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
  • D21D5/18—Purification of the pulp suspension by mechanical means; Apparatus therefor with the aid of centrifugal force
  • D21D5/22—Purification of the pulp suspension by mechanical means; Apparatus therefor with the aid of centrifugal force in apparatus with a vertical axis
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04C—APPARATUS USING FREE VORTEX FLOW, e.g. CYCLONES
  • B04C3/00—Apparatus in which the axial direction of the vortex flow following a screw-thread type line remains unchanged ; Devices in which one of the two discharge ducts returns centrally through the vortex chamber, a reverse-flow vortex being prevented by bulkheads in the central discharge duct
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04C—APPARATUS USING FREE VORTEX FLOW, e.g. CYCLONES
  • B04C3/00—Apparatus in which the axial direction of the vortex flow following a screw-thread type line remains unchanged ; Devices in which one of the two discharge ducts returns centrally through the vortex chamber, a reverse-flow vortex being prevented by bulkheads in the central discharge duct
  • B04C3/06—Construction of inlets or outlets to the vortex chamber
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/66—Pulp catching, de-watering, or recovering; Re-use of pulp-water

Definitions

• the present invention relates to a process and an apparatus for sorting a fibre suspension by separation of a relatively lighter and a relatively heavier fraction by means of centrifugation.
• the invention relates to the use of said process and apparatus for the cleaning of papermaking stock in the wet end short circulation of a paper machine.
• the function of cleaners widely used in the pulp and paper industries can be optimized and made more efficient so that the fibre losses remain small and the cleaning effi ⁇ ciency high while cleaning the stock in one single cleaning stage.
• Cleaners known in the prior art are usually conical vessels, into the larger end of which the material to be cleaned is fed tangentially. A heavier fraction is removed from the narrower end of said vessel and a lighter fraction is removed centrally from the larger part of said vessel.
• the material can be split into two fractions, or in other words, either heavy particles can be removed from the suspension and rejected, or light particles, as for example plastics, may be removed.
• a cleaned pulp suspension is obtained from the other outlet.
• the cleaners are susceptible to wear due to the fast movement and high g-forces of sand and other heavy material along their surface, the huge number of cleaners lead to an increase of the damage sensi- tivity and maintenance need for the whole cleaning plant.
• Said cleaner consists of an essentially cylindrical rotating chamber, in which the light frac ⁇ tion moves to a vacuum zone forming in the center of said chamber and the heavy fraction moves towards the mantle of said rotating chamber.
• the light fraction is removed from the center of the separator either at its inlet end or from the outlet end opposite to the inlet end and the heavy fraction collecting at the mantle is removed from the periphery of the chamber.
• a separate liquid is fed along the mantle of the apparatus, which liquid dilutes the suspension collecting at the mantle, washing out lighter components from the heavier fraction.
• the object of the present invention is to avoid the inconveniences of the prior art and to provide a technically well functioning apparatus, with an excellent separation efficiency and sorting capability.
• the object is to improve the function of cleaning systems used in the pulp and paper industry so, that instead of the prior use of multiple consecutive cleaners, the cleaning can be made efficiently in one single apparatus, so that the suspension can be fed through one cleaner rapidly while saving energy and effectuating repeated washing of the heavier fraction integratedly during the cleaning process.
• acceptable fibres are continually separated from the already separated heavy fraction and from the already separated light fraction and transferred into the accept flow constituted by the intermediary fraction.
• the invention is particularly favorable for the use in the short circulation of a paper web forming process, where a controlled stock dilution and fast recirculating can provide an essential improvement of the process.
• the object of the invention is a centrifugal separator for the sorting of a fibre suspension, said separator comprising an essentially cylindrical housing at one end of which is arranged a feeding inlet for fibre suspension to be cleaned, and at the opposite end of which there are outlets for a lighter fraction and a heavier fraction.
• a coaxial hollow rotating rotor is arran ⁇ ged for receiving said fibre suspension or an essential part of the same, that the mantel of said rotor has slots or openings, through which a part of said suspension can be brought to pass from a space inside said rotor mantle to a space outside, and from said space outside said rotor to said space inside, and that said separator has means for introducing a dilution and washing medium into said suspension for improving the separation efficiency between said ligh ⁇ ter and said heavier fractions.
• said dilution and washing medium is fed close to the mantle of said housing in multiple places.
• a tube is arranged coaxially in the center of said rotor acting as a sorting channel, for separating a light fraction.
• said fibre suspension is fed through an essentially cylindrical housing in said separator and said suspension is caused to rotate in said separator so that said suspension due to a centrifugal force is separated according to the density of its components into at least two fractions.
• Said process comprises the steps wherein a) said fibre suspension is fed into the inlet end of said separator; b) said suspension flow or a substantial part thereof is caused to pass into a hollow rotor rotating coaxially inside said cylindrical housing; c) the heavier fraction of said suspension is brought to move toward the mantle of said rotor; d) the heavier fraction accumulating at said mantle of said rotor is conducted out from said rotor into a space between said rotor and said housing to form a heavy fraction; e) a dilution / washing medium is introduced into said heavy fraction; f) a lighter subfraction of said heavy fraction in said space between said rotor and said housing is conducted into the lighter fraction in said rotor; g) at least a part of the stages c) to f) is repeated if needed; and h) said heavy fraction cumulating outside said rotor at said housing and said lighter fraction cumulating inside said rotor are separately discharged from said separator.
• an inject suspen ⁇ sion is divided into three fractions, an intermediate accept fraction constituting the main suspension flow.
• a heavy fraction and a light fraction constituting heavy and light reject, respectively, are separated from said suspension.
• a lighter subfraction is separated from said heavy fraction and a hea ⁇ selfish subfraction is separated from said light fraction, the two subfractions being brought back into said intermediate fraction.
• said heavy fraction is collected outside said rotor and said light fraction is collected inside a central tube installed inside said rotor.
• Fig. 1 represents a schematic section of a centrifugal separator according to a preferred embodiment of the invention
• Figs. 2 to 7 represent sections of the centrifugal separator according to Fig 1 , along lines A-A, B-B, C-C, D-D, E-E and F-F correspondingly;
• Fig. 8 represents a schematic section of a centrifugal separator according to another embodiment of the invention.
• Fig. 9 represents a flow sheet of a papermaking process in which the use of the invention is particularly preferred.
• the separator 10 has an essen ⁇ tially cylindrical housing 12 and in one end 14 of said separator an inlet 1 6 for the suspension to be cleaned. In the opposite end 1 8 of said separator 10 there is an outlet 20 for the lighter fraction and correspondingly an outlet 22 for the heavier fraction.
• a hollow rotating rotor 24 which functions as the principal sorting channel 25 for the fibre suspension.
• said rotor is cylindrical and its mantle has slots 26, which permit part of the suspension flowing in sorting channel 25 to flow into the space 28 between rotor 24 and housing 1 2 which space forms a channel for the heavy fraction.
• the edges of channels 26 and 30 are shaped to form oblique smoothly streamlined channels in the desired direction of suspension flow.
• the rotor 24 can also be of a different than cylindrical shape, for example a polygon, whereby openings for letting the lighter fraction pass into the sorting channel 25 in the rotor are arranged in the parts of the edged mantle closest to the center of the separator 10.
• openings for letting the heavy fraction separating from the intermediate fraction in channel 25 pass into the heavy fraction channel outside the rotor are arranged in the parts most distant from the center of the edged rotor.
• the mantle of rotor 24 consists of multiple cylindrical parts, between which the slots 26, 36 remain.
• the cylind ⁇ rical parts are united by radial separation walls 31 seen in Fig 5.
• feeding pipes 32 for dilution and/or washing liquid which in the presented embodiment are formed as annular inlets 35, through which liquid can be evenly distributed into the heavy fraction accumulating close to the inner surface of housing 12.
• a laminar zone forms and retains lighter material, which forms a lighter subfraction and flows with the liquid into sorting channel 25 through slots 26, whereas heavy material transfers the laminar layer, accumulating at the inner surface of the housing.
• the fluid fed through feeding pipes 32 may, preferably, be water, like backwater recycled from the process.
• the fluid may also be clean water or for example gas, like air, which, being lighter than the suspension will strive towards the center of the separator, carrying lighter material with it.
• An outlet 22 for heavy reject is installed at the chamber 34.
• At said heavy fraction chamber 34 preferably close to its inlet end there is arranged an inlet 32' for dilution/washing medium.
• the slot 36 is preferably adjustable for controlling the flow of the lighter subfraction separating from chamber 34 to the sorting channel.
• the slot 36 can be adjusted by moving the rotor 24 in relation to the housing 12, by means of levers or other suitable means ⁇ not shown) .
• the housing 12 of the separator 10 is not evenly cylindrical, but has expansions 38 at which the channel 28 for the heavy frac ⁇ tion is more spacious.
• the expansions 38 are preferably arranged in connec ⁇ tion with the fluid inlets 32.
• the section of housing 12 is correspondingly restrained after the expanded zone 38 so, that a throttling of heavy fraction channel 28 results. By the throttling of the heavy fraction channel 28 a better guiding into the sorting channel 25 of the lighter subfraction, separating from the heavy fraction is effectuated.
• the housing 12 of the separator 10 is static, which is preferred in view of the technical execution of the apparatus.
• the housing can, however, be made rotating without disturbing the essential func ⁇ tion of the process according to the invention.
• a tube 40 which forms a channel 42 for . the light fraction and/or gases.
• the central tube 40 rotates together with the rotor 24 and in the presented embodiment functions as a shaft for the rotor 24.
• the rotor 24 is turned by a drive (not shown), installed at the upper or lower end or both of the rotor.
• the rotor may be free wheeling without mechanical drive.
• the kinetic energy of the suspension fed into the inlet end and/or extrac ⁇ ted at the outlet end is transformed into rotating energy by means of a turbine effect, which turns the rotor in order to reach a separation effect.
• the rotor is connected to the central tube 40 by radial partitions 31 , which divide the sorting channel 25 into axial sorting chambers.
• radial partitions 31 which divide the sorting channel 25 into axial sorting chambers.
• slots or openings 37, 39 In the wall of tube 40 are slots or openings 37, 39, the edges of which are streamlined oblique for promoting the flow of suspension between the sorting channel 25 and the light fraction channel 42.
• the tube 40 can be throttled in the same manner as explained before regarding the heavy frac ⁇ tion channel for guiding the fractions into and out from the light fraction chan ⁇ nel 42.
• the light fraction channel 42 ends in a central light reject outlet 43.
• Said center piece 44 forms a continuation of the tube 40 and acts as a rotation shaft. Due to said center piece 44 an annu- lar channel 45 is formed at the inlet end of the separator.
• a first sorting of the suspension will take place in said annular channel between the housing 12 and the center piece 44. In this area the suspension is brought to rotate firstly by the tangential direction of the inlet 16 at the inlet end 14 and secondly by the vanes 46 attached to the center piece 44, shown in Fig 3.
• the rotor 24 reaches from the outlet end 18 of the separator toward the inlet end 14, ending however a certain distance from the inlet end, so that said annular channel 45 is formed.
• the function of the apparatus is independent of its measures or proportions, which can be varied according to the particular needs. Thus for suspensions of different types and of different consistency the preferred proportions may dif ⁇ fer from each other.
• the fibre suspension fed to the paper web forming is usually in the range of 0.2 to 2%. Because the amount of heavy reject in this connection is usually small, the space between housing 12 and rotor 24 is preferably only a fraction of the diameter of the very rotor.
• the inlet 16 of the separator 10 is shaped as a tangentially directed, narrowing pipe which enables the transformation of the energy of the suspension into rotation energy.
• the turbine effect thus reached may be sufficient for turning especially a light rotor, and no separate means for turning the rotor may be needed.
• Fig. 3 shows the said solid center piece 44, and the attached radial vanes 46. Close to the inlet, the vanes 46 are bent to form turbine blades so that as much rotation energy as possible is recovered from the fed suspension flow. Further off the inlet end the vanes straighten and accelerate the rotation of the suspension, helped by the driven shaft 44.
• the vanes 46 divide the sorting channel 25 into separate axial channels, in each of which the centrifugal force causes a separation of a lighter and a heavier fraction.
• Fig. 4 represents the section of the separator, where the first inlet 32 for dilu ⁇ tion/washing fluid joins the housing 12.
• the inlet 32 is arranged in an annular way, distributing the fluid evenly around the mantle of housing 12. After inlet 32, the mantle is somewhat expanded so, that the fluid can be caused to flow as laminarly as possible into the heavy fraction flowing past the inlet for washing out the lighter fibres from said heavy fraction.
• a fluid can be introduced into the separator 10 also earlier, for example close to the inlet end, forming a thin fluid layer at the surface of the mantle of hou ⁇ sing 12, so that the heavy fraction striving toward the mantle has to pass this fluid layer.
• the fluid can be fed into the separator tangentially or radially, lami ⁇ narly or turbulently, around the mantle or locally, depending on the effect desi ⁇ red by the fluid feeding at each point.
• Fig. 5 represents a section of the separator 10 at the sorting zone. It shows the mantle of housing 12, the rotor 24, the central tube 40 and the partitions 24, joining tube 40 and rotor 24 and reinforcing the construction.
• the parti ⁇ tions 31 divide the cannel 25 into separate channels, in which the sorting proceeds efficiently.
• Each of the separate channels formed in sorting channel 25 opens to the heavy fraction channel 28 as well as to the light fraction channel 42 through said slots or openings 26, 30, 37, 39.
• Fig. 6 represents the section of the separator 10 at the expanded section of outlet end 18.
• Wing-like means 33 reach from rotor 24 into the heavy fraction chamber 34, accelerating the heavy fraction, and improving the separation efficiency.
• the discharge pipe 22 for heavy fraction is arranged at the outer ⁇ most end of the chamber 34.
• the inner channel of central tube 40 may be throttled at this point in order to reduce the proportion of the lightest fraction. As seen in the Figure, it can also be somewhat expanded at its outer side for obtaining a desired suspension flow pattern.
• the partitions 31 should preferably be bent as turbine blades in order to recover the rotation energy as efficiently as possible.
• Fig. 7 represents the extension of sorting channel 25 at the outlet end 18, formed to an energy preserving outlet 20.
• the separator can be built without any channel for the light fraction, separating the suspension in two fractions only.
• the light fraction can also be brought to flow toward the inlet end of the separator as shown in Fig 8, representing one of many possible alternative embodiments of the invention.
• the heavy fraction channel 28 is relatively large and equipped with vanes for keeping the heavy fraction in rotation. No reject chamber 34 is needed.
• Fig. 8 represents an alternative embodiment of the present invention which like Fig. 1 has an inlet end 14 and an outlet end 18 and inlets and outlets 16, 20, 22 arranged at these.
• the rotor 24 reaches quite close to the inlet end 14 and the light fraction channel 50 is arranged in the inlet end of the separator 10, so that the light fraction is brought to accumulate close to the outer surface of a hollow tube 52 extending from the inlet end 14.
• the central tube 52 has a slot or opening 54, through which the light fraction can pass into tube 52.
• the light fraction is removed from the separator 10 through a channel 50 in the central tube 52, in the direction opposite to the suspension flow.
• the channel 50 has no other connection to the sorting channel 25 than said slot 54. It is, however possible to arrange multiple slots 37, 39 as mentioned in the description of Fig. 1 also in tube 52, which slots make possible the returning into sorting channel 25 of a relatively heavier subfraction from the light fraction channel 50.
• Fig. 8 there is a dilution liquid inlet 56 feeding fluid forming a liquid layer at the inner sur ace of housing 12.
• the central tube 52 and a connected solid central piece 58 function as a shaft of the rotor 24.
• the process according to the present invention comprises also processes, wherein the suspension is split into two fractions only, of which the outermost one is relatively heavier and the innermost one relatively lighter.
• the light fraction, the heavy fraction or the interme ⁇ diary fraction may be accept or reject in respect to the specific sorting process. It is essential for the process according to the invention that an integrated multiple stage sorting is provided in one continuous operation.
• the process yields a favorable sorting result partly because a dilution/washing medium is introduced into the suspension and partly because a lighter subfraction can transfer back into the intermediary fraction from the already separated heavy fraction.
• a heavier subfraction can transfer back from the already separated light fraction into the intermediary fraction and the separation of the heavy fraction and light fraction, respectively, continue throughout the length of the separator.
• the suspension to be sorted in the separator 1 0 according to Fig. 1 is a fibre suspension to be brought to the web forming part of a papermaking process.
• the suspension has been diluted to a consistency of 0.2 to 2 %, preferably about 0.5 to 1 .5 %.
• the suspension is fed into sepa ⁇ rator 10 through inlet 1 6 so that its kinetic energy is transformed into rotation energy in channel 45.
• the center piece 44 is turned so that vanes 46 cause the suspension to rotate with a rotation speed, sufficient for causing an effi ⁇ cient separation, preferably in the range of 300 to 1000 revolutions per minute.
• the axial speed of the suspension shall preferably be maintained at a minimum of about 3 meters per second.
• the centrifugal forces caused by the rotation of the suspension cause the suspension to separate according to specific weight, so that a heavy fraction strives toward the mantle of the housing 12 of separator 10, and a lighter frac ⁇ tion cumulates at the surface of center piece 44.
• an initial sorting of the suspension occurs in channel 45.
• the suspension flows forward in the separator, it encounters the rotor 24 rotating in the separator. A substantial part of the suspension is brought to flow inside the rotating rotor. Only the heavy fraction accumulated at the inner surface of the housing 12 remains still outside the rotor.
• the rotor 24 forms a main sorting channel 25, in which the separation of a heavier and a lighter fraction continues so, that the heavier fraction strives toward the mantle of rotor 24.
• the heavy fraction accumulated at the surface of housing usually contains a considerable proportion of acceptable fibres.
• washing liquid is fed into this fraction through the inlet 32 discharging annularly at the inner surface of the housing 12.
• the washing liquid is fed around the mantle as a laminar flow, and especially whereas the diameter of housing 12 preferably simultaneously expands, the washing liquid forms a relatively laminar flow along the inner surface of the housing, through which the heavy material fraction transfers, striving toward the mantle.
• lighter subfraction following the heavy frac ⁇ tion is released and suspended into the washing liquid.
• the flow should, however, constantly remain essentially laminar.
• the subfraction released from the heavy fraction follow the washing water through the slots 30 in the rotor 24 from the heavy fraction channel 28 into sorting channel 25.
• the flow from channel 28 into channel 25 can be promo ⁇ ted by throttling the suspension flow in the heavy fraction channel 28.
• the feeding of a diluting washing liquid into the heavy fraction cumulating at the inner surface of housing 12 is preferably repeated along the length of separa ⁇ tor 10 so that an integrated multistage washing of the heavy fraction is obtai ⁇ ned.
• backwater obtained from a forming process is used as the washing liquid.
• the suspension is separated into three fractions during the same sorting action, whereby the light fraction accumulated at the central piece 44 together with any contained gas is conducted into the light fraction channel 42 in the center of rotor 24.
• the central tube 40 forming the light fraction channel 42 are slots 39 similar to the ones of rotor 24, which permit the heavier subfraction separating from the light fraction to flow back into the sorting channel 25, from which channel correspondingly the separa ⁇ ting lighter subfraction can transfer into the channel 42.
• the slots 39 have an obliquely streamlined shape promoting the desired flow.
• the sorting will occur continually and manifold so that at the end of the separator very efficiently sorted suspensions are obtained.
• the heavy reject is further concentrated in a reject cham ⁇ ber 34, where the reject is extracted through heavy fraction outlet 22 at the outermost end of said chamber, whereas acceptable fibres separated from the reject in the reject chamber as a lighter subfraction are brought into the inter ⁇ mediate fraction constituting the accept through a slot 36 between rotor 24 and housing 12.
• the width of said slot 36 can be adjusted, affecting the flow of suspension flowing from the reject chamber into the accept and thus also the flow of heavy reject. For a certain suspension consistency and type optimum sorting conditions can thus be sought by controlling the suspension flow, the washing fluid flow and the width of slot 36.
• the intermediate accept fraction is fed into a tangentially narrowing outlet 18 so, that the rotation energy is recovered as pressure in the accept outlet and as rotation energy through the vanes shaped as turbine blades at the outlet 20.
• the heavy reject cumulating outside rotor 24 is extracted through outlet 22 and the light reject cumulating in the center of rotor 24 is removed through the light reject outlet 43.
• the centrifugal separator according to the invention functioning in one stage is particularly preferred for being used in the short circulation of the web for ⁇ ming of a papermaking process for obtaining a fast and controlled function and for avoiding the multiple feedback loops of centrifugal cleaners according to prior art.
• Fig. 9 represents the use of the separator according to the present invention in connection with a papermaking process disclosed in copending Patent Application FI 922285 by the present inventor.
• a separator according to the present inven ⁇ tion provides essential improvement also in a traditional papermaking process. When backwater recycling is accelerated and simplified the time needed for grade changes is reduced and process control is improved.
• Figure 9 represents a forming process for a paper web, where the advantages of a separator according to the invention, functioning efficiently in one single stage are utilized particularly efficiently.
• the paper stock is fed as a controlled flow at about 3 to 5% or higher consistency from stock preparation 124 to the short circulation.
• the stock is first diluted to a consistency of about 0.5 to 1.5%, whereafter it is brought to a separator 10 according to the present invention, which functions in a single stage, without recycling of reject.
• a separator 10 which functions in a single stage, without recycling of reject.
• backwater recycled free of air from the forming part is used for dilution and washing of reject.
• the cleaned stock is then brought forward to a screen 121 , preferably of a type disclosed by the present inventor in copending Patent Application FI 922284. Said screen functions in one single stage and also uses recycled air free backwater as dilution water.
• the stock is brought to the paper machine head- box 100.
• the stock is fed to a sheet forming part, which can be of different known types.
• sheet forming the major part of the water contained in the fibre suspension is drained into separate draining boxes 101 , 102, 103 in connection with the forming wire or wires.
• the back ⁇ water, collected in the draining boxes is recycled back into the main process flow, as separate flows, without passing through open tanks by means of multiple pumps, of which at least a part are preferably air separating pumps 1 10, such as gas separation pumps to copending Patent Application FI 922283 by same inventor.
• the backwater to be recycled is brought to the various dilution points of the short circulation as separate flows, so that the dilution water required by the separator according to the present invention, and by the screen following the same in the stock flow, flows directly to the stock main flow, without tube ramifications or upstream recircu ⁇ lating.
• the single stage function of the separator according to the present invention without feed back of reject and without recycling of backwater or fibre suspen ⁇ sion essentially accelerates reaching of a new state of equilibrium in connec ⁇ tion with a change of paper grade or process adjustment, and thus considerab ⁇ ly reduces the amount of waste paper produced at a grade change and impro ⁇ ves the process controllability.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Separation Of Solids By Using Liquids Or Pneumatic Power (AREA)
• Paper (AREA)
• Centrifugal Separators (AREA)

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• 1992
  • 1992-05-19 FI FI922282A patent/FI90358C/fi active
• 1993
  • 1993-05-19 AU AU40711/93A patent/AU4071193A/en not_active Abandoned
  • 1993-05-19 JP JP5519922A patent/JPH08500636A/ja active Pending
  • 1993-05-19 WO PCT/FI1993/000211 patent/WO1993023610A1/en not_active Application Discontinuation
  • 1993-05-19 EP EP93910040A patent/EP0643785A1/de not_active Withdrawn

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