US3811994A - Method of continuous cellulose digestion and digester adapted for performing the method - Google Patents

Method of continuous cellulose digestion and digester adapted for performing the method Download PDF

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Publication number
US3811994A
US3811994A US00157855A US15785571A US3811994A US 3811994 A US3811994 A US 3811994A US 00157855 A US00157855 A US 00157855A US 15785571 A US15785571 A US 15785571A US 3811994 A US3811994 A US 3811994A
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Prior art keywords
zone
digester
digesting
liquor
temperature
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Expired - Lifetime
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US00157855A
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English (en)
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B Ostberg
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Metso Fiber Karlstad AB
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Kamyr AB
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    • 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
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/22—Other features of pulping processes
    • D21C3/24—Continuous processes
    • 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
    • D21C7/00—Digesters

Definitions

  • the invention relates to a method of continuous cellulose digestion wherein a coherent column of chips or other finely comminuted fiber material mixed with a digesting liquor, such as sulphate or sulphite liquor, during its continuous downward motion through an upright digester is caused to pass first through a zone where the fiber material is impregnated with digesting liquor at a comparatively low temperature and then through a digesting zone where a temperature is maintained which is suitable for the dissolution of the lignin contents of the fiber material.
  • a digesting liquor such as sulphate or sulphite liquor
  • the object of the invention is to keep the impregnating zone and the digesting zone carefully separated in temperature respects as far as possible and thus to prevent sibly chips emanating from the digesting zone and caused by the tendency of convection of the digesting liquor due to the temperature inversion in the top end of the digester.
  • said object is reached without significant influence upon the impregnation or the digestion by maintaining in a thin layer at the lower .part of the impregnating zone an essentially horizontal flow of liquid over the entire cross-section of the chips column, viz by extracting liquid at the periphery of the chips column, cooling the same in an exterior circulation loop and returning said liquid to the center of the chips column.
  • the invention also relates to a digester adapted for performing said method, which digester is characterized essentially in that between its upper end provided with a chips feeding device, and a lower zone where the digesting liquor is heated to the full digesting temperature by circulation through an outer loop, there is arranged a liquid circulation loop comprising a strainer inserted in the digester shell, an exterior conduit connected thereto, in which a pump and a cooling means are included, and an interior conduit having an orifice located at the center of the digester cross-section.
  • FIG. 1 diagrammatically shows an embodiment of the digester according to the invention
  • FIG. 2 shows a modified embodiment of the top of the digester.
  • the digester shown in FIG. 1 is mainly of standard design, thus consisting of a standing cylindrical container 11 which preferably widens slightly in the downward direction and which is adapted for continuous downward motion of chips or other finely comminuted fiber material mixed with digesting liquor, e.g. sulphate or sulphite liquor, in such a quantity that the mixture moves as a coherent column without turbulence or significant interior eddies or convulsions.
  • the length of the digester is divided into an impregnating zone a, a digesting zone b, and a washing zone 0.
  • a charging device comprising a screw feeder 13 and a surrounding cylindrical strainer 15.
  • a fluent mixture of chips and digesting liquor having a temperature of preferably about IOU- C. is supplied through a conduit 17 to the upper end of the feeder screw, and excess of liquid departs through the strainer 13 and the return conduit 19 connected to the space outside said strainer, whereas the thickened chips suspension which may have a liquid to wood ratio of 1.5-3.5 :1, slowly moves on down into the digester without any relative motion of liquor and chips.
  • the chips are impregnated with digesting liquor at the operating pressure of the digester which may be 7 to 15 atmospheres overpressure, preferably about 10 atmospheres overpressure.
  • the length of the impregnating zone and the feeding speed are so chosen that the impregnation is extended over a time period of 10 to 60 minutes, preferably about 25 minutes. During said period the digesting chemicals gradually dilfuse into the chips, so that the concentration of the free liquor drops towards the lower end of the impregnating zone.
  • washing of the digested pulp takes place before the same is transferred by means of a discharging device 37 to the pulp outlet conduit 39.
  • the discharge is connected with lowering of the pressure and usually also dilution.
  • the wash is performed by cool wash water supplied close to the pulp outlet as at 39a and forced upwardly through the digester in countercurrent to the pulp. Wash water is withdrawn through a strainer 41 and is pumped through a heating device 43 and an interior tube 45 back to the center of the digester section, where the heated wash liquid is spread radially and distributed over the pulp column. Said heated wash water then performs a second step c f the washing of the pulp, while displacing the spent liquor towards and out through the strainer 33.
  • a radial equalization circulation is maintained by withdrawing liquid through a strainer girdle 47 and pumping the same back by means of the pump 49 through the tube 51 to the center of the digester at a level slightly above the strainer 47.
  • said measures consist in maintaining over the entire cross-section of the chips column and in a thin layer closely above the strainers 21, 23 a radial and essentially horizontal flow of centrally supplied liquid having been cooled in an exterior circulation loop.
  • the digester is provided with a strainer girdle 53 for withdrawal of liquid at the periphery of the digester and with a central tube 55 for returning said liquid to the center of the digester cross-section and approximately at the level of the strainer 53 or slightly above the same.
  • the pump 57 the liquid withdrawn by the strainer 53 is caused to flow in an exterior circulation loop comprising a heat exchanger 59 and is then returned to the digester.
  • the heat exchanger 59 functions as a cooler, its secondary side being connected to a conduit 61 carrying cool water or cool liquor.
  • the same quantity of liquid as is withdrawn, is returned in said loop to the digester, i.e. without addition of liquor or dilution and also without draining or evaporation taking place in said loop.
  • the pump 57 is a low-pressure pump that merely has to supply the pressure differential corresponding to the flow resistance in the conduits.
  • a valve 63 inserted in the conduit 64 carrying the cooling liquid is controlled by a temperature sensing instrument 65 so that the temperature of the liquid in the tube 55 is maintained at a desired value. Said temperature is preferably the same or slightly lower than the temperature of the chips-liquor-mixture supplied to the digester top.
  • said temperature is somewhat below 120 C.
  • the cooling circulation should be rather heavy and be chosen in a proper proportion to the quantity of the digesting liquor supplied to the digester per unit of time.
  • said quantity of cooled liquid per unit of time is at least equal to said first-mentioned quantity so that the entire quantity of supplied digesting liquor is withdrawn, cooled, and returned at least once, usually several times, before it passes on to the digesting zone.
  • Said heavy cross-flow which is concentrated to a comparatively thin layer will carry with it such digesting liquor of higher temperature as locally and due to convection has penetrated up into said layer, and therefore convection currents cannot enter into zone a and heat said zone locally and uncontrollably.
  • any such convection currents will heat the liquid withdrawn by the strainer 53, but said heat is removed by the cooling taking place in the cooler 59 and will not affect the impregnation. Therefore, the impregnation temperature can be maintained uniform from the digester top to the level where the digesting zone b begins.
  • a small transition zone will be present between the strainers 53 and 21 but said zone can be held quite small by placing the strainers close together.
  • the orifice of the conduit 55 for supply of cooled liquid should be placed above the orifice of the conduit 31 for supply of heated digested liquor and at a distance therefrom, measured in the axial direction, which is considerably less than strainerto the strainer 21 or to the orifice of the conduit 31 for supply of heated digesting liquor.
  • the orifice of the conduit 55 for cooled liquid is situated approximately at the level of the corresponding withdrawal strainer 53. Considering the motion of the chips column it is preferable, however, to place said orifice ,somewhat higher, i.e. upstream of said strainer,. but
  • the modified digester top shown in *FIG. 2 corres nds to the embodiment shown in FIG. 1 in respect of charging device, cooling circulation, and heating circulation, and the same reference numerals have been used for corresponding details.
  • the difference consists in that the impregnating zone a has been made longer and narrower in comparison to the standard design of the FIG. 1.
  • the diameter d of the cylindrical top may be about 12 feet (3.65 meters) over a length of about 32 feet (9.8 meters).
  • A-conical shell part 67 joins the narrow top to the lower widened shell part 11 of the digester.
  • the strainer 53 pertaining to the cooling circulation is located at the lower end of the slim top, and the strainer 21 pertaining to the heating circulation is located at the upper end of the wider cylindrical shell part 11 of the digester.
  • the diameter of the digester top is considerably less than the diameter of the rest of the digester, the reduction being about 25%.
  • a reduction of the diameter as low as 15-20% or still less will be etIective, and of course, a reduction greater than 25% may be chosen, although the top then has to be made inconveniently long for a complete impregnation of the chips therein.
  • the design of the digester with a long slim top also involves that the capacity of the cooler 59 can be reduced.
  • the heating of the fiber material to digesting temperature is performed by withdrawal of liquid from the fiber material, heating the same in an exterior circulation loop and returning said liquid to the digester, the improvement consisting in that the supply of circulating cooled liquid takes place at a point situated above the point of supply of heated liquid and at a distance therefrom considerably less or not greater than /3 of the distance to the digester top.

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US00157855A 1970-06-29 1971-06-29 Method of continuous cellulose digestion and digester adapted for performing the method Expired - Lifetime US3811994A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE9004/70A SE343344B (no) 1970-06-29 1970-06-29

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US3811994A true US3811994A (en) 1974-05-21

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US00157855A Expired - Lifetime US3811994A (en) 1970-06-29 1971-06-29 Method of continuous cellulose digestion and digester adapted for performing the method

Country Status (8)

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US (1) US3811994A (no)
JP (1) JPS5034641B1 (no)
CA (1) CA938820A (no)
DE (1) DE2132116C3 (no)
FI (1) FI52366C (no)
FR (1) FR2100030A5 (no)
NO (1) NO130733C (no)
SE (1) SE343344B (no)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3941650A (en) * 1974-08-09 1976-03-02 Schnyder Auxilius P Continuous digester
US4028171A (en) * 1974-07-05 1977-06-07 Kamyr Aktiebolag Method for continuous treatment of fiber material in a vertical array
US4071399A (en) * 1976-09-01 1978-01-31 Kamyr, Inc. Apparatus and method for the displacement impregnation of cellulosic chips material
US4221632A (en) * 1979-04-03 1980-09-09 Weyerhaeuser Company Method and apparatus for determining the location of the chip level in a pulping digester
US4547264A (en) * 1979-02-12 1985-10-15 Kamyr, Inc. Method of withdrawing liquid from a pair of vertically spaced annular screens
US4568419A (en) * 1984-02-27 1986-02-04 Laakso Oliver A Method of treating comminuted cellulosic fibrous material in a vertical vessel
US4693785A (en) * 1984-02-27 1987-09-15 Laakso Oliver A Digester having plural screens and means for controlling the liquid withdrawal
US5236554A (en) * 1991-08-16 1993-08-17 Kamyr, Inc. Digester having plural screens with means for controlling liquid injection and withdrawal
US5591303A (en) * 1992-11-18 1997-01-07 Kvaerner Pulping Technologies Ab Process for operating a digester
US5788812A (en) * 1985-11-05 1998-08-04 Agar; Richard C. Method of recovering furfural from organic pulping liquor
US5985096A (en) * 1997-09-23 1999-11-16 Ahlstrom Machinery Inc. Vertical pulping digester having substantially constant diameter
US6123808A (en) * 1997-12-09 2000-09-26 Ahlstrom Machinery Inc. Distribution of dilution liquor to the discharge of a cellulose pulp digester

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FI66215C (fi) * 1982-12-14 1984-09-10 Ekono Oy Saett vid kontinuerlig uppslutning av finfoerdelat cellulosahaltigt material

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4028171A (en) * 1974-07-05 1977-06-07 Kamyr Aktiebolag Method for continuous treatment of fiber material in a vertical array
US3941650A (en) * 1974-08-09 1976-03-02 Schnyder Auxilius P Continuous digester
US4071399A (en) * 1976-09-01 1978-01-31 Kamyr, Inc. Apparatus and method for the displacement impregnation of cellulosic chips material
US4547264A (en) * 1979-02-12 1985-10-15 Kamyr, Inc. Method of withdrawing liquid from a pair of vertically spaced annular screens
US4221632A (en) * 1979-04-03 1980-09-09 Weyerhaeuser Company Method and apparatus for determining the location of the chip level in a pulping digester
US4568419A (en) * 1984-02-27 1986-02-04 Laakso Oliver A Method of treating comminuted cellulosic fibrous material in a vertical vessel
US4693785A (en) * 1984-02-27 1987-09-15 Laakso Oliver A Digester having plural screens and means for controlling the liquid withdrawal
US5788812A (en) * 1985-11-05 1998-08-04 Agar; Richard C. Method of recovering furfural from organic pulping liquor
US5236554A (en) * 1991-08-16 1993-08-17 Kamyr, Inc. Digester having plural screens with means for controlling liquid injection and withdrawal
US5591303A (en) * 1992-11-18 1997-01-07 Kvaerner Pulping Technologies Ab Process for operating a digester
US5985096A (en) * 1997-09-23 1999-11-16 Ahlstrom Machinery Inc. Vertical pulping digester having substantially constant diameter
US6123808A (en) * 1997-12-09 2000-09-26 Ahlstrom Machinery Inc. Distribution of dilution liquor to the discharge of a cellulose pulp digester

Also Published As

Publication number Publication date
FR2100030A5 (no) 1972-03-17
NO130733C (no) 1975-01-29
FI52366C (fi) 1977-08-10
DE2132116A1 (de) 1972-01-05
CA938820A (en) 1973-12-25
SE343344B (no) 1972-03-06
DE2132116C3 (de) 1973-12-13
NO130733B (no) 1974-10-21
DE2132116B2 (de) 1973-05-10
FI52366B (no) 1977-05-02
JPS5034641B1 (no) 1975-11-10

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