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
  • 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
  • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
  • B01F27/50—Pipe mixers, i.e. mixers wherein the materials to be mixed flow continuously through pipes, e.g. column mixers

Definitions

• Figures 13-14 are isometric views showing details of construc- tion of the basket and screen of Figures 11-12.
• Figure 13 is with the screen and Figure 14 is without the screen.
• Figures 15-16 show a modification to the dewatering chamber of Figures 11-13.
• Figure 15 is a horizontal plan view partially in cross section and Figure 16 is a vertical cross section taken along line 16-16 of Figure 15.
• Figure 17 is a vertical cross section of a reactor showing an annular return line and a bottom dewatering chamber.
• Figure 18 is a horizontal cross section taken along line 18-18 of Figure 17.
• Figure 19 is a vertical cross section of a reactor showing an annular return line and a top dewatering chamber.
• Figure 20 is a vertical cross section of a reactor showing a central return line and a top dewatering chamber.
• Figure 21 is a horizontal cross section taken along line 22-22 of Figure 21.
• the reactor 10 has an outer shell 11, a cover 12 and base 13.
• a cental shaft 17 extends through these apertures.
• the shaft rotates on bearings, the number depending on the length of the shaft. Three bearings are shown: upper bearing 18, central bearing 19 and lower bearing
• the central bearing 19 is held in place by struts 21 extending between the outer shell 11 and the bearing.
• the shaft 17 is turned by motor assembly 22.
• Each of the chambers 14a-f has an impeller 23a-f attached to the shaft 17.
• the impeller may be of any appropriate design. A four bladed impeller is shown, but a six bladed impeller could normally be used. It mixes the pulp slurry with the ozone in the chamber.
• a series of baffles 24a-f are placed in each cell. The number and size of the baffles will depend on the size of the reactor. Four are shown in each cell.
• the lower chamber of the reactor is a dewatering chamber.
• the pulp slurry has been at a consistency in the range of 0.01 to about 0.7% during its treatment in the reactor. Liquid is removed from the pulp slurry, before it leaves the reactor so that the slurry will be at a consistency in the range of 0.5-4% as it leaves.
• the dewatering chamber 14g has a series of baffles 25 which are similar to the baffles 24 in the other chambers except that the baffles 25 have apertures 26 which allow the passage of filtrate around the exterior liquid section of the dewatering chamber.
• the baffles also act as supports for the screen 27 which is concentric with the shaft 17 and the outer wall 11.
• the screen 27 divides the dewatering chamber into the outer annular liquid chamber 28 and the inner slurry chamber 29.
• Impellers 30 are attached to the shaft 17.
• the outer edges of the impellers 30 have foils 31 which remove the fiber mat from the interior surface of the screen so the liquid may continue to pass through the screen at a high flow rate and continue to prevent pulp from accumulating in the dewatering chamber .
• the screen 27 acts differently from the usual pulp screen.
• the usual pulp screen has apertures or slots large enough to allow the pulp fibers to pass through the screen while retaining the larger knots, shives or fiber bundles within or on the screen.
• the purpose of the screen in the present dewatering chamber is to retain all of the fibers within the dewatering chamber while allowing the water to pass through.
• the preferred material of construction of the screen is stainless steel.
• the apertures should not be greater than the length of a pulp fiber being processed to prevent the pulp fibers from passing through them. This can be from 0.8 to 2 mm.
• the maximum mesh size would be 30.
• the mesh size normally would be 60. In operation the pulp slurry enters through the upper pulp slurry inlet pipe 32 and passes down through the chambers 14a-f.
• each of these chambers the slurry is mixed with ozone by the impellers 23a-f.
• the ozone is normally admitted beneath the bottom impeller through pipe 38 at the bottom of the reactor and passes upwardly through the chambers and leaves the pulp slurry at the upper surface of the slurry in chamber 14a.
• the filtrate recirculation pipe 36 has an inner diameter that is 7.7 to 45% of the inner diameter of the reactor. Normally the inner diameter of the recirculation pipe would be no more than 24% of the inner diameter of the reactor. Other recirculation passages may be used in place of this exterior pipe. These will be described later. They may have different cross sections or different locations. In each instance the inner cross-sectional area would be equal to a circular cross section having an inner diameter of 7.7 to 45% of the inner diameter of the reactor. The preferred sizes would also be the same.
• a preferred inner diameter of the recirculation pipe when the flow is downwardly from the upper dewatering chamber is 20 to 30% of the inner diameter of the reactor.
• Figures 7 and 8 show another modification of the dewatering chamber.
• the outer annular chamber 39 is the slurry chamber and an inner annular chamber 40 is the filtrate chamber. Because the passage of filtrate is from the outer annular chamber 39 to the inner annular chamber 40, the foils 41 are on the outside of the screen 27". There is less chance of damage to the screen by the impeller.
• the foils 41 remove the pulp mat from the screen 27".
• the foils 41 are the inner edges of impeller arms 42 of the dewatering chamber impeller assembly 43.
• the impeller arms 42 are attached to the central shaft 17" by impeller elements 44.
• Figures 9 and 10 show other configurations of screens and impellers in the dewatering chamber.
• the screen 27'" in Figure 9 is convex toward the center.
• the screen 27"" in Figure 10 is accordian shaped to provide greater surface area.
• the outer bars 53 fit into the outer shoulders 60 and 64 and are fixed to the rings 51 and 52.
• the inner bars 54 fit into the inner shoulders
• the pressure of the fiber and slurry against the screen 27"'" may cause the screen to tear along ⁇ the outer bars 53. Several actions may be taken to prevent this. The corners of the outer bars next to the screen 27'"" may be beveled to remove any cutting edge.
• An apertured backing plate 56 may also be provided. These plates are on the outflow side of the screen 27'"", support the screen, extend between the outer bars 53, and fit into and are fastened to the outer shoulders 60 and 64 of the rings 51 and 52.
• Each of the backing plates 56 have apertures 65 through which the liquid passes.
• the size and number of the apertures will depend upon the pressure of the slurry against the screen.
• the plate which is concave to match the contour of the rings and screen, must support the screen and prevent its tearing. If the pressure is not great, then the backing plate may be omitted.
• the slurry within the cylinder formed by the screen 27'"" is kept in turbulence adjacent the screen by the foils 66 which rotate within the inner circumference of the cylinder formed by the inner faces of the inner bars 54.
• the turbulence of the slurry created by the foils keeps the fibers from clogging the screen 27'"".
• the foils 66 are attached to the central shaft 17'"" by upper and lower arms 67 and 68.
• the number of foils will depend upon the size of the basket, and the types and concentration of the slurry. Four foils are shown. The speed of these foils will also determine the maximum pressure drop across the screen at which the screen can be operated.
• OMPI ⁇ higher the speed, the greater the pressure drop.
• high motor speeds also increase the tendency of the screen to tear.
• Another action that may be taken to prevent tearing of the screen is the choice of a slower rotor speed. In one experiment, a screen having an exposed area of 1.7 ft.
• Figures 15 and 16 show the preferred basket screen housing used when the flow of slurry is inward rather than outward.
• the differences between this construction and that shown in Figures 11-14 are that the outer bars 53' are movable, the inner bars 54' are fixed, the fasteners 55' attach the outer bars to the inner bars, the apertured plates 56' are on the inside of the screen 27""" and the foils 66' are on the outside of the screen and are held by the upper arms 68' only.
• the other reference numerals, the construction and the operation are the same as in Figure 7.
• Figure 19 illustrates the annular return line used in co-current flow.
• the reactor 10"""” has the same flow pattern as reactor 10' in Figure 6.
• the filtrate enters the annular passage 69' through aperture 71', travels down the passage 69' and through apertures 72 into lower chamber 14f"""".
• the rest of the apparatus, the reference numerals and the operation are the same as in Figure 6.
• the dewatering device 74 is mounted on the shaft 73 by upper and lower plates 78 and 79, and rotates with the shaft.
• the screen 75 may be mounted on the plates 78 and 79 in any convenient manner.
• a construction similar to that shown in Figures 15 and 16 is preferred. In that construction, upper wall 46' would be the equivalent of upper plate 78, inner wall 45' the equivalent of shaft 73, and divider plate 15a""" the equivalent of lower plate 79.
• the foils 80 are on the ends of baffles 24a"""".
• the inner cross-sectional size of the return line would be equal to a circular cross section having an inner diameter of 7.7 to 45% of the inner diamter of the reactor. This dimension will be called “equivalent diameter" for all cross sections and types of return lines or pipes.
• the normal equivalent inner diameter is 7.7 to 24% of the inner diameter of the reactor, and the equivalent inner diameter of the downflow line would be 20 to 30% of the inner diameter of the reactor.

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

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• 1984
  • 1984-06-14 FI FI850580A patent/FI850580A7/fi not_active Application Discontinuation
  • 1984-06-14 WO PCT/US1984/000905 patent/WO1985000046A1/fr not_active Ceased
  • 1984-06-14 AU AU30682/84A patent/AU3068284A/en not_active Abandoned
  • 1984-06-14 JP JP59502445A patent/JPS60501565A/ja active Pending
  • 1984-06-14 EP EP19840902488 patent/EP0148220A4/fr not_active Withdrawn
• 1985
  • 1985-02-11 NO NO850509A patent/NO850509L/no unknown

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