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
  • D21C11/00—Regeneration of pulp liquors or effluent waste waters
  • D21C11/04—Regeneration of pulp liquors or effluent waste waters of alkali lye
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S159/00—Concentrating evaporators
  • Y10S159/08—Multieffect or multistage

Definitions

• the invention relates to a method of reducing the viscosity and of improving the evaporability of black liquor from a cellulose cook.
• the effective combustion value of the waste liquor is then higher than that of a wet liquor and the volume of the steam generated by the recovery boiler is respectively greater.
• Swedish patent specification no. SE 8400904 discloses a method of decreasing the viscosity of black liquor after the evaporator immediately before the revocery boiler by oxidizing the liquor wherein after liquor of a higher dry-solids content can be introduced into the boiler.
• the oxidation reaction which is achieved by mixing warm oxidizing gas (such as air) in the liquor raises the temperature of the liquor and makes it more fluent or flowable.
• the method requires quite a complex apparatus for distributing the oxidizing gas evenly in the Liquid. The method is primarily effected immediately before the recovery boiler where a rise in the temperature of the liquid is achieved and pumping facilitated. If the method is applied in the process before the final evaporation, the carbon dioxide and organic acids produced in the oxidizing reaction reduce the pH of the liquor which may result in condensation of the lignin and cause considerable depositions on the heat transfer surfaces.
• Finnish patent specification no. 66035 discloses a method of removing organic material containing a macro-molecular fraction from the effluent of a cellulose cook. According to this method the macro-molecular fraction is removed by ultra- filtering of precipitating. Precipitation is performed by oxidizing the effluent which significantly reduces the viscosity of the effluent.
• the ultrafiltering method by which the macro-molecular fraction is separated from the effluent, requires, however, sizable and expensive apparatus.
• a complex apparatus is required for the precipitation. Addition of chemicals in the precipitation phase affects the chemical balance of the whole system. In continuous operation, separation of the chemicals is problematic and cannot easily be controlled or changed.
• the object of the present invention is to eliminate or minimise the above disadvantages and to provide a method for decreacing the viscosity of black liquor before final evaporation without separation of the different fractions of the black liquor which would then have to be treated separately.
• the main characteristic feature of the method of the present invention is that the temperature of the black liquor is raised above the cooking temperature, preferably up to 170 - 190°C, in order to split the macro-molecular lignin fractions.
• the method according to the invention provides for a controlled .reduction of the viscosity of the whole black liquor amount
• the capacity of an existing evaporation plant can be improved or in a new evaporation plant, the heat surface of the con ⁇ centrator can be dimensioned smaller. Further, the final dry- solids content of the liquor can be increased without any substantial changes in the pressurization or the apparatus, which improves the heat economy of the combustion.
• the flow resistance decreases the pur ⁇ pability of the liquor improves and the power consumption of the pump decreases.
• the sulfidity is 35 % the macro-molecular fraction (M > 10000) 25,1 g/kg dry solids has decreased after a cooking time of 170 min; after 110 min the fraction was 32,1 g/kg dry solids.
• the sulfidity is 25 % the amount of the macro- molecular fraction has decreased with the time.
• the sulfidity is zero no splitting of molecules can be seen. Thus, in order to secure good results, oxidation has to be prevented to preserve the sulfur in the sulfide state.
• the viscosity can be decreased in the black liquor itself without addition of chemicals or separation either during the cooking or the evaporation process by simple pressure heating.
• the temperature can be raised also in a separate circulation loop connected to the cooking process in continuous cooking in particular.
• the most economical heating method is chosen, for instance, direct or indirect steam heating or electric heating.
• the figure indicates the effect of heat treatment on black liquor viscosity.
• Black liquor samples having a dry-solids content of 65 %, 70 %, 75 % and 80 % were treated at 190°C. Viscosity was measured before the treatment, after 1 min, 5 min and 60 min. For instance, after a treatment of 60 min, the viscosity of the liquor having a dry-solids content of 70 - 73 % had decreased to the same level as the viscosity of an untreated liquor having a dry-solids content of 65 % which is the level of normal combustion liquid.
• the effect of further heating of mill liquor on the viscosity of the liquor is indicated by the following measurement results. Also the effect of Na_S or NaOH addition has been considered.
• the material tested was black liquor from a Kamyr-digestion having a dry-solids content of 71 %.
• a treatment at 120 C decreases viscosity but not even nearly as efficiently as a treatment at 190 C.
• a heat treatment of only one minute at 190 C decreases the viscosity from 200 mPas to 78 mPas .
• Addition of Na S seems to have a slight de ⁇ creasing effect on the viscosity, addision of NaOH on the other hand no effect at all.
• the present invention thus provides a method for decreasing the viscosity in order to improve the evaporability and li ⁇ uor transfer.
• the invention can be modified within the scope of protection defined by the patent claims .

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Cited By (3)

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Citations (3)

Family Cites Families (20)

• 1985
  • 1985-11-29 FI FI854732A patent/FI75615C/fi not_active IP Right Cessation
• 1986
  • 1986-11-24 WO PCT/FI1986/000133 patent/WO1987003315A1/en not_active Ceased
  • 1986-11-24 BR BR8607216A patent/BR8607216A/pt not_active IP Right Cessation
  • 1986-11-24 JP JP61506274A patent/JPS63502674A/ja active Granted
  • 1986-11-27 CS CS868786A patent/CS273179B2/cs unknown
  • 1986-11-28 PL PL1986262650A patent/PL155015B1/pl unknown
  • 1986-11-28 FR FR868616691A patent/FR2593528B1/fr not_active Expired - Fee Related
  • 1986-11-28 PT PT83838A patent/PT83838B/pt not_active IP Right Cessation
  • 1986-11-28 CA CA000524062A patent/CA1288203C/en not_active Expired - Lifetime
• 1988
  • 1988-05-25 SE SE8801948A patent/SE466756B/sv not_active IP Right Cessation
  • 1988-05-27 SU SU884355885A patent/SU1720498A3/ru active
• 1989
  • 1989-02-17 US US07/312,424 patent/US4929307A/en not_active Expired - Lifetime

Patent Citations (3)

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