction of the rotor.
  • Both of said essential features of the scoop relate to the function of the scoop whereby it is, in fact, the functionality that dictates what, for instance, is meant by 'substantially in the direction of rotation of the rotor'. It means that the direction into which the scoop passage opens has to be such that the fiber suspension finds it way into the passage and that its velocity can be diverted in radial direction.
  • the substantially closer rotor is meant a rotor, which has less than 60 % of its surface provided with openings.
  • the total open area of the rotor could vary from about 10 % to about 60 % of the total surface area of the rotor.
  • the screening efficiency is not mainly dictated by the speed of the fresh pulp hitting the screen surface, but the pressure difference across the screen drum and the turbulence available. Only in limited areas of the screen surface the thickened fiber suspension is subjected to sprays of diluting fiber suspension, which dilutes the thickened suspension and simultaneously brings new fiber suspension in the screening cavity.
  • the scoop 32 functions so that while the rotor 114 is rotating the fiber suspension inside the rotor is not rotating at all or at least not at the same speed as the rotor whereby there is a certain velocity difference between the rotor and the pulp.
  • the speed of the fiber suspension is from 30 to 60% of the speed of the rotor.
  • the scoop catches the pulp into the passage 40 and forces the pulp through the opening 30 into the screening cavity.
  • the scoop diverges the velocity difference, which is normally in circumferential direction, to a substantially radial direction forcing the pulp into the screening cavity at a speed capable of overcoming the possibly relatively high back pressure in the screening cavity.
  • Figs. 4a to 4d show different embodiments for the scoops.
  • the scoop 132 of Fig. 4a is substantially similar to the scoop 32 of Fig. 3b, though the angular position of the back plate and the length of the top plate have been somewhat changed.
  • the scoop 232 of Fig. 4b has only the inclined back plate, and side plates.
  • the scoop 332 of Fig. 4c is a curved one in such a manner that the scoop 332 runs along the edges of the opening 30, at the backside thereof. Also planar back and top plates have been replaced with one curved element.
  • Fig. 4d shows a somewhat different scoop, as it could be formed of a pipe bend attached to the sides of the opening 30.
  • the pipe can have a varying area of cross-section so that the area is at its largest at the inlet end of the pipe and the smallest at the opening 30.
  • This kind of a scoop is used for collecting fresh fiber suspension from farther away from the rotor surface, whereby the radial position of its inlet end may be adjusted at whatever feasible distance from the rotor inner surface.
  • the scoop may have a number of variations whereby, for instance, a planar element attached to the downstream side of the rotor opening and bent above the opening should be considered as a simple form of a scoop. Also, a planar element similarly attached to the downstream side of the opening but at a sharp angle with the rotor inner surface so that the element leans above the opening, is another simple form of a scoop. Further, a scoop may also be formed of two such bent or inclined leaning planar elements set in a V-form to the downstream side of the opening.
  • Fig. 5 illustrates yet another preferred embodiment of the invention. In fact it is a novel way of using the scoops inside the rotor.
  • Fig. 5 shows a pressure screen in a manner similar to Fig. 1. The same components have been given the same reference numeral.
  • the rotor of Fig. 5 has been cut along a plane running along its axis so that the scoops 632 and 652 inside the rotor 614 can be seen.
  • the scoops 652 may be used to recycle the reject fraction at the reject end of the rotor 614.
  • Fig. 5 shows how the scoops 652 have been arranged at the lower end of the rotor 614, and arrows R show the circulation of the rejects from the screening cavity round the rotor skirt inside the rotor 614 and from there via the scoops 652 into the screening cavity 22. This operation is due to the pressure difference the scoops 652 create.
  • the scoops 652 By efficiently drawing pulp from inside the rotor 614 and feeding such forcibly into the screening cavity 22 the scoops 652 create a pressure difference between the screening cavity 22 and the rejects space 626 below the rotor 614, as well as a similar pressure difference between the rejects space 626, and the interior of the rotor 614. In this way part of the reject fraction is made to return to the screening cavity 22 whereby said fraction will be screened again, and some acceptable material can be recovered from the fraction rejected once already.
  • the above-described function may be made more efficient by, simultaneously with the feeding of the reject fraction, feeding dilution liquid either along with the reject fraction or separately therefrom to the screening cavity 22.
  • the recyclable reject fraction may be diluted at an appropriate point prior to feeding it back to the screening cavity.
  • the dilution liquid may be in this reject dilution case, either low consistency fiber suspension, fresh fiber suspension having a lower consistency, black liquor, some filtrates from the pulp or paper making process or fresh water, just to name a few alternatives from a number of possible liquids that can be used for dilution.
  • the purpose is to lower the consistency of the fiber suspension in the screening cavity, and do that at least in connection with feeding fiber suspension into said screening cavity.
  • the easiest way to add dilution liquid to the screening cavity is to feed fresh pulp with the recycled reject fraction into said cavity 22 by means of scoops 652.
  • Another exemplary alternative would be to bring dilution liquid along the rotor shaft, and lead such further towards the screening cavity by means of the arms (not shown) carrying the rotor. Further, yet another option would be to introduce dilution liquid to the screening cavity from outside the screen drum, for instance, by arranging a dilution liquid pipe extending through the accepts volume, and opening into the screening cavity at the inner surface of the screen drum.
  • FIG. 6 illustrates a few preferable embodiments for the rotor inner structure. The rotor illustrations shown this far have been very schematic with the exception of the more detailed scoop structures. Now Figs. 6a, 6b, and 6c show how the inside of the rotor can be provided with different means for aiding the operation of the rotor - scoop combination.
  • Fig. 6a discloses a rotor 714 being open at the top, or in more general terms at the inlet end of the rotor so that fresh pulp may flow freely inside the rotor 714.
  • the rotor surface is provided with scoops 732 as discussed earlier in this specification.
  • the rotor is further provided with a baffle 760 being of either conical (as shown) or of other appropriate (cylindrical, dome-shaped etc.) shape.
  • An object of the baffle is to close a substantial part of the cross-sectional area of the rotor so that the flow of fresh pulp within the rotor can be controlled.
  • the baffle 760 is at the lower end of the rotor 714, i.e.
  • the baffle 760 may be directly fastened to the shaft of the rotor or by means of an annular plate, for instance.
  • the purpose of the baffle and the annular plate/s is to limit the flow of fresh pulp inside the rotor so that all the fresh pulp may be fed via the scoops into the screening cavity. By means of the baffle 760 it is possible to adjust the height to which fresh pulp can be introduced.
  • Fig. 6b discloses a substantially similar rotor 814 having an open inlet end and an open rejects end.
  • the baffle 860 has been arranged perpendicular to the axis of the rotor 814.
  • the baffle 860 could have other orientations, too. For instance, it could be conically shaped.
  • the baffle has been attached to the shaft 816 of the rotor 814 at a certain distance from the rejects end of the rotor. By doing this the recycling of the reject fraction, as discussed in connection with Fig. 5, has been ensured.
  • the baffle 860 is provided with openings 864 for allowing fresh pulp from the infeed end of the rotor to flow into the rejects end of the rotor.
  • the fresh pulp at the inside of the rejects end of the rotor is used for diluting the circulated reject fraction while it is fed by means of scoop 852 into the screening cavity.
  • Fig. 6c illustrates an improvement to the embodiment of Fig. 6b.
  • the opening 864 of the baffle 860 is provided with a scoop 966, which takes fresh pulp from the infeed end of the rotor 914, and leads it directly to the scoop 952 at the rejects end of the rotor 914. While the scoop 952 is primarily intended for feeding the recycled reject fraction back to the screening cavity, it now receives fresh pulp along scoop 966 for diluting the reject fraction.
  • the description of the invention does not illustrate, describe or even list all possible variations of the pressure screen, screen drum, or the rotor as the invention is applicable in all kinds of pressure screen and filters having a rotating rotor having a member moving within a fiber suspension or pulp to be screened.
  • the pressure screen may be installed in any possible orientation.
  • the axis thereof may be vertical, horizontal, or inclined.
  • the inlet and outlet openings of the pressure screen may be directed to any appropriate direction and the number of them is not necessarily limited to only one.
  • the screen drum can be made either by perforating a plate of appropriate material, most often metal, or by arranging wires side by side to form a so called wedge-wire screen.
  • Said perforations may, for instance, be round or oblong holes or lengthy slits.
  • Said wires may be arranged in axial direction whereby the sorting or screening slots are positioned in axial direction, too. They may form so called hoops which are stacked on top of each other whereby the screening slits are in a direction perpendicular to the screen drum axis. Or the wires may be arranged spirally whereby the screening slots left between the adjacent wires will also be spiral.
  • the invention can be applied to any possible type of screen.
  • the pulp can be fed not only to the other end of the screen but also to the center or any other axial section of the screen drum, whereby the rejects may be collected from both ends of the screen drum.
  • the claims discuss generally about the infeed area and the rejects area meaning the area, where fiber suspension is introduced into the rotor, and the area, where the rejects are concentrated prior to removal from the screening cavity, respectively.
  • These areas should be understood as axially oriented sections of the screen, whereby also the inside of the rotor, which may contain substantially fresh pulp, belongs to the rejects area if, in the screening cavity, it is a question of a final phase of the screening, i.e. a phase where the relative amount of rejects is very high just prior to the removal of the rejects from the screening cavity.
  • the invention also covers screen drums having a non-cylindrical shape.
  • the screen drum may be frusto-conical or formed of two frusto-conical parts attached together, just to name a couple of alternatives.
  • the- general shape of the rotor may be freely chosen.
  • the rotor may be of cylindrical, frusto-conical, conical, hourglass, dome or some other appropriate shape.
  • the only prerequisite for the rotor is that the scoops according to the invention may be fastened to the inner surface of the rotor shell so that they function in a manner described earlier in this description.
  • the rotor outer surface may have whatever type of turbulence elements for ensuring favourable screening conditions in the screening cavity.
  • the rotor may also be formed of only one or several parts attached on the same shaft, the combined axial length of which, however, equals to at least 50% of the axial length of the screen drum.

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Abstract

La présente invention se rapporte à un procédé et à un appareil permettant de traiter des suspensions fibreuses de l'industrie des pâtes et papiers. L'invention se caractérise en ce que ladite suspension fibreuse est entraînée par force depuis l'intérieur du rotor vers une cavité de criblage par l'intermédiaire d'un rotor sensiblement fermé afin que soit diluée une fraction de rejet dans ladite cavité de criblage au moyen d'une écope (32) comportant une ouverture de passage (40) dans le sens de rotation du rotor.
PCT/FI2003/000881 2002-11-19 2003-11-19 Procede et appareil de traitement d'une suspension fibreuse WO2004046457A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003283443A AU2003283443A1 (en) 2002-11-19 2003-11-19 Method and apparatus for treating fiber suspension

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20022055 2002-11-19
FI20022055A FI20022055A (fi) 2002-11-19 2002-11-19 Menetelmä ja laite kuitususpension käsittelemiseksi

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WO2004046457A1 true WO2004046457A1 (fr) 2004-06-03

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FI (1) FI20022055A (fr)
WO (1) WO2004046457A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20130001151A1 (en) * 2010-03-16 2013-01-03 Jouko Hautala Pressure filter
EP3212840A4 (fr) * 2014-10-31 2018-04-11 Valmet AB Procédé et agencement pour dilution de décharge
US20220349124A1 (en) * 2021-04-30 2022-11-03 Andritz (China) Ltd. Pressure Screen and Method for Dilution for a Pressure Screen

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE437040B (sv) * 1979-03-29 1985-02-04 Gauld Equip Mfg Anordning for silning av fibrost material
EP0294832A2 (fr) * 1987-06-11 1988-12-14 A. Ahlstrom Corporation Appareil pour l'épuration de pâte

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE437040B (sv) * 1979-03-29 1985-02-04 Gauld Equip Mfg Anordning for silning av fibrost material
EP0294832A2 (fr) * 1987-06-11 1988-12-14 A. Ahlstrom Corporation Appareil pour l'épuration de pâte

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20130001151A1 (en) * 2010-03-16 2013-01-03 Jouko Hautala Pressure filter
US9085851B2 (en) * 2010-03-16 2015-07-21 Jouko Hautala Pressure filter
EP3212840A4 (fr) * 2014-10-31 2018-04-11 Valmet AB Procédé et agencement pour dilution de décharge
US20220349124A1 (en) * 2021-04-30 2022-11-03 Andritz (China) Ltd. Pressure Screen and Method for Dilution for a Pressure Screen
US11926961B2 (en) * 2021-04-30 2024-03-12 Andritz (China) Ltd. Pressure screen and method for dilution for a pressure screen

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FI20022055A (fi) 2004-05-20
FI20022055A0 (fi) 2002-11-19

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