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
• • 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
  • D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
  • D21C9/06—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents in filters ; Washing of concentrated pulp, e.g. pulp mats, on filtering surfaces
• • 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
• • 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

Definitions

• This invention relates to the making of pulp for paper products and, more particularly to an improved method and apparatus for adding chemicals and/or adjusting temperature in a bleaching operation.
• the pulp may be exposed to an ozone bleaching step.
• Ozone bleaching has markedly different requirements from those of the oxygen bleaching process. For example, oxygen bleaching is most efficient at high temperatures (approximately 190 degrees F) and high pH (8-9), while ozone bleaching is most efficient at low pH and a generally low temperature (120 degrees to 140 degrees F).
• the pulp must be acidified and cooled, with the same concerns for economy and efficiency, after exiting the oxygen delignification stage.
• this is accomplished by a method for uniformly adjusting chemical content and/or temperature of a wood pulp slurry in a pulp bleaching system by introducing pulp into a liquid filled wash press which has provisions for displacement washing and for extraction of liquid from the pulp. Liquid is extracted from the pulp to form a pulp mat in a first chamber, and the pulp mat is conveyed into a second chamber. A heated or cooled chemical solution is introduced into the second chamber in an amount and at a concentration and temperature sufficient to perform displacement washing and to bring the pulp mat to a predetermined temperature and chemical content.
• Liquid is displaced from the pulp mat by extracting liquid introduced with the pulp while simultaneously replacing the liquid with liquid from the second chamber to an extent required to yield pulp at a desired temperature and a desired chemical content, after which, liquid extraction is continued in order to bring pulp consistency to a desired level for discharge from the washing press.
• Fig. 1 is a schematic diagram showing a washing press used to add chemicals, to increase consistency of the pulp, and/or to adjust temperature of the pulp at the end of a bleaching stage;
• Fig. 2 is another schematic diagram of the washing press as applied in another bleaching stage in a pulp making process.
• Fig. 1 shows a washing press in which the chemical content and temperature of a pulp slurry is uniformly adjusted while the consistency of the slurry is increased.
• This press and the method of its operation promote uniform mixing of the chemical added with the pulp slurry, uniformity of pulp temperature, and minimum waste of the chemical.
• Washing press 100 contains two identical rolls 62, mounted on shafts 62b, all within a tank 64.
• Tank 64 has an arcuately shaped nip wedge 63 to decrease volume of chamber II of tank 64 and to train pulp into the nip between rolls 62.
• the press further comprises two baffles 66, substantially separating chambers, I and II. Streams 10, 15, and 17 combine in mix chest 60 to form stream 70 and to enter tank 64 in the chamber I between rolls 62 and baffles 66. Streams 14 are also shown as entering tank 64 in the chambers II between baffles 66 and tank 64.
• the streams 10 enter mix chest 60 where the consistency is reduced by the addition of liquor from streams 15 and 17.
• Stream 15 contains a part of the effluent stream 11 from rolls 62.
• Stream 14 is a solution of chemical 16, like sodium hydroxide, mixed with wash liquor from stream 19.
• a portion of wash liquor 19 is preferably mixed with chemical 16 to produce a chemical solution stream 14 which is then supplied to tank 64.
• the chemical material which is supplied to chamber II of stream 14 is of a sufficient strength and amount to provide the output pulp 13 from washing press 100 with a sufficient amount of chemical to satisfy downstream bleaching operations.
• the downstream operation would be an oxygen stage. It is well known that, for oxygen to react with lignin, typically 1-4% by weight of caustic soda (sodium hydroxide) has to be added to the pulp.
• an approximately 4% consistency pulp stream is provided from chest 60 as feed stock to both sides of the tank 64 along with the chemical solution stream 14. Consistencies are used for illustrative purposes to indicate the desirability, at various process stages, of lesser or greater consistencies.
• Rolls 62 are counter- rotating and will produce an output pulp mat 13 having a consistency of approximately 28%, or greater - a high consistency pulp mat.
• tank 64 The functions within tank 64 take place under differential pressure with pressurized feed stock, stream 70 from chest 60 and stream 14 injected into tank 64, for liquid extraction and displacement washing of the feed pulp slurry. Liquid extraction is driven by pressurized slurry in chambers I and II losing liquor to the relatively low pressure within perforated rolls 62. Properly applied, pressure or vacuum will drive the operation with equal effectiveness. Bleaching systems of the prior art, have introduced the required chemicals, e.g., alkali materials for a subsequent oxygen delignification stage, either into mix chest 60, or into the high consistency output stream 13 of the extraction press.
• the required chemicals e.g., alkali materials for a subsequent oxygen delignification stage
• baffles 66 are mounted on pivot points 66a and have mechanical positioning devices 66b which establish a "no load” baffle position.
• a pulp mat forms on rolls 62 by liquor extraction through the porous roll surfaces.
• Compaction baffles 66 gently iron the pulp mat but, more importantly, separate mat formation chamber I from chemical and temperature adjusting solution contained in chamber II.
• chamber I The space between the periphery of roll 62 and baffle 66 defines chamber I, into which is directed a preferably pressurized stream 70 of pulp slurry.
• Chamber II is defined between baffle 66, tank 64, and the arcuately shaped nip wedge 63.
• a chemical containing input stream 14, pressurized as is stream 70, is introduced into chamber II and comes in contact with the pulp mat as the mat emerges from Chamber I (behind baffles 66).
• the chemical containing solution of Chamber II begins to displace liquor from the pulp mat, after the pulp mat passes the end of baffles 66, and continues to do so until the pulp mat enters the nip between rolls 62 and above nip wedge 63.
• the pulp slurry stream 70 is directed into the first chamber I which, at its throat, would typically have a width of, approximately 20 to 80 millimeters, while the distance between baffles 66 and rollers 62, at the juncture of chambers I and II, would be on the order of 6 millimeters.
• chamber I exhibits a continuously decreasing width as the pulp mat advances to the end of baffles 66.
• the chemical containing stream 14 is introduced into chamber II, which is separated from chamber I by the compaction baffles 66. The stream 14 enters chamber II, joins with the pulp mat as it emerges from chamber I, and displaces liquor from the pulp mat until the mat enters the nip between rolls 62 just above nip wedge 63.
• the mat is discharged in stream 13 at high consistency (approximately 28%), at the required temperature, and having the required chemical content uniformly distributed therein.
• Slurry stream 70 is fed into washing press 100 at a pressure between 3 psi and 15 psi. This pressure is generally uniform throughout the press, except in the washing chamber II, where it is usually higher, and continually drives the liquid extraction due to the pressure differential through the surfaces of rolls 62. As the pulp layers formed on rolls 62 approach the nip of rolls 62, the mechanical pressure on the pulp mat increases significantly due to the convergence of nip wedge 63 and rolls 62 and because the rolls 62 are urged against each other at very high pressure.
• the liquor forced by hydrostatic pressure through the perforations into the interior of the rolls is drained away to seal tank 11.
• the loss of chemical material in the present process and apparatus is significantly reduced because only a small part of the original pulp liquor has to be displaced by the chemical solution.
• the balance of the liquor has been removed prior to contact of the pulp mat with the chemical solution.
• the amount of chemical introduced into chamber II of wash press 100 is generally around 2.5% sodium hydroxide if the high consistency pulp discharge stream 13 is to be introduced into an oxygen reactor.
• the 28% consistency slurry from output stream 13 of the washing press enters an oxygen reactor 82.
• the pulp slurry effluent 86 from oxygen reactor 82 together with liquors flowing from lines 96 and 95, all of them feeding into mix chest 60 and from there into inlet box 88, create a 4% consistency pulp slurry which has to be acidified and cooled in preparation for ozone reactor 114.
• a washing press is shown at 90, and it will drain liquor through line 92 into seal tank 6.
• Ozone bleaching requires a lower temperature for reaction than does oxygen bleaching and requires an acidic pulp, as opposed to an alkali pulp.
• acid from a source not shown
• wash liquor from conduit 120, which may be fresh water or liquor from a succeeding stage and which is passed through a heat exchanger 98 for cooling as required.
• the combined flow from conduits 120 and 140 is provided, via conduit 102, to a washing press 90, identical in operation and structure to that which has been already described. This time washing press 90 produces a very high consistency pulp slurry at approximately 35-45% consistency.
• the chemical solution, in this case acidic, as before is provided in one chamber, while the slurry is provided in another chamber.
• the mat After a mat of pulp has been formed on the rolls in the first chamber, the mat is exposed to the chemical solution in the second chamber where the chemical solution displaces the liquor from the mat to adjust the pH and the temperature mat. After passing through the nip of the rolls the output slurry is conveyed to an ozone reactor 114.
• wash liquor enters the washing press 90 in such a manner that only that portion which is to be combined with the acid, passes through heat exchanger 98, while the majority of the flow bypasses the heat exchanger as well as the acidification step and goes directly to mix chest 60.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=25539384

Family Applications (1)

Country Status (7)

Families Citing this family (3)

Citations (1)

Family Cites Families (4)

• 1993
  • 1993-12-10 WO PCT/US1993/012125 patent/WO1994015016A1/fr not_active Application Discontinuation
  • 1993-12-10 BR BR9307672-0A patent/BR9307672A/pt not_active Application Discontinuation
  • 1993-12-10 EP EP94904438A patent/EP0674729A4/fr not_active Withdrawn
  • 1993-12-10 JP JP6515246A patent/JPH08504899A/ja active Pending
  • 1993-12-10 CA CA 2151812 patent/CA2151812A1/fr not_active Abandoned
• 1995
  • 1995-06-13 NO NO952335A patent/NO952335D0/no unknown
  • 1995-06-16 FI FI952999A patent/FI952999A0/fi unknown

Patent Citations (1)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events