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EP0047656A1 - Procédé et appareil pour la délignification à l'oxygène de pâte - Google Patents

Procédé et appareil pour la délignification à l'oxygène de pâte Download PDF

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Publication number
EP0047656A1
EP0047656A1 EP81304078A EP81304078A EP0047656A1 EP 0047656 A1 EP0047656 A1 EP 0047656A1 EP 81304078 A EP81304078 A EP 81304078A EP 81304078 A EP81304078 A EP 81304078A EP 0047656 A1 EP0047656 A1 EP 0047656A1
Authority
EP
European Patent Office
Prior art keywords
pulp
reaction zone
oxygen
consistency
delignification
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP81304078A
Other languages
German (de)
English (en)
Inventor
Edward F. Elton
Vincent L. Magnotta
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Air Products and Chemicals Inc
Black Clawson Co
Original Assignee
Air Products and Chemicals Inc
Black Clawson Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Air Products and Chemicals Inc, Black Clawson Co filed Critical Air Products and Chemicals Inc
Publication of EP0047656A1 publication Critical patent/EP0047656A1/fr
Ceased legal-status Critical Current

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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
    • D21C9/1068—Bleaching ; Apparatus therefor with O2

Definitions

  • This invention relates to a process and apparatus for the oxygen delignification of fibrous materials, and more particularly to the medium consistency oxygen delignification of bleachable grade pulp and other fibrous materials using a series of tubular reaction zones.
  • medium consistency pulp at a consistency of from 8 to 20% along with alkaline materials are introduced into a substantially horizontal reaction zone.
  • Oxygen is added to delignify the pulp while the mixture of oxygen, pulp, and alkaline materials is agitated and transported through the reaction zone.
  • Apparatus for delignifying the pulp includes a tubular reaction zone, means for introducing oxygen gas and alkaline materials into the reaction zone, pump means for introducing pulp into the reaction zone, and means to transport and agitate the mixture of pulp, oxygen, and alkaline materials through the reaction zone.
  • the present invention provides a medium consistency process and apparatus utilizing one or more substantially horizontal agitated tubular reaction zones which produce rapid oxygen delignification rates at low alkali charges, minimize oxygen requirements, and yield pulps having high viscosities.
  • the use of rotary screws or paddles in the one or more reaction zones provides the agitation required to enable good mixing of oxygen with the medium consistency pulp and alkaline chemicals as well as controlling the pulp retention time in each reaction zone.
  • intermediate consistency it is meant that the consistency of the pulp supplied to and maintained in the reaction zone is from 8-20% and preferably 10-15%. This is to be distinguished from prior high (above 20% and preferably 25-30%) and low (less than 8% and preferably 1-5%) consistency delignification systems.
  • the oxygen delignification system of the present invention can be used to delignify any type of pulp including mechanical pulps, thermomechanical pulps, semichemical or modified mechanical pulps, chemical pulps, and secondary fiber. Additionally, straw, flax, and bagasse can also be delignified as well as pulp mill screen rejects and knots.
  • the starting materials for the process are unbleached wood pulps such as softwood kraft pulps having Kappa numbers between 20 and 50 or hardwood kraft pulps having Kappa numbers between 10 and 30, high yield pulps (i.e., 55-60% yield) cooked to near the point of fiber liberation such as softwood kraft pulps having Kappa numbers between 50 and 80 or hardwood kraft pulps having Kappa numbers between 25 and 50, or fiberized pulp mill screen rejects and knots.
  • unbleached wood pulps such as softwood kraft pulps having Kappa numbers between 20 and 50 or hardwood kraft pulps having Kappa numbers between 10 and 30, high yield pulps (i.e., 55-60% yield) cooked to near the point of fiber liberation such as softwood kraft pulps having Kappa numbers between 50 and 80 or hardwood kraft pulps having Kappa numbers between 25 and 50, or fiberized pulp mill screen rejects and knots.
  • the pulp or other fibrous material may be sent directly from the blow tank of a chip or raw material digester or cooker to brown stock washers which are typically operated in the medium consistency range.
  • the pulp may, optionally, be sent to a further refining stage before or after leaving the brown stock washers.
  • the screen rejects and/or knots removed from the pulp stream may be fiberized in a further refining stage and then recombined with the main pulp stream for the oxygen delignification process.
  • the pulp is then introduced, at a medium consistency of between 8 and 20%, and preferably 10-15%, into a substantially horizontal tubular reaction vessel where it is contacted with oxygen gas and alkaline chemicals.
  • a thick stock pump is used to feed the pulp into the reaction vessel. Use of the thick stock pump prevents the loss of gas pressure from the vessel and does not severely compact the pulp so that uniform oxygenation and delignification can occur.
  • Oxygen may be introduced into the delignification system either at one injection point or multiple injection points. Typically, oxygen gas will be injected on the lower side of the reaction vessel. Partially spent gas may, optionally, be removed from the delignification system by venting to the atmosphere or it may be collected for recycle. Additionally, the partially spent gas may be drawn off and utilized for lime kiln enrichment, waste water treatment, or other suitable uses. Any organic compounds or carbon monoxide formed during the delignification reaction may be removed by passing the gas through a catalyst bed before reuse.
  • Alkaline pulping chemicals are also introduced into the reaction vessel to aid in the delignification.
  • alkaline chemicals which are suitable for use in the practice of the present invention include sodium hydroxide, sodium carbonate, sodium borate compounds, ammonia, oxidized kraft white liquor, and mixtures thereof.
  • at least a portion of the total charge of alkaline chemicals is added to the pulp prior to its passage through the thick stock feed pump into the first reaction zone. This insures that the pulp has an alkaline pH when the pulp enters the first reaction zone and also lubricates the pulp for easier pumping.
  • An additional portion of the total charge is added to the first reaction zone from one . or more injection points along the top of the vessel.
  • Magnesium sulfate or other known protector chemicals or catalysts for preserving the viscosity and strength of the pulp may be introduced into the pulp either before or after the thick stock feed pump.
  • Steam is also added to the pulp prior to its entry into the thick stock feed pump.
  • the steam aids in expelling excess air from the pulp prior to delignification. Additional steam may be injected into the reaction vessel as needed in order to maintain the desired reaction temperature, although the exothermic delignification reaction supplies a substantial fraction of the heat requirement.
  • a rotary screw or series of paddles agitates the pulp, oxygen, and alkaline chemical mixture. It has been found that a solid flight helical screw extending the entire length of the reaction zone produces the gentle agitation necessary for uniform and rapid delignification. Satisfactory delignification is achieved by rotating the screw at a speed of less than about 15 rpm and preferably 1-6 rpm. In another embodiment of the invention, one or more additional substantially horizontal tubular reaction vessels are utilized to achieve an additional amount of delignification of the pulp.
  • reaction temperature alkali charge, type of alkaline chemical, oxygen partial pressure, and retention time depend on the type of material being treated and the desired degree of delignification. Typically, temperatures may range from 80 0 to 160°C, alkaline chemical charges from 1 to 20% calculated as Na 20 on oven dry material, and oxygen partial pressures from 2.1 to 14.1 K g/cm 2 (30 to 200 psi). Appropriate retention times have been found to be 5 to 120 minutes.
  • pulp at from 8-20% consistency and preferably 10-15% consistency from the brown stock washers is introduced into a first horizontal reaction vessel or tube 10 by a thick stock pump 12.
  • Inclined reaction tubes may also be employed, but the angle of incline should not exceed approximately 45 degrees to avoid compression and dewatering of the pulp in the lower end of the tube, which will interfere with uniform mixing of oxygen.
  • the reaction vessel is illustrated as a cylindrical reactor tube, noncylindrical tubes such as a twin-screw system may be utilized.
  • Pump 12 may be a Moyno progressing cavity pump available from Robbins & Myers, Inc., Springfield, Ohio.
  • pump 12 may be a Cloverotor pump available from the Impco Division of Ingersoll-Rand Co., Nashua, New Hampshire, or a thick stock pump manufactured by Warren Pumps, Inc., Warren, Massachusetts.
  • steam Prior to introducing the pulp into thick stock pump 12, steam may be injected into the pulp via line 14.
  • the steam aids in expelling excess air from the pulp and also raises the temperature of the pulp somewhat.
  • This addition of alkaline material can be made through line 16.
  • the alkaline material serves to lubricate the pulp for easier pumping as well as to insure that the pulp will have an alkaline pH when it enters reaction tube 10. Alternatively, all of the charge may be added at this point.
  • the total alkaline material charge will amount to from 1 to 20% by weight calculated as Na 20 of the oven dry weight of the raw fibrous material.
  • alkaline materials suitable for use in this invention include sodium hydroxide, sodium carbonate, sodium borate compounds, ammonia, oxidized kraft white liquor, and mixtures thereof although other known alkaline pulping liquors may also be used.
  • oxygen gas is introduced into reaction tube 10 through line 18.
  • oxygen may be introduced at a number of points along the length of tube 10.
  • the oxygen partial pressure maintained in the system is from about 2.1 to 14.1 Kg/cm 2 (30 to 200 psig).
  • Spent gas may be removed from the system by venting it to the atmosphere. Alternatively, it may be recovered for recycle to the reaction tubes or may be used for other purposes such as lime kiln enrichment or waste water treatment. Any organic vapors or carbon monoxide produced during the delignification reaction can be removed by passing the gas through a catalyst bed.
  • the delignification reaction is carried out by mixing the pulp, oxygen, and alkaline liquor which is injected through line 20 and sprayed over the pulp along the length of the tube.
  • alkaline liquor gradually along the length of the tube rather than all at once as is conventional in high consistency (i.e., 20-30% consistency) oxygen delignification, better pulp viscosity and strength is achieved.
  • Another advantage to gradually adding the alkaline liquor is that the exothermic delignification reaction is more easily controlled and the risk of localized overheating is diminished.
  • Satisfactory gentle agitation can be achieved by rotating screw 22 with drive means 23 at a rate of less than about 15 rpm and preferably 1-6 rpm.
  • the system is operated so that a gas space remains at the top of reaction vessel 10 and the vessel is less than full of pulp.
  • Total retention times of the pulp in the system may vary depending upon the nature and condition of the pulp and the desired amount of delignification to be accomplished. Retention times of between 5 and 120 minutes have been found to be satisfactory.
  • Steam may be injected into the reaction vessel through line 46 to maintain the temperature within the preferred 80 0- 160 o C range.
  • the pulp Upon completion of the delignification reaction, the pulp exits vessel 10 through outlet 26 and is passed to blow tank 28. The pulp is then discharged using a conventional blow wiper discharger.
  • pulp from washer 50 is sent through refiner 52 for further fiberization before being fed to thick stock pump 12. Since the consistency of the pulp leaving washer 50 will be in the medium consistency range, the pulp can be refined and then fed to the reaction vessel at the same consistency without any need for any dewatering.
  • Refiner 52 may be utilized in instances where delignification is to be carried out on pulp having an initially high Kappa number such as high yield softwood kraft pulp having an initial Kappa number greater than about 50.
  • Fig. 2a Also illustrated in Fig. 2a is the use of one or more subsequent substantially horizontal reaction vessels such as vessel 30 to carry out further delignification on the pulp.
  • pulp exiting one end of vessel 10 drops into vessel 30 where it is transported along the length of the vessel with gentle agitation by rotary screw 32 having solid helical flights 34 and driven by a suitable drive means 33.
  • Steam may be added through line 48 to maintain the temperature in vessel 30 within the preferred range of 80-160°C. Additional oxygen may be injected through line 18a if required.
  • Fig. 2b Yet another embodiment of the invention is illustrated in Fig. 2b in which like components are represented by like reference numerals.
  • pulp is transported from an initial cooking or digestion stage through line 54 to screens 56 where oversize slivers, shives, knots, and other impurities are removed.
  • the accepted pulp passes through line 58 into pulp washer 50 while the rejected material is sent to refiner 52 for further fiberization before being recombined with the main pulp stream through line 60.
  • This combined pulp stream is then washed and oxygen delignified as described above to yield a bleachable grade pulp.
  • a northeastern softwood kraft pulp having an initial Kappa number of 29.3 and a viscosity of 26.9 centipoise (cps) was oxygen delignified in accordance with the process of the invention.
  • the reaction conditions were 10% pulp consistency, 7 Kg/cm 2 (100 psig) total gas pressure, and a 3% sodium hydroxide dosage by weight based on dry pulp.
  • Retention time in the reaction zone was varied from 8 to 16 to 39 minutes by varying the speed of the rotary screw in the reactor.
  • the pulp feed rate was set at either 1542 Kg/day or 4536 Kg/day (1.7 ton/day (T/D) or 5.0 T/D).
  • Fig. 3 That graph shows a linear relationship between pulp viscosity and Kappa number at up to 60% delignification, where This result is surprising because high pulp viscosities, which are indicative of high pulp strength, were obtained at a relatively high percentage of delignification.
  • Commercial high consistency oxygen delignification systems are limited to about 50% delignification due to severe losses in pulp strength (measured as greatly lowered pulp viscosities) beyond that point.
  • Softwood kraft pulp having an initial Kappa number of 29.5 was oxygen delignified in a 2 liter autoclave at 110°C and an oxygen gas pressure of 10.5 Kg/cm 2 (150 psig) for a time sufficient to achieve a final Kappa number of 18.5.
  • Several tests were run with the consistency of the pulp varied from 2% to 15% to 28%. The results are reported in Table I below.
  • a high yield softwood kraft pulp near the point of fiber liberation and having an initial Kappa number of 59.4 was oxygen delignified in an autoclave at temperatures ranging from 100-130 o C and at a total gas pressure of 8.4 Kg/cm 2 (120 psig).
  • the pulp was maintained at a medium consistency for an approximately 15 minute reaction time as the charge of alkaline (caustic) chemicals was varied from 2-6% by weight based on oven dry pulp.
  • the curve labeled A in which the pulp was continuously gently agitated in the autoclave shows a greater reduction in Kappa number (indicative of a greater delignification rate) than the curve labeled B in which no agitation was performed.
  • the results show the importance of gentle agitation of pulp when delignifying at medium consistency to improve the rate of delignification of the pulp.
  • Tests were made using a softwood kraft pulp having an initial Kappa number of 29.5 to determine the effect of pulp consistency on the extent of delignification for a given alkaline chemical (caustic) dosage and reaction time.
  • the tests were carried out in a 2 liter autoclave at 110 0 C and 10.5 Kg/cm 2 (150 psig) gas pressure for 20 minutes.
  • Low (2%) consistency tests were done under conditions of vigorous agitation (rotation of stirrer at 1250 rpm) while the medium (15%) and high (28%) consistency tests were conducted without agitation. The results are shown in Fig. 6.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)
  • External Artificial Organs (AREA)
EP81304078A 1980-09-05 1981-09-07 Procédé et appareil pour la délignification à l'oxygène de pâte Ceased EP0047656A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US18451480A 1980-09-05 1980-09-05
US184514 1988-04-21

Publications (1)

Publication Number Publication Date
EP0047656A1 true EP0047656A1 (fr) 1982-03-17

Family

ID=22677195

Family Applications (1)

Application Number Title Priority Date Filing Date
EP81304078A Ceased EP0047656A1 (fr) 1980-09-05 1981-09-07 Procédé et appareil pour la délignification à l'oxygène de pâte

Country Status (8)

Country Link
EP (1) EP0047656A1 (fr)
JP (1) JPS57121687A (fr)
AU (1) AU543014B2 (fr)
CA (1) CA1176408A (fr)
ES (1) ES505210A0 (fr)
FI (1) FI812725L (fr)
NO (1) NO813009L (fr)
ZA (1) ZA816105B (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1992012288A1 (fr) * 1991-01-03 1992-07-23 Union Camp Patent Holding, Inc. Addition de substance alcaline en deux etapes pour une delignification a base d'oxygene d'une pate a consistance elevee
US5525195A (en) * 1989-02-15 1996-06-11 Union Camp Patent Holding, Inc. Process for high consistency delignification using a low consistency alkali pretreatment
US5672247A (en) * 1995-03-03 1997-09-30 Union Camp Patent Holding, Inc. Control scheme for rapid pulp delignification and bleaching
US5736004A (en) * 1995-03-03 1998-04-07 Union Camp Patent Holding, Inc. Control scheme for rapid pulp delignification and bleaching

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA918978A (en) * 1970-01-08 1973-01-16 G. Jamieson Allan Oxygen bleaching
JPS5119481B2 (fr) * 1973-08-30 1976-06-17
US4363697A (en) * 1979-12-03 1982-12-14 The Black Clawson Company Method for medium consistency oxygen delignification of pulp

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
None

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5525195A (en) * 1989-02-15 1996-06-11 Union Camp Patent Holding, Inc. Process for high consistency delignification using a low consistency alkali pretreatment
WO1992012288A1 (fr) * 1991-01-03 1992-07-23 Union Camp Patent Holding, Inc. Addition de substance alcaline en deux etapes pour une delignification a base d'oxygene d'une pate a consistance elevee
US5672247A (en) * 1995-03-03 1997-09-30 Union Camp Patent Holding, Inc. Control scheme for rapid pulp delignification and bleaching
US5736004A (en) * 1995-03-03 1998-04-07 Union Camp Patent Holding, Inc. Control scheme for rapid pulp delignification and bleaching

Also Published As

Publication number Publication date
AU543014B2 (en) 1985-03-28
CA1176408A (fr) 1984-10-23
ES8205285A1 (es) 1982-06-01
FI812725L (fi) 1982-03-06
ES505210A0 (es) 1982-06-01
JPS57121687A (en) 1982-07-29
NO813009L (no) 1982-03-08
ZA816105B (en) 1982-09-29
AU7492281A (en) 1982-03-11

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Inventor name: MAGNOTTA, VINCENT L.

Inventor name: ELTON, EDWARD F.