Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
  • B01F27/27—Mixers with stator-rotor systems, e.g. with intermeshing teeth or cylinders or having orifices
  • B01F27/272—Mixers with stator-rotor systems, e.g. with intermeshing teeth or cylinders or having orifices with means for moving the materials to be mixed axially between the surfaces of the rotor and the stator, e.g. the stator rotor system formed by conical or cylindrical surfaces
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
  • B01F27/27—Mixers with stator-rotor systems, e.g. with intermeshing teeth or cylinders or having orifices
  • B01F27/272—Mixers with stator-rotor systems, e.g. with intermeshing teeth or cylinders or having orifices with means for moving the materials to be mixed axially between the surfaces of the rotor and the stator, e.g. the stator rotor system formed by conical or cylindrical surfaces
  • B01F27/2722—Mixers with stator-rotor systems, e.g. with intermeshing teeth or cylinders or having orifices with means for moving the materials to be mixed axially between the surfaces of the rotor and the stator, e.g. the stator rotor system formed by conical or cylindrical surfaces provided with ribs, ridges or grooves on one surface
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
  • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
  • B01F2025/91—Direction of flow or arrangement of feed and discharge openings
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
  • B01F2025/91—Direction of flow or arrangement of feed and discharge openings
  • B01F2025/911—Axial flow
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
  • B01F27/80—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis

Definitions

• the present invention relates to a method and an apparatus for mixing ozone-bearing gas into a pulp-suspension of a cellulosic fibre material, for example so-called MC-pulp (medium consistency pulp) with a pulp-consistency of 5-25%.
• MC-pulp medium consistency pulp
• Such a mixing procedure is carried out in order to bleach the pulp-suspension with one or more bleaching agents comprising ozone, supplied with a carrier-gas.
• the object of the present invention is to overcome the aforementioned problem by achieving a more effective mixing of an ozone-bearing gas into the pulp-suspension and, in a particularly advantageous embodiment of the invention, make use of and recirculate unconsumed ozone-gas and inert carrier-gas.
• the above object is achieved by providing a method and an apparatus for mixing ozone-bearing gas into a pulp-suspen ⁇ sion of a cellulosic fibre material, according to the appended claims 1 and 4 respectively.
• Fig. 1 shows a diagrammatic cross-sectional view of a first embodiment of an apparatus according to the invention, provided with an axial pulp-inlet,
• Fig. 2 shows a cross-section along the line A-A in Fig. 1, showing two tangential gas-inlets according to the invention
• FIG. 3 diagrammatically shows a cut-out part of the stator provided with slots
• Fig. 4 shows a cross-sectional view of the stator in Fig. 3,
• Fig. 5 shows a diagrammatic cross-sectional view of a second embodiment of an apparatus according to the invention provided with a radial pulp-inlet and gas-separator adjacent the outlet.
• Fig. 1 shows a first embodiment of an apparatus for mixing ozone-bearing gas into a pulp-suspension of a cellulosic fibre material according to the invention.
• the apparatus comprises a pulp-inlet 1 through which pressurized pulp- suspension is fed in the axial direction of the apparatus according to the arrow 2.
• a processing-section 4 follows, the length of which is indicated with the dimen ⁇ sion 4 in Fig. 1.
• the processing section 4 is further divided according to the invention into a pre-fluidization- zone 5 and a mixing-zone 6, which in the figure are indicated with corresponding dimensions.
• Two gas-inlets 8, 9 are further connected to the processing section 4.
• an outlet 10 is provided, through which ready-mixed gas-pulp mix flows out radially from the apparatus in the direction of the arrow 11.
• the processing-section 4 is generally built up around a stationary cylindrical stator 13 which defines the main outer boundaries of the apparatus, and a rotor 14 coaxial therewith, which in the shown embodiment is journalled at one end via a shaft 15 in the right end of the apparatus in Fig. 1, i.e. adjacent to the outlet 10.
• the stator 13 and possible also the rotor 14, may instead be conically shaped.
• the rotor is hereby driven by an electric motor, not shown in the figure, connected to said shaft 15.
• the end-gable 18 of the stator 13 is sealed against the shaft 15 by means of a packing box 19.
• the rotor 14 exhibits a smooth cylindrical surface starting shortly after the gas inlet 8, 9 and ending at the end of the mixing zone 6 adjacent to the outlet 10.
• the rotor 14 exhibits a conical section 21 with the apex facing the pulp inlet 1 and which at the base of the cone transforms into the smooth cylindrical section of the rotor 14.
• the conical section 21 is hereby situated mainly in the pre-fluidization zone 5 of the processing section 4.
• the conical section 21 of the rotor 14 is provided with fluidization means 22 in the shape of radially projecting wings, which in an advantageous embodiment are at least slightly spiral-formed around the axis of symmetry of the rotor 14.
• This spiral formation is, however, not shown in the figure, where instead four projecting wings are provided, having internal openings 24 and being placed at right angles relative to each other.
• the length of the pre-fluidization zone 5 in the axial direction of the stator 15 and the rotor 14 is preferably 0,3 to 3 times the rotor diameter, more prefer ⁇ ably 0,5 times the rotor diameter in order to achieve the best fluidization effect.
• the mixing zone 6 starts directly after said pre- fluidization zone 5 with two gas inlets 8, 9 tangentially connected through the periphery of the stator 13 as can clearly be seen in the cross-sectional view in fig. 2.
• the figure also shows that the two gas inlets 8, 9 are con ⁇ nected at opposing sides of the periphery of the stator 13 in such a way that the gas is introduced in the rotational direction of the rotor 14, said direction being indicated by the arrow 26.
• the two incoming gas-flows are indicated with the arrows 27 and 28 respectively.
• the gas may of course also be introduced through a single gas inlet, although the shown embodiment with two gas-inlets 8, 9 yields a more equal gas-distribution in the initial stage of mixing.
• the length of the mixing zone 6 in the axial direction of the stator 13 and rotor 14 may be within the range of 2-10 times the rotor diameter, but preferably exceeds 3 times the rotor diameter and more preferably exceed 4 times said rotor diameter
• the radial distance between the rotor 14 and the stator 13 is adapted in such a way that it only allows passage of very small/infinitesimal fibre- flocks. Said distance, not including the flow-affecting means described hereinbelow, has proven optimal in tests when the inner diameter of the stator 13 is 1,01-1,4 times larger than the rotor diameter, preferably 1,01-1,3 times, more preferably 1,01-1,02 times and most preferably 1,01- 1,1 larger than the rotor diameter.
• the absolute value of the distance between the stator 13 and the rotor 14 may vary within the range 2-50 mm.
• the annularly-shaped channel 30 is thus very narrow in relation to the overall dimen ⁇ sions of the mixer and extends without interruption from the gas inlets 8, 9 to the end of the processing-section 4 adjacent to the outlet 10.
• the stator 13 is provided with flow-affecting means 32 in the shape of several slots (or bars as described hereinbelow) along its surface which faces the channel 30, which slots are designed to enhance the turbulence effect and the flock-decomposition in the through-flowing gas-pulp mix.
• the rotor 14 may correspon ⁇ dingly be provided with flow-affecting means 32, which is however not the case in the shown embodiment.
• stator 13 is provided with flow-affecting means 32 and the rotor 14 is smooth or vice versa, as well as an embodiment where the stator 13 and the rotor 14 are both provided with flow-affecting means.
• Fig. 3 and 4 an enlarged, diagrammatic view is shown together with a cross-sectional view of the flow-affecting means 32 of the stator 13, said means having the form of slots orientated in the axial direction of the stator 13.
• the dimensions of the slots are hereby for example 30 x 5 x 1 mm (length x width x depth) , but the length may vary, depending on the application, from 10 to 100 mm, the width from 2 to 20 mm and the depth from 0,1 to 10 mm.
• the length is generally 0,05 to 0,2 times the diameter of the rotor 14 and the width is generally 0,2 to 0,5 times the length of said rotor 14.
• said flow- affecting means 32 consist of a plurality of projecting bars on those surfaces of the stator 13 and/or the rotor 14 which face the annularly-shaped channel 30.
• the bars like the depicted slots, are orientated in the axial direction of the stator 13/rotor 14, and their dimensions in a common application are approximately 30 x 5 x 5 mm (length x width x height) , but the length may vary, depending on the application, from 10 to 100 mm, the width from 2 to 20 mm and the height from 1 to 20 mm. Generally, the length is 0,05 to 0,2 times the diameter of the rotor 14 and the width is 0,2 to 0,5 times the length.
• a second embodiment of the invention is shown, where the rotor 14 is instead doubly journalled in the bearing-houses 34 and 35 via a through-going shaft 15.
• This embodiment differs from the one described previously in that the stator 13 is provided with a tangential pulp inlet 1 as well as a tangential pulp outlet 10, and that a gas separator 38 is situated adjacent to the outlet 10 for separation and removal of unconsumed ozone and inert carrier-gas from the outflowing pulp-flow.
• the gas sepa ⁇ rator 38 comprises radial degassing-fluidization-wings 40 mounted on the rotor 14 adjacent to the tangential outlet 10.
• the outflowing pulp is forced out through the outlet 10 by means of the centrifugal force, and the remaining gases, i.e. unconsumed ozone and inert carrier-gas, are led out through an evacuation-channel 42 extending along the shaft 15 of the rotor 14, which evacuation-channel 42 ends in a degassing housing 43 situated adjacent to the end-gable 18 of the stator 13.
• the degassing housing 43 is provided with an outgoing tangential conduit 45 for recirculation of said gases in the process.
• stator 13 is sealed against the shaft 15 by way of two packing-boxes 47, 48 adjacent to said bearing housings 34 and 35 respectively.
• This embodiment with its tangential pulp inlet 1 has proven to give a particularly fast fluidization in the pre- fluidization zone 5.
• pressurized pulp-suspension is pumped in through the pulp inlet 1 and passes the pre-fluidization zone 5 where it is accelerated into a fluidized state with the fluidization-means 32 of the rotor 14, whereupon the fluidized pulp-suspension flows on into the narrow annularly-shaped channel 30 between the stator 13 and the rotor 14 in the mixing zone 6.
• ozone-bearing gas is supplied to the fluidized pulp-suspension through the two tangential gas inlets 8 and 9, whereupon mixing takes place during passage through the rest of the mixing zone 6.
• the turbulence-effect and the flock-decomposi ⁇ tion are enhanced in the through-flowing gas-pulp mix by way of flow-affecting means 42 along those surfaces of the stator 13 and/or the rotor 14 which face the channel 30.
• the resulting pulp-mix flows out through the outlet 10 after completed mixing in the mixing-zone 6 of the processing- section 4. Any unconsumed ozone and inert carrier-gas thus follows the pulp-flow out through the outlet 10.
• unconsumed ozone and inert carrier-gas is separated in a gas-separator 38 and is then evacuated through an outgoing conduit 45 in order to then be recirculated in the process, which makes this embodiment particularly advantageous.
• the kinetic energy supplied through the drive shaft 15 is exclusively used for effective mixing and not simultaneously for axial feeding through the device, since the pulp-suspension is here fed axially through the device, for example by way of pumps provided upstream of the pulp inlet 10.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20391401

Family Applications (1)

Country Status (3)

Cited By (2)

Citations (1)

• 1993
  • 1993-10-13 SE SE9303352A patent/SE501895C2/sv not_active IP Right Cessation
• 1994
  • 1994-10-11 AU AU79526/94A patent/AU7952694A/en not_active Abandoned
  • 1994-10-11 WO PCT/SE1994/000955 patent/WO1995010351A1/en active Application Filing

Patent Citations (1)

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