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 cooking.
• Sodium sulphide and the closely related chemical sodium hydrogen sulphide are often interchangeable with each other and the application thereof often differs in order to meet different sulphidity demands.
• the aqueous phase sodium sulphide hydrolyzes completely or partly to sodium hydroxide and sodium hydrogen sulphide according to Na2S + H2O -> NaOH + NaSH (1)
• the concept sulphidity in the pulp industry is usually expressed as wherein NaSH and NaOH are expressed in molar units. This means e.g. that an aqueous solution containing sodium hydrogen sulphide and sodium hydroxide having a sulphidity of 40% contains 4 times more moles of sodium hydroxide than sodium hydrogen sulphide.
• the equilibrium (1) expresses a solution having a sulphidity of 100%.
• a typical green liquor has the composition Sodium carbonate 90-105 g/l Sodium sulphide 20-50 g/l Sodium hydroxide 15-25 g/l (all substances calculated as sodium hydroxide).
• the green liquor obtained is converted to white liquor according to the known causticizing process, see for example US-A-4098639
• the composition of a white liquor may vary from mill to mill but approximate concentration values are Sodium hydroxide, NaOH 80-120 g/l Sodium sulphide, Na2S 20-50 g/l Sodium carbonate, Na2CO3 10-30 g/l Sodium sulphate, Na2SO4 5-10 g/l (all substances calculated as sodium hydroxide).
• Na2S is estimated to be fully hydrolyzed according to Na2S + H2O -> 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.
• Modified cooking according to the present technique is based upon the following process conditions:
• 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 cooking liquor is added at two or several places.
• An extra high sulphidity in the cooking liquor added in the beginning of the cooking is of greatest use while the sulphidity in cooking liquors added in the final phase of the cooking may be low.
• 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.
• the sodium sulphide melt obtained in the process of the invention may be dissolved in water and further processed to cooking liquor in a way known per se .
• a solution of the melt is fed directly to the digester for optimum use of its high sulphidity in modified cooking.
• a solution of the melt is mixed with part of the white liquor prepared in the usual way.
• 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 large in order for the reaction to have time to take place, i.e. 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 700°C.
• 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.
• 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 sulphate, sodium sulphite, sodium hydrogen sulphite and sodium thiosulphate.
• elemental sulphur may be used or any other sulphur-containing chemical having a Na/S ratio being equal to or below about 4.
• 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 750°C 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-A-0258196. 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 Na2CO3.

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

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