Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
• • 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

Definitions

• the present invention relates to a process for the preparation of cooking liquors having high sulphidity for the sulphate pulp industry starting from chemicals available in the pulp mill or make-up chemicals common in the pulp mill.
• the invention considers the important pulp mill balance between sodium and sulphur and is particularly advantageous in cooking with high sulphidity, particularly in so-called modified
• NaSH and NaOH are expressed in molar units. This means e.g. that an aqueous solution containing sodium hydrogen
• the sulphate pulp mills often operate whithin the sulphidity range of 25 to 40% (white liquor sulphidity).
• a major part of the sodium reacts with carbon dioxide when burning black liquor to form sodium carbonate.
• the mixture of sodium sulphide and sodium carbonate forms a melt at the bottom of the soda recovery unit and this melt is withdrawn and is reacted with water to form so-called green liquor.
• a typical green liquor has the composition
• Chemicals recovery according to the "sulphate process” results in that a relatively large amount of sulphur reaches the oxidative zone and is rejected from the soda recovery unit mainly as sodium sulphate (electrical filter ash) and sulphur dioxide. If the white liquor sulphidity exceeds 35% problems begin to arise i.a. by high emissions of sulphur dioxide from the soda recovery unit. Scrubbing with alkaline medium is therefore often used in order to eliminate or strongly reduce the sulphur dioxide emissions.
• the green liquor obtained is converted to white liquor according to the known causticizing process.
• the composition of a white liquor may vary from mill to mill but approximate concentration values are
• Na 2 S + H 2 O ⁇ NaOH + NaSH this means that the amount of sodium, bound as carbonate, often amounts to more than 20% of the sodium present as hydroxide.
• the kappa number is a measure of the lignin content and the viscosity is considered to be a measure of the strength of the cellulose fiber. It is of interest to be able to cook the pulp to as low kappa number as possible. This especially applies if it shall be bleached to high (90 ISO) brightness. For this purpose there is required bleaching with chlorine-containing bleaching
• the alkali concentration shall be as constant as possible during the course of the cooking.
• the hydrogen sulphide concentration shall be as high as possible, particularly in the beginning of the bulk delignification phase.
• the hydrogen sulphide concentration can be low at the end phase of the cooking.
• the concentrations of lignin released and sodium ions shall be as low as possible, particularly in the last stage of the cooking.
• the temperature shall be low. particularly in the beginning and at the end of the cooking.
• item 2 is of special interest with regard to the present invention. So far one has been allowed to content with the concentration of hydrogen sulphide ions provided by the 40% sulphidity in the white liquor.
• the invention relates to a process for preparing, under reducing conditions, cooking liquors having high sulphidity for sulphate pulp cooking wherein the black liquor formed in the cooking process is passed, after evaporation, completely or partly to a reactor operating at an increased temperature which is obtained by energy supply from an external heat source and/or release of energy from the black liquor, a melt essentially consisting of sodium sulphide being formed and withdrawn to be further processed to cooking liquor.
• the process of the invention is characterized in that in addition there are added to the reactor the whole or part of the sulphur- containing and/or sulphur- and sodium-containing materials present in the pulp mill, including sulphur-containing and/or sodium- and sulphur-containing make-up chemicals used for the total chemicals balance of the pulp mill, in such a way that the mole ratio of sodium to sulphur in the total mixture fed to the reactor is within the range from 1.5 to 4.
• a solution of the melt is fed directly to the
• additional energy in addition to the energy released from the black liquor in partial oxidation, can be supplied to the mixing zone of the reactor by a hot gas, the heat content and oxidation potential of which are adjusted to the reduction work required.
• the heat energy may e.g. be supplied by a gas heated by a plasma generator.
• the very hot gas or gas mixture can also be formed directly or indirectly with an oxy-fuel burner.
• gas or gas mixture use can be made of air, recirculating process gas, hydrogen gas, natural gas, carbon monoxide, etc.
• gas or gas mixture is obtained by combustion of e.g. acetylene or liquified petroleum gas with oxygen enriched air or pure oxygen gas.
• a preferred process according to the invention is that the hot gas is fed to the reactor close to the material fed which in turn must be finely divided which can be obtained by different kinds of atomization techniques known by the man skilled in the art.
• the design of the reactor must be sufficiently
• the reactor volume must ensure a certain minimum residence time.
• the reactor is preferrably a closed reaction vessel and the temperature in the reactor shall be at least the temperature at which the sodium sulphide is formed under otherwise prevailing conditions.
• the man skilled in the art may establish said temperature from case to case, e.g. by routine experiments.
• the temperature is preferrably not below 700oC.
• the pressure in the reactor is preferrably atmospheric pressure. However, the process may be effected at an increased pressure, e.g. in order to reduce the reactor volume.
• Swedish Patent SE 8501465-2 there is disclosed a process to relieve the soda recovery unit by means of plasma gasification of a partial stream of the black liquor. This makes its
• the mole ratio of sodium to sulphur in the total mixture fed to the reactor is below about 4 and is within the range from 1.5 to 4, preferrably from 2 to 3.
• This adjustment of the sodium to sulphur ratio is effected by means of sulphur- containing and/or sulphur- and sodium-containing materials present in the pulp mill, including sulphur-containing and/or sodium- and sulphur-containing make-up chemicals used for the total chemicals balance of the pulp mill.
• the make-up chemicals used in order to adjust the mole ratio of sodium to sulphur correctly may consist of sulphur, sulphur dioxide, sulphuric acid, sodium hydrogen sulphate, sodium
• elemental sulphur may be used or any other sulphur- containing chemical having a Na/S ratio being equal to or below about 4.
• Example 1 The invention is further illustrated by means of the following working examples.
• Example 1 The invention is further illustrated by means of the following working examples.
• the following material streams were fed continuously per hour to a reactor operating at atmospheric pressure. - 620 kg black liquor (65% dry substance content) containing 129 kg sodium (Na) and 35 kg sulphur (S) per ton of black liquor. - a residual acid mixture from chlorine dioxide production according to the Mathieson process containing 80 kg H 2 SO 4 and 62 kg Na 2 SO 4 - 800 kg Na 2 SO 4 in the form of electrical filter ash.
• the above material streams were mixed with an oxygen-containing gas and passed to a reaction room.
• the oxygen-containing gas was heated to about 750oC in a plasma generator.
• a major part of the energy content of the liquor may be released by partial oxidation whereby it is not necessary to preheat the oxygen-containing gas in a plasma generator.
• Example 2 One proceeded in exactly the same way as in Example 1 and obtained a melt phase which that was withdrawn from the system.
• the sulphur dioxide added had been generated by roasting according to the process for preparation of sulphide-free liquor disclosed in EP 87850238.4. From the melt prepared there was prepared a 4.0 molar solution with regard to sodium containing 1.75 moles of NaOH, 1.75 moles of NaSH and 0.25 moles of Na 2 CO 3 .

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Cited By (6)

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• 1989
  • 1989-11-23 SE SE8903953A patent/SE465039B/sv not_active IP Right Cessation
• 1990
  • 1990-11-21 DE DE69013159T patent/DE69013159T2/de not_active Expired - Fee Related
  • 1990-11-21 MX MX023395A patent/MX173408B/es unknown
  • 1990-11-21 WO PCT/SE1990/000751 patent/WO1991008337A1/en active IP Right Grant
  • 1990-11-21 MY MYPI90002045A patent/MY104532A/en unknown
  • 1990-11-21 CA CA002069107A patent/CA2069107C/en not_active Expired - Lifetime
  • 1990-11-21 AT AT90917424T patent/ATE112595T1/de not_active IP Right Cessation
  • 1990-11-21 JP JP3500321A patent/JP2815701B2/ja not_active Expired - Fee Related
  • 1990-11-21 ZA ZA909337A patent/ZA909337B/xx unknown
  • 1990-11-21 ES ES90917424T patent/ES2062569T3/es not_active Expired - Lifetime
  • 1990-11-21 BR BR909007837A patent/BR9007837A/pt not_active IP Right Cessation
  • 1990-11-21 EP EP90917424A patent/EP0502052B1/en not_active Expired - Lifetime
  • 1990-11-21 CN CN90109309A patent/CN1030003C/zh not_active Expired - Fee Related
  • 1990-11-21 AU AU68836/91A patent/AU662882B2/en not_active Ceased
  • 1990-11-21 RU SU905052326A patent/RU2067637C1/ru active
  • 1990-11-21 AR AR90318435A patent/AR243947A1/es active
• 1992
  • 1992-05-19 NO NO921962A patent/NO176109C/no unknown
  • 1992-05-20 FI FI922288A patent/FI103902B/fi active

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