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
  • D21C9/1026—Other features in bleaching processes
  • D21C9/1052—Controlling the process
• • 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

Definitions

• the present invention relates to a method concerning the oxygen gas de- gnification of hgnocellulose containing pulp material in two stages In two-stage oxygen gas bleaching processes, the deiignification occurs mainly in the first stage In the second stage, deiignification occurs mainly through alkali extraction and alkaline hydrolysis
• the temperature is increased in the second stage in order to improve extraction whilst, at the same time, lowering the pressure to beneath 5 bar No large quantities of oxygen gas are required for the reactions in the second stage
• the oxygen gas bleaching process has been carried out hitherto in two upstream reactors, which often requires the provision of a pump between the stages An additional mixer is required, to distribute residual gas and avoid channelisation
• the pulp is heated by supplying steam between the stages, at a relatively high pressure This means that intermediate pressure steam is required
• the present invention solves these problems by regulating the pressure and the pulp level in the first reactor in such a way that the pressure in the top of the reactor as well as the pulp level will be kept constant during the continuous bleaching process
• the present invention thus relates to a method for the oxygen gas deiignification of lignocellulose containing pulp material in two stages, where a regulation occurs in that in the first reactor the pressure in the top of the reactor as well as the level of pulp are both kept constant with the aid of two regulating valves A first regulating valve is placed in the top of the reactor and a second regulating valve is placed level with the lower action radius of the discharge scraper beneath the level of pulp in the upper part of the reactor
• the pulp is heat- ed with low-pressure steam
• gas is separated from a first upstream flow reactor under a pressure of 5-15 bar, preferably about 8 bar
• the gas is separated through a regulating valve, so that the largest possible amount of gas will be discharged at the prevailing pressure
• the dwell time in the first reactor is 10-60 mm and the temperature below 90°C
• the regulating valve 1 is controlled partly by the gas pressure in the reac- tor and partly by the pressure difference measured between two pressure sensors
• the pressure in the gas phase is registered by a first pressure sensor 3 placed in the top of the reactor
• a second pressure sensor 4 placed beneath the pulp level registers the pressure on the pressure sensor level The higher the pulp level, the greater the pressure difference
• the regulating valve 1 is throttled for gas at increasing pulp levels and is opened at decreasing pulp levels
• the regulating valve 2 is controlled by the pressure in the top of the first reactor, such as to maintain a high pressure level
• the valve 2 is placed on a level with the lower action radius of the discharge scraper beneath the level of pulp in the upper part of the reactor
• the cross-sectional area is greater there than at the top of the reactor, which enhances the departure of gas from the pulp surface
• the pulp is heated after the regulating valve 2
• the pressure drop over the regulating valve 2 enables that low pressure steam can be used instead of high- grade medium pressure steam for the heating of the pulp before the second reactor
• the pressure drop over the regulating valve 2 also results in a certain turbulent pulp flow so that the admixture of steam is more effective
• the pressure in the reactor 2 is between 0 and 3 bar, preferably atmospheric pressure, and the temperature is above 85°C
• the temperature difference between the reactor 1 and the reactor 2 is less than 20°C, preferably less than 15°C
• the average consistency of the pulp is between 8 and 20%

Landscapes

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

Applications Claiming Priority (3)

Publications (1)

Family

ID=20412917

Family Applications (1)

Country Status (5)

Families Citing this family (1)

Family Cites Families (4)

• 1998
  • 1998-10-08 SE SE9803474A patent/SE9803474L/ not_active Application Discontinuation
• 1999
  • 1999-10-04 BR BR9914337-2A patent/BR9914337A/pt not_active IP Right Cessation
  • 1999-10-04 WO PCT/SE1999/001761 patent/WO2000020678A1/en not_active Application Discontinuation
  • 1999-10-04 EP EP99956419A patent/EP1155183A1/de not_active Withdrawn
  • 1999-10-04 JP JP2000574767A patent/JP2002526684A/ja not_active Withdrawn

Non-Patent Citations (1)

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