US3652384A - Countercurrent pulping of cellulosic materials including regulation of active chemical therein - Google Patents

Countercurrent pulping of cellulosic materials including regulation of active chemical therein Download PDF

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Publication number
US3652384A
US3652384A US74513A US3652384DA US3652384A US 3652384 A US3652384 A US 3652384A US 74513 A US74513 A US 74513A US 3652384D A US3652384D A US 3652384DA US 3652384 A US3652384 A US 3652384A
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Prior art keywords
digester
point
chemical
liquor
active chemical
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US74513A
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English (en)
Inventor
Arthur Raymond Sloman
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Associated Pulp and Paper Mills Ltd
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Associated Pulp and Paper Mills Ltd
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Priority claimed from AU7439/66A external-priority patent/AU295860B2/en
Application filed by Associated Pulp and Paper Mills Ltd filed Critical Associated Pulp and Paper Mills Ltd
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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
    • D21C3/228—Automation of the pulping processes

Definitions

  • ABSTRACT A method is disclosed for the continuous treatment of wood chips in a downflow vertical digester by the alkaline process. Wood chips and black liquor are introduced near the upper end of the digester and travel downwardly therethrough to a sole point at which the black liquor is discharged from the digester.
  • Cooking liquor is introduced at a point between the lower end and black liquor discharge point of the digester and passes upwardly to the discharge point, countercurrent to the flow of wood chips, to cook the chips and leave the digester as back liquor at the discharge point.
  • the cooked wood chips are removed from the lower end of the digester.
  • the active chemical in the cooking liquor is maintained constant.
  • Active chemical is further added near the upper end of the digester and the addition thereof is regulated in response to changes in the residual active chemical in the black liquor which are monitored at the discharge point of the digester, in order to keep the residual active chemical in the discharged black liquor at a substantially constant concentration.
  • the quantity of active chemical added near the upper end of the digester does not exceed 20 percent of the total active chemical added to the digester.
  • This invention relates to a method temperatures, which comprises feeding the wood in subdivided form to an entry point of the digester and causing same to move through the digester to a discharge point, the wood being caused to move in succession through a cooking zone and a diffusion-displacement zone in the digester, subjecting the wood to a cooking treatment in the cooking zone by means of an alkaline cooking liquor containing active chemical which is introduced into the digester at a point where the wood is substantially cooked, causing the cooking liquor to pass through the cooking zone in a direction countercurrent to the movement of wood thcrethrough, subjecting the substantially cooked wood to a diffusion-displacement treatment in the diffusion-displacement zone by means of water which is introduced into the digester at a point between the point of entry of the cooking liquor and the point of discharge of the cooked wood from the digester, causing the water to pass through the diffusion-displacement zone and the cooking zone in a direction countercurrent to the movement of wood therethrough, discharging black liquor from the digester at a point between the point of entry
  • the cellulosic raw material is introduced at one end, for example the top, of a digester vessel, and the chemical in aqueous solution for digesting or cooking the material is introduced at a point between the point of entry of the raw material and the point of discharge of the digested material.
  • Water or other washing fluid is introduced at or near the point of discharge of the digested and washed material.
  • the water or other washing fluid in controlled amount flows in a direction opposite to that of the cellulosic material, and at or near the point of entry of the cooking chemical the chemical and washing fluid are mixed and heated and flow in a direction opposite to that of the cellulosic material.
  • the combined digesting and washing fluid and chemicals and substances dissolved therein leave the digester vessel at a point between the point of entry of the raw material and the point of entry of the cooking chemical.
  • alkali which term is used in this specification to include caustic soda and other cooking chemicals used in the said processes
  • extractives consisting of material soluble in hot water and/or dilute alkali.
  • Extractives are neutralized by alkali present in the digesting liquors which have already passed through the section of the process in which lignin has been treated, and to secure maximum utilization of the original chemical introduced to the process the rate of addition of digesting chemical is maintained at such a value that at the point of discharge of the liquors from the vessel the alkali concentration is very low. If the raw material entering the digester changes in composition so that its requirement of alkali or other cooking chemical changes, then the concentration of active chemical in the liquor discharged from the vessel increases or decreases. ln the case of an increase in concentration more chemical has been present during the reactions than'was necessary, and the pulp will tend to be overcooked; in the case where the concentration decreases, less chemical has been present than necessary and the pulp will be undercooked. To correct this position the rate of addition of cooking chemical is decreased or increased, but it will be clear that some time will be required before the system again reaches a steady state, producing pulp of satisfactory quality and with the concentration of residual alkali in the discharged cooking liquor at the required level.
  • the concentration of active chemical in the cooking liquor is much greater at a point just prior to the liquor reaching the discharge point for the liquor, and it has been found that the reaction rate in terms of rate of neutralization of alkali in the delignification section of the digestion is much slower and is a function of the concentration of active chemical present during these reactions.
  • the materials present in the wood which are involved in the delignification reactions neutralize relatively much smaller amounts of chemical. For example, in the case of eucalyptus woods, such materials neutralize approximately 4 to 5 percent NaOH/o.d. wood.
  • the process can then be operated so that the cellulosic material, after the extractives neutralization, enters the delignification zone with the extractives substantially neutralized at all times.
  • This prevents any substantial movement of the position of the notional interface between the extractives neutralization zone and the delignification zone, and the rate of the main addition of cooking chemical can be maintained substantially constant because the gradient of concentration of cooking chemical in the delignification zone is now substantially constant and unaffected by changes in the demand for chemical arising from changes in extractive content in the raw material entering the system.
  • not less than percent of total chemical required for pulping the raw material to the desired state is preferably added at the point where delignification is substantially complete, and the rate of addition of chemical at this point is maintained substantially constant for a substantially constant rate of addition of raw material and substantially constant temperature of cooking liquor.
  • Corrective" chemical is then added in amount preferably not greater than 20 percent of the total alkali addition, near the point of discharge of black liquor, either with the raw material at entry or otherwise, in quantity sufficient to ensure that the residual active chemical in the discharge liquor is maintained substantially constant.
  • FIGURE is a sectional view, partly broken away for convenience of illustration, showing a Kamyr type continuous digester which has been modified to enable the process of the present invention to be carried out therein.
  • the digester comprises a cylindrical pressure vessel 10 mounted with its axis vertical to the upper end of which the raw cellulosic material is added continuously or intermittently.
  • a cylindrical pressure vessel 10 mounted with its axis vertical to the upper end of which the raw cellulosic material is added continuously or intermittently.
  • wood in the form of chips as usually used in the industry is employed.
  • the wood chips are fed to the upper end 10a of the digester 10 as shown at +by means +in the art.
  • Black liquor is also fed to the upper end of the digester 10 as shown at 12, through supply line 12a and corrective alkali in the form of white liquor, which may be preheated, is added through supply line 16a and is mixed with the black liquor at 13.
  • the corrective alkali is added under the control of valve 26, as hereinafter described.
  • the digester 10 is provided at a point between its upper end and its midpoint with a set of upper internal screens 14 and a discharge outlet 15 for black liquor; and is provided at a point between its midpoint and its lower end with a liquor inlet 16 and with a set of lower internal screens 17.
  • Cooking alkali in the form of white liquor is introduced at or near point 16 and is heated, by means known in the art and not shown in the drawing, to the required temperature (say to C., usually about 180 C.). Heating of the incoming cooking liquor may be effected in various ways indirectly or by the addition of direct steam to the vessel.
  • a test cock 18 provided at a point below inlet 16. Cooked wood chips are discharged from the lower end of the vessel 10 through outlet 19 by means known in the art (not shown).
  • An inlet 20 is provided in the lower end of the digester 10 through which a washing fluid, usually water, may be introduced into the digester, said water or other washing fluid being supplied under pressure through a pipe line (not shown) and by means of a pump (not shown).
  • a washing fluid usually water
  • the section of the digester marked A in the drawing is referred to as the section in which the neutralization of extractives takes place, and the section of the digester marked B is that section where delignification reactions take place.
  • the horizontal dotted line D represents the notional interface between the zones A and B.
  • Section C of the digester is the section where countercurrent washing of the cooked wood chips occurs.
  • Water or other washing fluid is caused to flow upwardly in section C countercurrent to the downflow of wood chips and effects removal from the cooked wood chips of cooking chemical contained in the said chips passing downwardly through this zone.
  • Black liquor being discharged through outlet 15 is sampled through a cooled tube 21 and tested for its content of apparent active alkali by means of an automatic titrimeter 22.
  • the rate of addition of corrective alkali at 13 is regulated by means of valve 26 according to the apparent active alkali content of the black liquor discharging at 15 as determined by the titrimeter 22.
  • the aqueous pulp may be passed through a concentrator wherein more or less of the contained water is extracted from the pulp. This extracted water is or may be returned to the digester.
  • the degree of extraction of water from the discharged pulp is used to assist in regulating the upflow of water and liquor in the digester.
  • U is the net amount of water introduced into the digester at the bottom in gallons per minute
  • S is the rate of introduction of condensed steam with the wood expressed in gallons of water per minute
  • M is the rate of introduction of moisture in the wood in gallons per minute
  • W is the rate of introduction of cooking liquor in gallons per minute.
  • the rate of upflow of water in the digester is adjusted to not less than lT/Y gallons per minute, and preferably not less than 19T/Y gallons per minute, where T is the output of the digester in lbs. o.d. pulp per minute and Y is the percentage yield of unbleached pulp based on original o.d. wood fed to the digester.
  • prehydrolysis treatment in the digester prior to the cooking treatment. This may be effected by adding water or an aqueous acid solution to the digester at a point above the point of discharge of the black liquor and moving it upwardly countercurrent to the movement of the wood in order to effect prehydrolysis thereof, and withdrawing this water or solution from the digester at a point nearer the point of entry of the wood.
  • a continuous digester as shown in the Figure is operated with the addition at 11 of wood chips derived from eucalyptus at a rate equivalent to 210 lbs. oven-dry wood per minute, the addition at 12 of 30 gallons/minute of black liquor, and the addition at 13 of corrective alkali equivalent to 1 percent NaOH/ovendry wood.
  • white liquor is added at 16 at a rate equivalent to the addition of 17 percent NaOl-l/o.d. wood, i.e., 35.7 lbs. NaOH/minute at the heating circulation, and the equivalent of 1 percent NaOH/minute is added with the black liquor, i.e., 2.1 lbs. NaOH/minute.
  • the black liquor being discharged from the digester at contains 17 g.p.l. apparent active alkali when determined by potentiometric titration with hydrochloric acid to pH 8.0.
  • the rate of discharge of liquor at 15 in normal operation is 120 g.p.m.
  • the amount of corrective alkali being added to the black liquor at 13 was reduced by an amount equal to:
  • the method of this invention can be carried out by automation, for example in the following manner.
  • the black liquor being discharged at 15 is continuously sampled through a cooled sampling tube 21 so that it issues without flashing.
  • a sample of the stream is taken and by means of an automatic titrimeter 22 the apparent alkali content of the black liquor is determined as frequently as necessary, e.g., every 5 minutes.
  • the results of the apparent alkali content determinations are transmitted throu connection 21a to a computer memory 23 where the resu ts are stored and by means of a computer 24 (connected to the computer memory 23 by connection 23a) a running average of such determinations is compiled, taking in for example the current and previous live results.
  • a flow meter 25 measures the flow of black liquor from outlet 15 and a signal from this is also transmitted through connection 24a to the computer 24.
  • the product of the flow and apparent alkali concentration of the black liquor being discharged at 15 is calculated by the computer 24 and by means of a suitable program in the computer 24 the change in the position of valve 26 which is required to maintain the said product at a value preset for the operation, is calculated by the computer 24.
  • the required change in the position of the valve 26 is transmitted through connection 24b to the controller 27 which effects the required operation of the valve 26 through connection 270.
  • a suitable time delay is incorporated in the control circuit to allow for a predetermined delay between the time of changing the valve 26 and the time at which the corrected black liquor reaches the sampling point 21, so that hunting in the system is avoided.
  • the quantity of active chemical in the said further portion referred to in (c) being not greater than 20 percent of the total active chemical added to the digester

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US74513A 1966-06-24 1970-09-22 Countercurrent pulping of cellulosic materials including regulation of active chemical therein Expired - Lifetime US3652384A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AU7439/66A AU295860B2 (en) 1966-06-04 Improvements in the countercurrent pulping of cellulosic materials

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US3652384A true US3652384A (en) 1972-03-28

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US (1) US3652384A (no)
BR (1) BR6790820D0 (no)
DE (1) DE1692826A1 (no)
ES (1) ES342299A1 (no)
NO (1) NO122466B (no)
SE (1) SE346131B (no)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3941649A (en) * 1972-07-14 1976-03-02 Mo Och Domsjo Aktiebolag Process for obtaining a predetermined Kappa number in sulfate pulping
US4071399A (en) * 1976-09-01 1978-01-31 Kamyr, Inc. Apparatus and method for the displacement impregnation of cellulosic chips material
US4764251A (en) * 1983-11-30 1988-08-16 Ekono Oy Method for the impregnation and cooking of lignocellulosic material by a batch cooking using spent impregnation liquor from a previous batch
US5080755A (en) * 1988-12-20 1992-01-14 Kamyr Ab Process for the continuous digestion of cellulosic fiber material
US5089086A (en) * 1989-04-27 1992-02-18 Jaakko Poyry Oy Process for continuous cooking of cellulose
US5192396A (en) * 1988-12-20 1993-03-09 Kamyr Ab Process for the continuous digestion of cellulosic fiber material
US5207870A (en) * 1988-02-08 1993-05-04 Osmo Aho Process and equipment for pretreatment of cellulosic raw material
US5650045A (en) * 1994-12-14 1997-07-22 Salminen; Reijo K. Apparatus and method for wood pulp digester
US20020129911A1 (en) * 2000-10-16 2002-09-19 Marcoccia Bruno S. Process and configuration for providing external upflow/internal downflow in a continuous digester
US6789285B1 (en) * 1999-07-21 2004-09-14 Metso Paper Pori Oy Pulp washing method and plant

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2466290A (en) * 1944-03-15 1949-04-05 Paper Chemistry Inst Method of digesting pulp by the alkaline process
US2671727A (en) * 1948-05-05 1954-03-09 West Virginia Pulp & Paper Co Manufacture of pulp by the alkaline process
US3200032A (en) * 1961-12-23 1965-08-10 Kamyr Ab Continuous process for digesting cellulosic material
US3243341A (en) * 1961-11-20 1966-03-29 Improved Machinery Inc Continuous pulping apparatus
US3465550A (en) * 1965-12-03 1969-09-09 Systematix Chromatic control of bleaching process

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2466290A (en) * 1944-03-15 1949-04-05 Paper Chemistry Inst Method of digesting pulp by the alkaline process
US2671727A (en) * 1948-05-05 1954-03-09 West Virginia Pulp & Paper Co Manufacture of pulp by the alkaline process
US3243341A (en) * 1961-11-20 1966-03-29 Improved Machinery Inc Continuous pulping apparatus
US3200032A (en) * 1961-12-23 1965-08-10 Kamyr Ab Continuous process for digesting cellulosic material
US3465550A (en) * 1965-12-03 1969-09-09 Systematix Chromatic control of bleaching process

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3941649A (en) * 1972-07-14 1976-03-02 Mo Och Domsjo Aktiebolag Process for obtaining a predetermined Kappa number in sulfate pulping
US4071399A (en) * 1976-09-01 1978-01-31 Kamyr, Inc. Apparatus and method for the displacement impregnation of cellulosic chips material
US4764251A (en) * 1983-11-30 1988-08-16 Ekono Oy Method for the impregnation and cooking of lignocellulosic material by a batch cooking using spent impregnation liquor from a previous batch
US5207870A (en) * 1988-02-08 1993-05-04 Osmo Aho Process and equipment for pretreatment of cellulosic raw material
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
US5089086A (en) * 1989-04-27 1992-02-18 Jaakko Poyry Oy Process for continuous cooking of cellulose
US5650045A (en) * 1994-12-14 1997-07-22 Salminen; Reijo K. Apparatus and method for wood pulp digester
US6789285B1 (en) * 1999-07-21 2004-09-14 Metso Paper Pori Oy Pulp washing method and plant
US20020129911A1 (en) * 2000-10-16 2002-09-19 Marcoccia Bruno S. Process and configuration for providing external upflow/internal downflow in a continuous digester

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Publication number Publication date
BR6790820D0 (pt) 1973-05-15
NO122466B (no) 1971-06-28
SE346131B (no) 1972-06-26
ES342299A1 (es) 1968-07-16
DE1692826A1 (de) 1971-10-21

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