US3425898A - Two stage chemical digestion within a single vessel with wash between stages - Google Patents

Two stage chemical digestion within a single vessel with wash between stages Download PDF

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Publication number
US3425898A
US3425898A US417945A US3425898DA US3425898A US 3425898 A US3425898 A US 3425898A US 417945 A US417945 A US 417945A US 3425898D A US3425898D A US 3425898DA US 3425898 A US3425898 A US 3425898A
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stage
sieve
girdle
vessel
conduit
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US417945A
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Oliver Armas Laakso
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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
    • 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
    • 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
    • D21C3/26—Multistage processes

Definitions

  • the present invention relates to a method of performing a two stage chemical treatment on cellulosic fibrous material during passage thereof through la continuous digester.
  • the invention also relates to improvements in continuous digestion apparatus for performing a two stage chemical treatment on cellulosic fibrous material passing therethrough.
  • a two stage chemical treatment is one in which each stage is independent of the other to the extent that different chemical treatments, e.g., digestion and bleaching, may be performed in each stage without interference from the other, although the invention is equally applicable to the'use of two chemical treatments that are mutually miscible, e.g., two-stage digestion. It is a feature of the invention that the two chemicals employed may be of widely divergent chemical and physical properties, and that treatments therewith may be carried out continuously and simultaneously in one and the same continuous digestion vessel.
  • Two stage continuous digesters are known wherein a cellulosic fibrous material feed may be subjected to first digestion treatment and a second digestion treatment.
  • Such devices present a problem in that it is not possible to simultaneously treat cellulosic fibrous material with two different chemical treatments in one and the same pressure-resistant digestion vessel, while the cellulosic fibrous material is fed continuously therethrough.
  • Longitudinal pressure-resistant digestion vessels are known in the art which have a substantially uniform cross-section and are provided with means for continuous feed of fibrous material into one end and for ydischarge thereof out of the other end.
  • Such vessels have ICC hithereto not been provided with further means for supplying and withdrawing treating liquids of two different kinds at spaced points along the length of the vessel such that until now it has not been possible to perform a two-stage chemical treatment, particularly digestion and/or bleaching of cellulosic fibrous material that is continuously passing through the vessel.
  • ⁇ It is therefore the object of the present invention to provide to a method of performing a two-stage chemical treatment on cellulosic fibrous material while it is fed continuously through a pressure-resistant digestion vessel wherein the two treatment stages are independent of each other, so that it is possible to separately and simultaneously treat the cellulosic material with two different liquids that may be so different that mixing of them would involve difficulties, e.g., inter-reactions, that are desired to be prevented.
  • the foregoing objects are achieved according to the invention by supplying Wash liquid at a place located between the two treatment stages and in an amount sufiicient to cause a wash liquid fiow countercurrent to the direction of feed of the fibrous material to thereby displace the treatment liquid of the first stage and wash out the first stage treatment liquid before the fibrous material reaches the zone where it will be contacted by the treatment liquid of the second stage.
  • the objects of the invention are achieved by providing a two-stage digestion vessel with means for supply of wash liquid and for spreading the same over the entire cross-section of the vessel.
  • such means are disposed in a zone of the vessel located between sieve girdles which are mutually spaced apart along the longitudinal direction of the vessel and each being adapted for the extraction from the fibrous material of a different kind of spent treatment liquid.
  • FIGURES 1 and 2 diagrammatically show two embodiments of the invention that are each adapted for performing the above-mentioned two-stage treatment of cellulosic fibrous material.
  • the reference numeral 11 designates an upright cylindrical pressure-resistant vessel of a substantially uniform cross-sectional area ⁇ and a length of the order -of l0 times its diameter.
  • the vessel is provided with charging means or feeding devcie 13, the construction of which is well known in the art such as from Patent No. 2,459,180, and accordingly need not be described here.
  • a comminuted cellulosic fibrous material such as wood chips, is charged into the vessel either continuously or as small successive batches.
  • the fibrous material moves vertically downwards through the vessel, taking the form of a rigid Column and is discharged at the lower end of the vessel into a conduit 15 by the aid of discharging means which are also well known and therefore not shown yor described herein.
  • the direction of feed of the fibrous material is indicated by double arrows 17.
  • the column of fibrous material is subjected to various treatments which take place in separate zones denoted by the reference letters a, b, c, d and e.
  • the chips are impregnated with digesting liquor fed into the vessel together with the chips, as indicated by the arrow 19.
  • This liquor which is provided for the first stage of delignifying digestion of the fibrous material, may preferably consist -of sulphite liquor, e.g., sodium or calcium sulphite liquor.
  • the first digesting liquor in this zone a moves concurrently with the fiber material.
  • the extracted liquor is then circulated by means of pump 25 in the first exterior conduit shown.
  • This conduit is provided with a heating devi-ce 2.7 which is connected to an interior tube 29 extending along the axis of the digestion vessel 11 and having an orifice at or slightly above the level of the sieve girdle 23.
  • the withdrawn liquor which has been heatedin the heating device 27 by first stage steam supplied thereto through conduit 31, is spread from the orifice of the tube 29 radially outwards and causes the column of fibrous material to be brought to the proper digesting temperature.
  • the heating may take place by injecting steam directly into the digestion vessel 11 or into the circulation conduit.
  • the first stage of digestion atkes place in the zone b, below the heating and impregnating zone a, so that when the fibrous material reaches the level of the second sieve girdle 33 inserted into the shell of the vessel 11, the first digesting liquor fed concurrently with the chips is almost entirely spent or depleted and the chemical treatment of the chips by the same is completed.
  • the spent liquor is drawn off throught the sieve girdle 33 and a part thereof is pumped into the above-described first circulation loop by means of a pump 35 and is thus returned to the vessel through the orifice of the tube 29, whereas another part 4of the spent liquor is discharged through a conduit 37, e.g. leading to a plant for recovery of the heat and chemical values of the liquor.
  • the liquor in zone b also moves concurrently with the fibrous material.
  • the shell of the vessel 11 is provided with a third sieve girdle 40.
  • the two last-mentioned sieve girdles 33 and 40 are situated at a distance from the charging end of the vessel approximating from one fourth to one half of the total length of the vessel and preferably about one third thereof.
  • a second exterior conduit 42 Connected to the sieve girdle 40 is a second exterior conduit 42 which in its turn is connected to an interior conduit 44 extending along the axis of the vessel 11 and having its orifice situated at the level of the sieve girdle 40 or at a somewhat higher level.
  • a pump 46 inserted in the conduit 42 maintains a circulating flow in the second circulation loop thus formed.
  • a conduit 43 To this last-mentioned circulation loop there is also connected a conduit 43 through which a first wash liquid is supplied.
  • the first wash liquid may consist of clean water or of such white water as is obtained as filtrate from a wash filter upon which the pulp is washed after its discharge out of the vessel 11.
  • the first wash water is spread radially outwards towards the sieve girdle 40 and thus is distributed over the entire cross-section of the vessel.
  • Such a great amount of wash water is supplied through the conduit 48, that from the level of the sieve girdle 40, an upwardly directed iiow of liquid, i.e. a flow counter-current to the direction of movement ⁇ of the brous material is formed which flow passes through the fibrous material and towards the sieve girdle 33. Therefore, in its movement through the zone c, the downwardly flowing fibrous material encounters a flow of wash liquid which washes out with it any digesting liquor still remaining in the fibrous material after the latter has moved past the sieve girdle 33.
  • the wall of the vessel is provided with a fourth sieve girdle 41 whi-ch is inserted closely underneath the sieve girdle 40.
  • Sieve girdle 41 serves to relieve the fibrous material of such spent digesting liquor as has been used for a second stage of delignifying digestion in the zone d.
  • the second stage delignifying and digesting liquor may be introduced with a force suiiicient to move it upwardly and countercurrently to the direction of movement of the fibrous material, as indicated by the arrows 43.
  • the second stage digesting liquor encounters an oppositely directe-d fiow of liquid, such that the second stage digesting liquor must be drawn off through the sieve girdle 41. lt is then evident that a stagnant border layer exists between the sieve girdles 33 and 41 at a region formed by the converging of the oppositely directed liquid iiow patterns.
  • the first wash water from the conduit 48 may penetrate downwardly and bring with it residues of the digesting liquor of the second stage towards the sieve girdle 41, or the residues of the digesting liquor of the second stage may be carried with the liquid circulating in the second circulation loop 40-46-42-44 and discharged through the sieve girdle 33.
  • the second digesting zone d extends from the sieve girdle 41 to a fifth sieve girdle 45 which is situated at a distance from the outlet end of the vessel 11 amounting approximately to one third of the vessel length.
  • Sieve girdle 45 is connected into a third circulation loop comprising a heat exchanger 47 and a tube 49 located centrally of the vessel and having at its end an orifice situated at the level of the sieve girdle 45 or somewhat higher.
  • the pump 51 brings the liquid to circulate in thsi third circulation loop, and chemicals coming from the conduit 53 and required for the second digesting stage, e.g. sulphate liquor or SO2, are charged into this third circulation loop.
  • Second stage steam from the conduit 55 is supplied to the heating device 47 in order to heat the circulating liquid to the temperature required for the second digesting stage.
  • Second stage wash liquid which usually consists either of water or of filtrate coming from a filter washing plant and containing residues of digesting liquor.
  • the second stage wash liquid is supplied through spray nozzles 57 distributed around the pulp outlet 59 of the vessel 11.
  • the second stage wash liquid displaces the second stage digesting liquor spread from the orifice of the tube 49 and forces the second stage digesting liquor to move upwardly and countercurrent (arrows 43) to the movement of fibrous material (arrows 17).
  • the second stage digesting liquor ow encounters the first stage wash water supplied through the orifice of the conduit 44, whereby the second stage digesting liquor, possibly in admixture with first stage wash liquid, is forced to depart through the sieve girdle 41.
  • wash liquid is led to a tank 63, eg., a cyclone, in which a pressure considerably reduced in comparison to the digester pressure is maintained and from which the released steam or gas is carried ofi through the conduit 65 to a device (not shown) for recovery of heat therein, whereas the spent liquor is led through the conduit 67 to a plant for recovery of the chemicals therein.
  • a tank 63 eg., a cyclone
  • the apparatus or digestion plant shown in FIGURE 2 corresponds in large part to the plant shown in FIGURE 1, and the same reference numerals have accordingly been employed to denote the same or similar corresponding parts.
  • the various circulation loops are provided with different piping arrangements for clarity, although their operation remains unchanged.
  • the zones a, b and c serve for impregnation, delignifying digestion and counter-current wash, respectively.
  • a further sieve girdle 34 has been added which is situated closely below the sieve girdle 33t.
  • sieve girdle 34 Connected to sieve girdle 34 is an intermediate circulation loop consisting of the exterior conduit 28 with pump 30 and an interior conduit 32 which extends along the axis of the vessel 11 and has an end orifice situated at the level of the sieve girdle 33 or somewhat higher. Due to the circulation in the intermediate circulation loop, a heavy radial flow is maintained in the section lying between the sieve girdles 33 and 34, whereby the removal of the rst digesting liquor through the sieve girdle 33 becomes still more complete. The spent digesting liquor departs through the conduit 37 to a tank, e.g.
  • the fibrous material is completely delignified during treatment in the zone b, and the operation performed in zone d consists of a bleaching operation brought about by a solvent which is volatile at atmospheric pressure Ibut is in liquid form at the pressure prevailing in the
  • This solvent is supplied through the conduit 53.
  • the heat exchanger -47 which in this case is inserted in the conduit connecting the sieve girdle 41 to the cyclone 63, transfers heat to the solvent circulating in the third circulation loop 4S-51-47-49. From the end of tube 49, the solvent moves upwardly counter-current to the direction of the fibrous material or pulp and towards the sieve girdle 41, while dissolving coloring substances in the pulp.
  • the main part of the solvent departs through the sieve girdle 41 to the tank 63 in which a lower pressure is maintained, so that the solvent evaporates.
  • the solvent is separated from the products dissolved thereby, and the solvent is then returned for repeated use in the vessel 11.
  • the apparatus illustrated in FIGURES 1 and 2 is also susceptible to another modification which consists in that the second stage cool wash water supplied through the nozzles 57 to the lowermost end of the vessel 11, is discharged through a further lowermost sieve girdle 50 and is carried by a pump 52 through an outer conduit 54 in which the heat exchanger 26 is inserted, back to an inner conduit 56 which lets out the heated water through its open end located approximately -at the level of the sieve girdle 50, thereby raising the temperature of the second stage wash water to a temperature that is favorable for the washing in zone e.
  • the foregoing description is illustrative rather than limiting on the invention, and that various changes and modifications may be made without departing from the spirit of the invention. Accordingly, the invention is not limited to the specific types of chemicals suggested for use in the two digestion stages, but can equally well be applied to presently lknown chemicals, and may be susceptible to use with chemicals and procedures yet to be developed. Hence, the invention is applicable to substantially any two-stage digesting or bleaching or combined digesting-bleaching method which can be performed in one and the same vessel with regard to the restrictions involved.
  • a method for performing two successive treatments of fibrous material in two mutually exclusive treatment stages spaced axially from one another within a single vessel comprising the steps of:
  • a continuous digester comprising a longitudinal pressure-resistant vessel having a substantially uniform cross section, means for continuously feeding cellulosic fibrous material into an up-stream end thereof and through said vessel; means for discharging the cellulosic fibrous material from a down-stream end thereof; a rst conduit having orifice means for supplying a lirst treating liquid to the vessel and first sieve girdle means down-stream in respect to the movement of the said cellulosic fibrous material of said first conduit orifice means for withdrawing at least a part of the first treating liquid from the vessel; a second conduit having orifice means spaced down-stream in respect to the movement of the said cellulosic brous material from the said rst sieve girdle means for supplying a second treating liquid to the vessels; and second sieve girdle means for withdrawing the second treating liquid from the vessel, the said second sieve girdle means being located down-stream in respect to the movement of the said cellulosic material
  • the apparatus of claim 4 including sixth Sieve girdle means disposed above said fifth sieve girdle means and a seventh sieve girdle means disposed below the said fifth sieve girdle means, said further sieve girdle means being connected to respective intermediate circulation loops lwhereby the rst and second treating liquids are respectively substantially completely withdrawn.
  • the apparatus of claim 4 including a lowermost sieve girdle for withdrawing a second wash liqfuid which is supplied to said apparatus adjacent said discharge means.

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US417945A 1963-12-13 1964-12-14 Two stage chemical digestion within a single vessel with wash between stages Expired - Lifetime US3425898A (en)

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3595038A (en) * 1967-06-20 1971-07-27 Svenska Cellulosa Ab Apparatus for washing fibrous suspensions
US3874991A (en) * 1968-08-23 1975-04-01 Westvaco Corp Polysulfide impregnation of lignocellulosic materials in a continuous digester
US5080755A (en) * 1988-12-20 1992-01-14 Kamyr Ab Process for the continuous digestion of cellulosic fiber material
US5192396A (en) * 1988-12-20 1993-03-09 Kamyr Ab Process for the continuous digestion of cellulosic fiber material
AU639109B2 (en) * 1990-08-17 1993-07-15 Kamyr Inc. Sulfite modified continuous digesting
US5547012A (en) * 1993-05-04 1996-08-20 Kamyr, Inc. Dissolved solids control in pulp production
US5849151A (en) * 1993-05-04 1998-12-15 Ahlstrom Machinery Inc. Continuous digester having means for implementing low dissolved solids profiling
AU704580B2 (en) * 1993-05-04 1999-04-29 Kamyr Inc. Dissolved solids control in pulp protection
US5985096A (en) * 1997-09-23 1999-11-16 Ahlstrom Machinery Inc. Vertical pulping digester having substantially constant diameter
US6332950B1 (en) * 1997-06-25 2001-12-25 Kaverner Pulping Ab Method in connection with the pretreatment of comminuted fibrous material

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US942403A (en) * 1908-11-25 1909-12-07 John H Mccoy Apparatus for distributing building material.
US1683262A (en) * 1927-04-19 1928-09-04 Brown Co Process of chemically treating and washing pulp
US2772138A (en) * 1952-12-31 1956-11-27 Hercules Powder Co Ltd Continuous bleaching process
US3081218A (en) * 1960-03-18 1963-03-12 Harold R Ambuehl Continuous pulping process for the production of paper products
US3200032A (en) * 1961-12-23 1965-08-10 Kamyr Ab Continuous process for digesting cellulosic material
US3298899A (en) * 1962-03-03 1967-01-17 Kamyr Ab Method and arrangement for washing and cooling at the outlet end of a continuous cellulose digester
US3303088A (en) * 1963-04-19 1967-02-07 Lummus Co Continuous liquid-phase rapid pulping

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US942403A (en) * 1908-11-25 1909-12-07 John H Mccoy Apparatus for distributing building material.
US1683262A (en) * 1927-04-19 1928-09-04 Brown Co Process of chemically treating and washing pulp
US2772138A (en) * 1952-12-31 1956-11-27 Hercules Powder Co Ltd Continuous bleaching process
US3081218A (en) * 1960-03-18 1963-03-12 Harold R Ambuehl Continuous pulping process for the production of paper products
US3200032A (en) * 1961-12-23 1965-08-10 Kamyr Ab Continuous process for digesting cellulosic material
US3298899A (en) * 1962-03-03 1967-01-17 Kamyr Ab Method and arrangement for washing and cooling at the outlet end of a continuous cellulose digester
US3303088A (en) * 1963-04-19 1967-02-07 Lummus Co Continuous liquid-phase rapid pulping

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3595038A (en) * 1967-06-20 1971-07-27 Svenska Cellulosa Ab Apparatus for washing fibrous suspensions
US3874991A (en) * 1968-08-23 1975-04-01 Westvaco Corp Polysulfide impregnation of lignocellulosic materials in a continuous digester
US5080755A (en) * 1988-12-20 1992-01-14 Kamyr Ab Process for the continuous digestion of cellulosic fiber material
US5192396A (en) * 1988-12-20 1993-03-09 Kamyr Ab Process for the continuous digestion of cellulosic fiber material
AU639109B2 (en) * 1990-08-17 1993-07-15 Kamyr Inc. Sulfite modified continuous digesting
US5849150A (en) * 1993-05-04 1998-12-15 Ahlstrom Machinery Inc. Low dissolved solids control in pulp production
AU690105B2 (en) * 1993-05-04 1998-04-23 Kamyr Inc. Dissolved solids control in pulp production
US5849151A (en) * 1993-05-04 1998-12-15 Ahlstrom Machinery Inc. Continuous digester having means for implementing low dissolved solids profiling
US5547012A (en) * 1993-05-04 1996-08-20 Kamyr, Inc. Dissolved solids control in pulp production
AU704580B2 (en) * 1993-05-04 1999-04-29 Kamyr Inc. Dissolved solids control in pulp protection
AU721103B2 (en) * 1993-05-04 2000-06-22 Kamyr Inc. Dissolved solids control in pulp protection
US6159337A (en) * 1993-05-04 2000-12-12 Andritz-Ahlstrom Inc. Dissolved organic materials control in cellulose pulp production
US6280568B1 (en) 1993-05-04 2001-08-28 Andritz-Ahlstrom Inc. Dissolved organic material control in a cellulose pulp continuous digester
EP1873303A3 (en) * 1993-05-04 2008-06-18 Andritz Inc. Dissolved solids control in pulp production
US6332950B1 (en) * 1997-06-25 2001-12-25 Kaverner Pulping Ab Method in connection with the pretreatment of comminuted fibrous material
US5985096A (en) * 1997-09-23 1999-11-16 Ahlstrom Machinery Inc. Vertical pulping digester having substantially constant diameter

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DE1517149A1 (de) 1969-03-13
FI44514B (ja) 1971-08-02

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