US2640774A - Production of cellulose pulp - Google Patents

Production of cellulose pulp Download PDF

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US2640774A
US2640774A US105162A US10516249A US2640774A US 2640774 A US2640774 A US 2640774A US 105162 A US105162 A US 105162A US 10516249 A US10516249 A US 10516249A US 2640774 A US2640774 A US 2640774A
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steam
pressure
plant material
chips
digester
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Ross James Hamilton
Hart John Semple
Strapp Richard Kevin
Maass Otto
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PULP AND PAPEN RES INST OF CAN
PULP AND PAPEN RESEARCH INSTITUTE OF CANADA
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PULP AND PAPEN RES INST OF CAN
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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
    • D21C1/00—Pretreatment of the finely-divided materials before digesting
    • D21C1/02—Pretreatment of the finely-divided materials before digesting with water or steam
    • 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
    • D21C1/00—Pretreatment of the finely-divided materials before digesting
    • D21C1/10—Physical methods for facilitating impregnation

Definitions

  • This invention relates to the production of cellulosepulp from plant materials
  • the estimation inthe pretreatmentiproceduret may bea; relatives point may be defined as that. state: in which: the 'iylow superatmospheric pressure. anda there is cavity" of the fibre is entirely free from: liquid nonecessityof-maintainingthe: maximiun steam moisture and its well is saturated? throughout; pressure for any appreciable period following It i sat this saturation-r point that a1 wo'ocl fibre 49 attainment tl'iereofi commences to shrink on drying and exhibits its practice ithas been found.
  • the steam pressure he maintained at this upper limit only momentarily in order to reduce to a minimum adverse effects of this high pressure steaming on the structure of the cellulose in the Wood and on the solubility of the lignin and other .binding substances in normal pulping liquors.
  • the lower limit to which the pressure in the pressure vessel is reduced during pretreatment of-the chips may be any pressure which can conveniently be arrived at within an allotted period of time suitable for economical commercial operation and which will give the required differential between the upper and lower limits of pressure. At this point, it may be noted that the efficiency of the pretreatment procedure increases with an increase in the rate at which the pressure is dropped from the upper to the lower limit.
  • the lower limit of pressure may be superatmospheric, zero or subatmospheric.
  • the mechanism of the pretreatment procedure may be explained as follows: During filling of the pressure vessel with steam to establish therein the selected upper limit of steam pressure and temperature, the wood chips are heated to the temperature of the surrounding steam which penetrates the chips to some extent. During the ensuing rapid reduction of the steam pressure to the selected lower limit, the water within the wood chips is flashed into steam and flows out of the chips with considerable velocity. This high velocity outflow of steam from within the wood chips serves to efiiciently purge the latter of air, free water and certain penetration-retarding solids which are entrained and removed by the outflowing steam.
  • the pretreatment procedure has the peculiar characteristic that it results in the moisture content of the chips being brought to or very close to the fibre saturation point by either increasing or decreasing the original moisture content of the chips.
  • the pretreatment adds the required amount of moisture in the form of absorbed water.
  • the pretreatment brings the moisture content close to the fibre saturation point by removing free water.
  • Repetition of the pretreatment proceedur is desirable and, in many cases, necessary to bring the moisture content of the pretreated chips sufiiciently close to the fibre saturation point and to efiect substantially complete purging of the chips of air, free water, and certain other penetration-retarding substances.
  • a single application of the pretreatment procedure may give commercially satisfactory results but, as a general rule, two or more applications of the pretreatment procedure will be found necessary to obtain the optimum results.
  • excessive repetition of the pretreatment procedure may have detrimental effects on the cellulose and should be avoided.
  • the predetermined procedure which constitutes the basic novel feature of the invention serves, by its unique moisture-content regulating efiect and its eflicient removal of penetration-retarding substances, to place the chips in the optimum condition for rapidly absorbing and uniformly distributing throughout their structure or tissue the defibrating reagents contained in the cooking or pulping liquor. It is also important to note that these results are obtained without in any way adversely affecting the pulp making qualities of the chips.
  • the wood chips After being pretreated in accordance with the present invention the wood chips are rapidly and uniformly impregnated with the cooking liquor and heated to a pulping reaction temperature by one of several alternative procedures, the selection of which is dependent on such factors as the nature or species of the pretreated chips, the kind of pulp desired, and the type of cooking liquor used.
  • Figure l is a graph showing the moisture content regulating effect of a typical pretreatment procedure to which the raw material is subjected in accordance with the invention prior to being impregnated with the cooking liquor and heated to a pulping reaction temperature;
  • Fig. 2 is a sectional View of a typical digester or pressure vessel which may be employed in the commercial application of the invention.
  • the graph (Fig. 1) shows the moisture regulating efiect obtained in a laboratory experiment by subjecting Douglas fir chips of widely varying original moisture content to four successive applications of the pretreatment purging procedure.
  • each: application or the: pretreatment procedure the: cycle: of: raising the: stem pressure the pressurevessel'. to: the? upper. limit ('40 lbs. per square inch): andi quickly reducing: it: to therlowerf limit lbs; pensduarez inch; was' com:- pleted; in: approxi'matelv three minutess. It will be: HOtBdz that this-2 pretreatment incneasedl the moisture: contents oi. chips: having; an; content? of from; 0% to 25%; and. reduced to 401% the moisture: content of: chips; having.
  • pretreats mentprocedure With. reference to repetitionof. the pretreats mentprocedure, it-has-also been. established; that wood with. moisture contents normally en:- countered as well. aswater soaked: woods. may be efiiciently: purged. of penetration-retarding; substances and. brought to a. uniform; moisture: cone tent closely approaching, the fibre saturation point-by: from .twoto -four. applications of the pretreatment procedure.
  • valves.- l 4, and. t6) are closed and. cooking; liquor: is introduced intothe. digester through aevalve. 2D to commence( the impregnation and pulping-re? action. stages of the complete processfor: the productiozn of. cellulose pulp;
  • the impregnation andi pulping of. the wood chips may be carriedoutasa single-stage operation in which impregnation-takes placewhile thacooking liquor in. the digester. isbeine gradually heated: up to attain. pulpingereaction temperatures: and pressures; Im this. case;, the pretreatment of the: chips ensures that, ..bw'the. time pulping: reaction conditions are obtained in the digester,, the; chips; will. be unitormly penetrated by the pulping; or chemicalareagentsiof the'cools ing liquor. to-a much greater degree thamheretoforelw-iththe result thatzthe pulp produced will be: of. a.
  • the impregnation and pulping of the chips may also be carried out in such manner as to constitute essentially a two-stage operation. Precautions are taken to maintain the temperature of the cooking liquor below the pulping-reaction temperature until it has been .determined that the chips have absorbed and uniformly distributed throughout their structure the full amount of defibrating chemicals of the cooking liquor which the chips are capable of absorbing and distributing throughout their structure. The contents of the digester are then heated up to attain pulping reaction conditions of temperature and pressure. This two-stage procedure gives a greater margin of safety with reference to ensuring that all the chips are uniformly impregnated to the fullest possible extent before being subjected to pulping-reaction conditions of temperature and pressure.
  • the partially exhausted liquor which is withdrawn from the digester when the chips are completely impregnated is fortified and brought back to its original strength by the addition of white liquor.
  • Part of the cooking liquor is then preferably withdrawn from the digester through the bottom strainer 15 and valve I6 before heating up the contents of the digester to attain pulping reaction temperatures and pressures.
  • the volume of liquor withdrawn from the digester following the impregnation of the chips maybe any desired proportion of the total volume of liquor introduced into the digester.
  • the chips since the chips have been fully impregnated, there is no necessity for retaining a large volume of excess liquor in the digester during the heating of the digester content to pulping reaction temperatures and considerable time and heat may therefore be saved by withdrawing from the digester, following impregnation of the chips, all but a very small amount of the excess liquor.
  • the small amount of excess liquor retained in the digester is substantially uniformly distributed among the chips during the actual cooking operation by steam distribution and by conventional liquor ciroulating methods.
  • the pressure employed in the pressure impregnation of the chips may be varied within wide limits ranging, for example, from about 20 lbs. per square inch to lbs. per square inch or higher. In a number of instances the chips were impregnated at a pressure of 100 lbs. per square inch and results were entirely satisfactory. However, in other instances, commercially satisfactory results were also obtained by impregnating the chips at an impregnating pressure of 20 lbs. per square inch. So far as can be determined from the results of numerous experimental and commercial applications of the invention, there appears to be no particular advantage in using impregnating pressures above 100 lbs. per square inch but it is possible that extended applications of the invention may disclose instances in which use of higher pressures may develop some advantages.
  • the ratio of the strength of the partially exhausted liquor withdrawn from the digester upon completion of impregnation appears to vary according to the original strength of the liquor and the temperature at which the impregnation takes place and this consideration should be borne in mind in determining the strength of the original cooking liquor.
  • Another advantage of the present invention is that it lends itself to the uniform pulping of a mixture of woods of different species which cannot be uniformly pulped by conventional pulping procedures. By carrying out the pretreatment, impregnation and pulping reaction procedures as prescribed by this invention, it has been found possible to produce a uniform pulp of commercially satisfactory quality from a mixture of jack pine and poplar wood chips mixed together in equal proportion by Weight.
  • valves 14 and I6 were immediately opened to reduce the steam pressure in the digester to 10 lbs. per sq. in. as rapidly as possible. This reduction of steam pressure required approximately 6 minutes.
  • the valves M and I6 were closed and steam valve 8 again opened to again raise the steam pressure in the digester to 20 lbs. per sq. in. This second raising of the steam pressure to the specified upper limit reace-emu 9 uu-ired approximately minutes.
  • the cooking liquor used was a regular hra-ft cooking liquor of approximately 30% *stilphidity .and cont lug approximately .l'6f5'% active alkali.
  • a sufilcient amount oi the surplus cooking liquor was then immediately withdrawniromthe ldigester to reduce the liquor to wood ratio to about 2.3 to 1, calculated on the basis of the bone dry weight of the wood.
  • the contents of the digester were ⁇ thenheateiil to Ctin lfiminutes and this temperature was maintained for hours. This operation produced a total yield 53.2% of good quality uniformly cooked pulpwtdth a screen yield of approximately 53%.
  • the pulp was QUi'bBBOft with no evidence of burning.
  • the chips had taken up the maximum amoimt of acid which they were capable of absorbing and side relief of "the di- "gester was resorted to fora period'of -15 minutes.
  • fl he temperature of the digester contents was thenraised tOfiPDlOXllll-EISGIY Mo -C. the shortest possible time that the system would permit by -introduction :of steam. This required about 21 05 ;minutes:and the temperature was'maintained cat-the :level of i '6. :for ':a further period "of '20 minutes. A further period of 30 minutes was used up in reducing the pressure in the digester.
  • the digester used in Example III was a conventional sulphite digester of approximately ten tons accepted pulp capacity and was provided with a conventional hot acid cooking system. With a digester of this type the normal time required for completion of a cock, as measured from the commencement of steaming until the blowdown, was 7 hours.
  • each chip is, in fact. its own digester.
  • the species more easily pulped does not have access, after delignification, to a continuing supply of chemical. and so further degrading of the pulp does not take place.
  • the result is, therefore, a uniform product from a mixture of species. It may be again emphasized that the conditioning of the chip to its constant moisture saturation value, coupled with its ability to subsequently receive an adequate amount of chemical in solution is an essential feature of this process.
  • the process which consists of the steps of introducing plant material in subdivided condition into a pressure vessel; displacing air in said pressure vessel with steam; subjecting said plant material within said pressure vessel to a pre-treating operation which comprises introducing steam under pressure to establish within the capilliary interstices of the plant material a mixture of air and steam until a pressure of from about five to about fifty pounds per square inch gage pressure is reached, then discontinuing the introduction of steam, and while excluding additional air from said pressure vessel forthwith rapidly withdrawing said mixture of air and steam from said pressure vessel and from the interstices of said plant material until a pressure is reached within the range of from atmospheric pressure to a gage pressure half that which existed when the introduction of steam was discontinued; thereafter immersing said pro-treated plant material in cooking liquor while continuing to exclude air from said plant material, the quantity of cooking liquor being sufiicient to completely submerge said pre-treated plant material; withdrawing a substantial portion of the cooking liquor surrounding said plant material; and then

Description

Patented June 2, 1953 ada, Montreal; Quebec, Canada-l Application .luiylfi, 1949, SerialNt'; 11152162 This invention relates to the production of cellulosepulp from plant materials The invention is herein desoribed as applied to the: chemical pulping of Wo'o'cl chips but the principles and procedures involved: are appliireduction at the steam pressure to; the lower cable,- in Whole in part, tothe pulping of limit to he: aeoomplished= inv as brief; period: of straw; bamboo and otherligno cellulosio matesial time sush for example, a e-51 or: 5: minutes. In by the sui'phate; sulphiteand other-knownohemie this pretreatment procedure the: optimum. re;- oai pulping processes; suits are attained by raisingz the; steam; pressure it salient feature of the invention: consists" in m to the upper limit as rapidiy as possible; con-.- che provision: ofapretre'atm'ent pi oeeduref where.- si'ste'ntwithuniform: heating oi the chips; to the by wood chips of widely varying: original: moisture temperature oi the surrounding steam: and; by content, preferably within the eommeroial range discontinuing the introduotioniofi stearm and-ink 25 to 50%: original moisture content, are ion the rapi'zl pressure reducing: withdrawal brought-to asubstantiallyuniform moisture con:- or steam from the vessel; soon; the upper tent, corresponding to or closely approaching? the limit of steam: pressure is attained; When; the fibre saturation: point for wood; and are otherraising" lowering ofi the steam pressure, is wise conditioned -to' facilitate the: rapid" uni? carried out in this preferredi manner, theztotal form penetration thereof by an aqueous solut-iine requiredfor the pretreatment procedure tionof defibra-tlng reagentsoom'moniy referred is-reduceol to aminimumiwhieh iszdesirable both to as the cooking liquor; In: an article published from the standpointof: economy Qfi opexzationand in Industrial and Engineering Chemistry; vol. reduction ofithe l'engthof: time: thEwWVQQdLChiQS 1, No; 2', Aprill5'; I929; L. Stains-m hasv pointed are exposed tothe acti'omofi thezsteam, theilatter out that the term fibre: saturation point! was consideration being important to ensure; oonrli; first used connection with wood to designate tioning of the chips for rapidi, and& uniform the moisture. content below which turthen reimpregnation thereof by defibrating reagents c'iuction of moisture: caused changes ing the with-theleast-possible: danger: of; impairing. the strength of 'thewood Inthissamearticle:Stamm paper making; properties. on. the chips. In: this also points out that the: absorption oi water by connection, t Sd p fi note that the; die;- woodbelongs to the same general class of sii'ed conditioningof the chips by the: pretreatr phenomena as the absorption ofi various: liquids ment procedureorftheipresentlinuentionis not do:-
diferent" fibIOllS- material. and; very closely pendent on the: use? as high: maximum-1 steam resembles the absorption or water by otheir celipressures or on: prolonged exposure; of; the wood luiosic fibres. Water" contained in wood; fibre ehips-to-theaetiom of! the, steam. On: the con,-
in two forms; i. 6;, free Water and absorbed trary', the maximum: steam; pressure; employed water anti, accordingi to: Stamm,. the estimation inthe pretreatmentiproceduretmay bea; relatives point may be defined as that. state: in which: the 'iylow superatmospheric pressure. anda there is cavity" of the fibre is entirely free from: liquid nonecessityof-maintainingthe: maximiun steam moisture and its well is saturated? throughout; pressure for any appreciable period following It i sat this saturation-r point that a1 wo'ocl fibre 49 attainment tl'iereofi commences to shrink on drying and exhibits its practice ithas been found. that:- there' is; a maximumability for alesorpti'on and;v diffusioni of wise-range: within which the values to which the deribrating reagents aqueous solution; steam-pressureandtemperature.aresraiseitclusln thepretieatnrentproeedure-aifordedbythe ing the pretreatment proeedurea be varied present invention the wood chips ofi varying depending on the nature. an'di condition ofi the original moisture content are brought. to': a sub- Wood andcompliance: with spieoifie: requirements stantially uniform moisture content; closely apconcerning yield: and quality" of; the: pulp; to; be preachingthe: fibre saturation poiht. by packing produced front the: pretreatedi chips; thechipsinto as. pressurevessel; introducing The important faotorsgoverning; thesei mi steam into the vesselto" expel air therefrom 50 of the upperand lower limits: or steam: pressure through suitable vent opening; closing the employed in the pretreatmentprooedulzeare time veritopening when the: vessei is oieared of air minimum: impairment of the: pulp? making and; continuing the introduction: of: steam until pronert'iesof the woods The: results on numerous the vessel isfill'ed with steam at aipreti'etermmed experimentsand sommerciai app'licationszofi the superatmospherio pressure; ant-1i their rapidly 1 3* 2 dosing-the steam pressureto a predetermined lower value by disoontinuing the supply: of" steam and venting the vessel through one on more steamoutlets" of sumcient capacity tot enaole invention indicate that use? of? maximum steam pressures substantially higher than 50 lbs. per square inch is not commercially economical because of the length of time required to attain such higher pressures in commercial digesters. Moreover, the us of such higher pressures prolongs the time of exposure of the wood chips to the steam and thereby increases the hazard of impairing the pulp making properties of the chips by hydrolysis, distillation and other adverse eifects of superatmospheric steam. Hence while usable pulp may be produced by pretreatment of the wood chips at maximum steam pressures exceeding 50 lbs. per sq. in., the operating time is not economical and the yield and quality of the pulp produced from the pretreated chips is inferior to that obtained from chips pretreated at maximum temperatures below or not exceeding 50 lbs. per sq. in. The optimum maximum pressure recommended for the pretreatment procedure is approximately 20 lbs. per sq. in. This pressure can be reached in a very few minutes in a commercial digester and if not maintained for an excessive period of time before being reduced to the lower limit, gives entirely satisfactory conditioning results with a wide margin of safety as regards avoidance of any appreciable impairment of the pulp making properties of the wood by the action of the steam. High maximum pretreatment pressures ranging from 20 lbs. to 50 lbs. per sq. in. have also been used in procedures which gave an increased yield of uniformly cooked good quality pulp representing a definite improvement over the yield and quality of pulp obtained by conventional pulping procedures not employing the pretreatment prescribed by the present invention. When pretreating wood chips at maximum pretreatment pressures of the order of 40 to 50 lbs. per sq. in. or higher, it is especially desirable that the steam pressure he maintained at this upper limit only momentarily in order to reduce to a minimum adverse effects of this high pressure steaming on the structure of the cellulose in the Wood and on the solubility of the lignin and other .binding substances in normal pulping liquors.
The lower limit to which the pressure in the pressure vessel is reduced during pretreatment of-the chips may be any pressure which can conveniently be arrived at within an allotted period of time suitable for economical commercial operation and which will give the required differential between the upper and lower limits of pressure. At this point, it may be noted that the efficiency of the pretreatment procedure increases with an increase in the rate at which the pressure is dropped from the upper to the lower limit. The lower limit of pressure may be superatmospheric, zero or subatmospheric.
The mechanism of the pretreatment procedure may be explained as follows: During filling of the pressure vessel with steam to establish therein the selected upper limit of steam pressure and temperature, the wood chips are heated to the temperature of the surrounding steam which penetrates the chips to some extent. During the ensuing rapid reduction of the steam pressure to the selected lower limit, the water within the wood chips is flashed into steam and flows out of the chips with considerable velocity. This high velocity outflow of steam from within the wood chips serves to efiiciently purge the latter of air, free water and certain penetration-retarding solids which are entrained and removed by the outflowing steam.
In addition to efliciently purging the wood chips of air, free water and other penetration retarding substances, the pretreatment procedure has the peculiar characteristic that it results in the moisture content of the chips being brought to or very close to the fibre saturation point by either increasing or decreasing the original moisture content of the chips. When the original moisture content of the chips is below the fibre saturation point the pretreatment adds the required amount of moisture in the form of absorbed water. When the original moisture content of the chips is above the fibre saturation point, the pretreatment brings the moisture content close to the fibre saturation point by removing free water.
Repetition of the pretreatment procedur is desirable and, in many cases, necessary to bring the moisture content of the pretreated chips sufiiciently close to the fibre saturation point and to efiect substantially complete purging of the chips of air, free water, and certain other penetration-retarding substances. Under especially favourable conditions a single application of the pretreatment procedure may give commercially satisfactory results but, as a general rule, two or more applications of the pretreatment procedure will be found necessary to obtain the optimum results. On the other hand excessive repetition of the pretreatment procedure may have detrimental effects on the cellulose and should be avoided.
From the foregoing discussion it will be seen that the predetermined procedure which constitutes the basic novel feature of the invention serves, by its unique moisture-content regulating efiect and its eflicient removal of penetration-retarding substances, to place the chips in the optimum condition for rapidly absorbing and uniformly distributing throughout their structure or tissue the defibrating reagents contained in the cooking or pulping liquor. It is also important to note that these results are obtained without in any way adversely affecting the pulp making qualities of the chips.
After being pretreated in accordance with the present invention the wood chips are rapidly and uniformly impregnated with the cooking liquor and heated to a pulping reaction temperature by one of several alternative procedures, the selection of which is dependent on such factors as the nature or species of the pretreated chips, the kind of pulp desired, and the type of cooking liquor used. These various impregnating and pulping procedures and the basis on which they are selected in accordance with the nature and condition of the raw material and the kind of pulp desired are hereinafter fully described with the aid of suitable examples and with reference to the accompanying drawings, in which:
Figure l is a graph showing the moisture content regulating effect of a typical pretreatment procedure to which the raw material is subjected in accordance with the invention prior to being impregnated with the cooking liquor and heated to a pulping reaction temperature; and
Fig. 2 is a sectional View of a typical digester or pressure vessel which may be employed in the commercial application of the invention.
The graph (Fig. 1) shows the moisture regulating efiect obtained in a laboratory experiment by subjecting Douglas fir chips of widely varying original moisture content to four successive applications of the pretreatment purging procedure.
each: application or the: pretreatment procedure the: cycle: of: raising the: stem pressure the pressurevessel'. to: the? upper. limit ('40 lbs. per square inch): andi quickly reducing: it: to therlowerf limit lbs; pensduarez inch; was' com:- pleted; in: approxi'matelv three minutess. It will be: HOtBdz that this-2 pretreatment incneasedl the moisture: contents oi. chips: having; an; content? of from; 0% to 25%; and. reduced to 401% the moisture: content of: chips; having. an;origi'nal moisture: content of approximately 551%.c It will alscr be: seem that in: the: very; extreme: case of chipshaving; am original: moisture content of 185%,, the-.- pretreatment. reduced the: moisture content to;54-%. The originalimoisure-content of wood. chips: originally employed. in; the. produc of cellulose: pulp lies within: the: range of 2 tor 55%- and-,.,in: this range;,the=pretnea;tment procedure is effective..- to: bring; alL the chips to a uniform. moisture content of: approximately 40 WhiGhi is; very close: to the fibre saturation point at. which; the chips exhibit their: maximum ability to: absorb: and. uniformls dis-tribute throughout theirstructure defibratin'g; reagents which are brought in contact.- witlr the: chips in aqueous solution.
Commercial. applications of; the invention have been carried outv in: a digester oi the type:- indicatedlat 5 inaFig. 2.. The? raw woodzchips-a-re introduced'. into the digesten throughi the'top filling opening.-v t-wi-thorwithout the: aid of conventional n" p in equipment. At same: time;, or at any other suitable time; steam-a is admitted: to the: bottom of. the: digester by;- steam supply line 1;, steami valve 8' and tha digester: blowdownoutlet-- 9? which controlled; by; an normally.- closed blowdown valve In... When-.thadigester has been suificientlyi packed chips; the filling opening 6 is closed by a cover ll: andithaintroduetion of steam is continued until the air in the digester has been expelled through a strainer 12, a vent passage I3 and an open vent valve l4 provided at thetop ofithedigesten. Whenall the air. hasbeen expelled. from the digester,. steam is discharged throughventivalve Ill whichislthen closed and steaming continued to attain, as quickly as. possible, the selected. upper limit. oi! steam. pressure and. temperature... The steam is then. immediately shut' off and. rapid. reduction ofthe. steam. pressure. tofithe lower limit is initiated. withtthe. least-possible delay byexhausting steamv from. the. digester through a bottom strainer. l 5and. a. drain valve [6 which controls a. drain conduit Ill communicating: with. a space It reserved betweenv strainer. 15. and. the: lower conicalbottom portion- 1.9 of. the digester. When drain valve 16.- is' opened, vent. valve. M is. also preferably opened. to facilitate the. desired rapid reduction of the steam pressure: within the disesten.
It: is important; that the? digester: have adequate provision. forv rapid. reductiorr. in steamv pressure: Manydigesters now: in: use. do nothave adequate provision-.ror this purpose; and: if itis'. desiredto practicethe-present:inventiorrin suclrdigesters it is; recommended. that be? altered, preferably along; the lines of. the: digester." described. herein. Thus in. some. instances it; may benecessarv=- to installv a. strainer such. as: the bottom strainer 15,. and; a. drain valve: and conduit. of. large ca?- pacity such. assthe. valve. Ht andzthc. conduit l1 shown: inthedrawings.
lncasesswhere itLisinecessa-ry to: repeat thesprertreatment; procedure: to tiring; the: wood. chips: to the fibrersaturatiompoint and; to: efficiently purge 6i them of air, free water am other penetration-retarding substances the expulsion of; air: and: the; heating: ofi the chips during: the initial. application. of; the pretreatment procedure enables. the: desired raising and lowering"; ofa steamipressure inisucceeding: applicatinnssof: such procedure: to be appreciably shortened; as: com;- pared'. with the.- time required by the initial; prertreatment of. the chips.
The steam. which: discharged: through tent valve? Ht, during the chipiheating; andiair-exp'eiling stage; of; the: pre'treatmentiprocedure at a: tentperature of; approximatelwalz Theiintroducztion". of: steam: into." the digester followinggthe closure of vent valvei M discontinued as soon as the. desired upper limiter; steamipressura and temperature: isneachedi. and this upper: limit should; notexceed; a steam; pressure; or. 405' lbsz. per square inch-z witlr a corresponding; temperature: of C; and: should: not beheld atthis: upper limit. for any-P appreciable length of. time: suificient to impair. the: paper-making qualities: of the pretmaat'ed': chips;
While: the upper. and; lower limitsiofi steam pressure employed: in the: pretreatment procedure be widely variedawithini therprescribedrange; the selection; of. theselimits': and. the extent, if any, to which the pretreatment procedureai'stresa posted, will obviously be: based: cm the.- attainment of commercially satisfactory results in: the
shortest: possible. time; having; regard-to the nae ture-arreLcondition of.- the=ravw material; Various trials. have established the fact. that, in. a large number of cases, commercially? satisfactory results can be obtained, in the pretreatment of: the
chips, by varying the steam: pressure: from; an
upper. limit of. 2G lbseper, err. in. to a lower. limit of. 10 lbs; per sqt in.
With. reference to repetitionof. the pretreats mentprocedure, it-has-also been. established; that wood with. moisture contents normally en:- countered as well. aswater soaked: woods. may be efiiciently: purged. of penetration-retarding; substances and. brought to a. uniform; moisture: cone tent closely approaching, the fibre saturation point-by: from .twoto -four. applications of the pretreatment procedure.
When thepretreatment procedure is completed valves.- l 4, and. t6) are closed and. cooking; liquor: is introduced intothe. digester through aevalve. 2D to commence( the impregnation and pulping-re? action. stages of the complete processfor: the productiozn of. cellulose pulp;
The impregnation andi pulping of. the wood chips may be carriedoutasa single-stage operation in which impregnation-takes placewhile thacooking liquor in. the digester. isbeine gradually heated: up to attain. pulpingereaction temperatures: and pressures; Im this. case;, the pretreatment of the: chips ensures that, ..bw'the. time pulping: reaction conditions are obtained in the digester,, the; chips; will. be unitormly penetrated by the pulping; or chemicalareagentsiof the'cools ing liquor. to-a much greater degree thamheretoforelw-iththe result thatzthe pulp produced will be: of. a. more uniform; character in thatit will contain smaller: percentages: of overcooked: and undercooked fibres.- 'lihe: rapidity and. deg-rem of uniliormitw with: which the. pretreated. chips: are impregnated also. oifers the. possibility of. sately shortening: the cooking; cycle: by,- increasingethe rapidity" with which the: cooking liquor is: heated up to: aapulping; reaction. temperature; and' detcreasing; tha length. of time. during" which the chips are left in contact with the: c'ock-ingiliquon after pulping-reaction conditions have been attained.
The impregnation and pulping of the chips may also be carried out in such manner as to constitute essentially a two-stage operation. Precautions are taken to maintain the temperature of the cooking liquor below the pulping-reaction temperature until it has been .determined that the chips have absorbed and uniformly distributed throughout their structure the full amount of defibrating chemicals of the cooking liquor which the chips are capable of absorbing and distributing throughout their structure. The contents of the digester are then heated up to attain pulping reaction conditions of temperature and pressure. This two-stage procedure gives a greater margin of safety with reference to ensuring that all the chips are uniformly impregnated to the fullest possible extent before being subjected to pulping-reaction conditions of temperature and pressure. It also lends itself to withdrawal of a substantial proportion of the cooking liquor following complete impregnation of the chips and thus enables the heating of the contents of the digester to attain pulping reaction conditions to be carried out with greater rapidity, thus contributing to the saving of both heat and time.
When the impregnation and pulping of the chips is carried out as a two-stage process, as
above described, the partially exhausted liquor which is withdrawn from the digester when the chips are completely impregnated is fortified and brought back to its original strength by the addition of white liquor.
When impregnation and pulping of the chips is carried out as a two-stage process, it has been found that pressure impregnation of the chips serves, in conjunction with the pretreatment procedure, to provide the optimum conditions for the most complete and uniform impregnation of the chips in the shortest possible time preceding heating of the impregnated chips to pulping reaction temperatures. When pressure impregnation is resorted to, the cooking liquor is pumped into the digester through valve 20 and is placed under the required pressure either by means of the liquor pump or by injecting steam into the top of the digester in any suitable manner and preferably through the top strainer l2. pressure on the cooking liquor is maintained for a suitable period of time to ensure the best pos sible penetration results. Part of the cooking liquor is then preferably withdrawn from the digester through the bottom strainer 15 and valve I6 before heating up the contents of the digester to attain pulping reaction temperatures and pressures. The volume of liquor withdrawn from the digester following the impregnation of the chips maybe any desired proportion of the total volume of liquor introduced into the digester. In this connection, it may be noted that since the chips have been fully impregnated, there is no necessity for retaining a large volume of excess liquor in the digester during the heating of the digester content to pulping reaction temperatures and considerable time and heat may therefore be saved by withdrawing from the digester, following impregnation of the chips, all but a very small amount of the excess liquor. The small amount of excess liquor retained in the digester is substantially uniformly distributed among the chips during the actual cooking operation by steam distribution and by conventional liquor ciroulating methods.
The
The pressure employed in the pressure impregnation of the chips may be varied Within wide limits ranging, for example, from about 20 lbs. per square inch to lbs. per square inch or higher. In a number of instances the chips were impregnated at a pressure of 100 lbs. per square inch and results were entirely satisfactory. However, in other instances, commercially satisfactory results were also obtained by impregnating the chips at an impregnating pressure of 20 lbs. per square inch. So far as can be determined from the results of numerous experimental and commercial applications of the invention, there appears to be no particular advantage in using impregnating pressures above 100 lbs. per square inch but it is possible that extended applications of the invention may disclose instances in which use of higher pressures may develop some advantages. The ratio of the strength of the partially exhausted liquor withdrawn from the digester upon completion of impregnation appears to vary according to the original strength of the liquor and the temperature at which the impregnation takes place and this consideration should be borne in mind in determining the strength of the original cooking liquor. Another advantage of the present invention is that it lends itself to the uniform pulping of a mixture of woods of different species which cannot be uniformly pulped by conventional pulping procedures. By carrying out the pretreatment, impregnation and pulping reaction procedures as prescribed by this invention, it has been found possible to produce a uniform pulp of commercially satisfactory quality from a mixture of jack pine and poplar wood chips mixed together in equal proportion by Weight.
The invention is further illustrated by the following examples:
EXAMPLE 1'.
Production of Icraft pulp from jack pine chips having an original moisture content within the normal commercial range The chips were packed into the digester through opening 6 by a conventional steam packer (not shown), aided by introduction of steam into the bottom of the digester through steam valve 8. q The introduction of steam into the bottom. of the digester through valve 8 was effected at the maximum rate consistent with prevention of the steam breaking through the chip charge. When the digester was sufficiently packed with chips, the charging opening 6 was closed by cover H with vent valve l4 open. The supply of steam through valve 8 was continued until a steam discharge temperature of 212 F. was registered at vent valve Hi. The valve 64 was then closed and the introduction of steam through valve 8 continued until the steam pressure in the digester was raised to 20 lbs. per sq. in. This required approximately '7 minutes. The supply of steam through valve 8 was then immediately discontinued and valves 14 and I6 were immediately opened to reduce the steam pressure in the digester to 10 lbs. per sq. in. as rapidly as possible. This reduction of steam pressure required approximately 6 minutes. When the lower limit of pressure was reached, the valves M and I6 were closed and steam valve 8 again opened to again raise the steam pressure in the digester to 20 lbs. per sq. in. This second raising of the steam pressure to the specified upper limit reace-emu 9 uu-ired approximately minutes. The valve 2E5 was then immediately reclosed and the relief valves M and B "quickly open-ed to again reduce the steam pressure in the digester to I=1'-0 lbs. .per
sq. This secondreduotionloi thesteamapres -5 sure to the lower limit required. about minutes. In this case no further repetition of "the pretreatmehtproeed-ure was iound'nccessary toibring the chips to the fibre saturation :point sand 'Ebf) e'fiec't a satisfactory purging of the :c'hips of :air, free water and other "penetration-resisting zsubstances.
When the pretreatment prooedure was roompleted, the cooking liquor mrrlpecl :into the ,digester "to "completely fill the same and the liquor pump was continued in operation tor a. iiurther :period of two to three minutes. At the rendof this time, the level *record'er ion the liquor :tan'k showed :no fu'rther decrease volume ar-1d the liquor supply pump was shut :oii'.
Following *the shutting 0ff of .ithe liquor supply pump, the cooking liquor in the digester wassub iiected'to mechanical pressure by *means of steam introduced "into the top of the :digester.
pressure applyin steam actedas-aipistomon top the digester and returning it "to the iliquor tan l;
at the end of the pressure impregnation lot the chips. 'The'tota-l period -o'f timere'quired'for filling the digester with the -codking jiiquor and eflecting the pressure impregnation of :the rchips was approximately 12 minutes and the temperature of impregnation was helow the pulpingreaction'temperature. 7
When the cooking liquor "in the digester was -reduced to the selected level, following completion oi the pressure impregnation of rthe ohips, l
steam was introduced into the :diges'ter to bring the contents thereof to a maximum temperature of approximatelyfifiil" F. l his requiredlappmxi- -mately minutes and the pulping readtion' temperature thus established was maintained for a further period of approximately 'two hours to complete "the cook.
"The cooking liquor used was a regular hra-ft cooking liquor of approximately 30% *stilphidity .and cont lug approximately .l'6f5'% active alkali.
This operation produced a good quality of .un'i- Jformly cooked pulp with an increased .yield of ,irom 2% .to 3.2%.. The pulp .was easily washed with less Water than is usuallylrequired .and conztaineda reduced amount of .lsnotter rejects. The steam consumption and the timerequiredtocompiste the cook -was vappremlab-ly reduced rclue to the llow ratio -.of cooking diquor to wood :employed in the zdeiibrating reaction stage 'of theprocess. "slhegpretreatment 'of chips, plus the :low "liquor no mood ratio employed in the ideiibrating :reaction stage enabled the temperature of thesiig-ester "contents to he :raised ito the pulping reaction temperature *as rapidly as the system would rper- --mit this "makes it possible to 'mcrease the digester turnover, that is to say, in themun-rber of cooks 'coulp'let'edin 'eachiiigester over a period of such as '24 hours.
.i'I Production .0; Suzann ,puzzp with low liquor to wood ratio during the defibrating reaction stage of the process The chips were packed into disaster {and were subjected to iour applications of the pretreatment procedure carried out :as described in Example I "The digesterwas then filled XVI-171178711 amount of sulphite cooking :liquor :swiieient to :completely submerge the chips and the fliquor was then subjected, 'for rs. "period "of ten :minutes, to aprcssureaof ioiirlbsxfper square'inch at afternperature below the deiibrating reaction temperature. A sufilcient amount oi the surplus cooking liquor was then immediately withdrawniromthe ldigester to reduce the liquor to wood ratio to about 2.3 to 1, calculated on the basis of the bone dry weight of the wood. The contents of the digester were {thenheateiil to Ctin lfiminutes and this temperature was maintained for hours. This operation produced a total yield 53.2% of good quality uniformly cooked pulpwtdth a screen yield of approximately 53%. The pulp was QUi'bBBOft with no evidence of burning.
. EXAMPLE III Production of ,sulphite pulp from western hemlock phi-p3 In this case the-digester was packed with Wood .chipsiin thelsame manner as described mammp'le 'I ,'namel y,, with-the aid of a chippackerand the admission of steam to theihottom of the .digester through the steam valve "3. This required aperiod of,approximatelyjfiolininutes.
"When packing of the disaster with chips was completed, the charging opening (6 WaSlChSCl cover H; vent valve M was opened; and the introduction .o'f steam was continued .throu h valve I8 untilsteam was discharged thrcugh vent valve M at .a temperature 212 F. .This .required a period voi approximately '8 minutes.
.As .soon as the .temperature of the steam .discharged through vent valve 1 1 was .registeredat 21'2F., the valve M wasclosedandtheintroduc tion of steam through valve 8 continued until the steampressurein the digester rcgisteredfi lbs. per sq. m. This required filproximately 1.0 minutes. The-introduction ofsteam into the .digester was then discontinued and the steam pressure in the 'diges'ter reduced as rapidly aspossible t0.3 ,per sq. in. by withdrawing steam therefrom. aghis reduction of pressure required approximately 5 minutes and the pretreatment procedure was not repeated.
Following the reduction of steam pressure .in the digesterto 3 "l'hs'per'sq. in. at the endof the pretreatment procedure, 'cookingacid'irom acuit- --able accumulator was pumped into the digester and the acid supply pump was continued in .operation-un'tilthe level'in the -accuxmilator had ceased to fall. Thepump pressure thus'establishedinthe 'digester after the latter was filled with 'acidwas approximately 75' lbsk per "sq. in. and was "arrived --at in an acid charging period of approximately 30 minutes. By this time, the chips had taken up the maximum amoimt of acid which they were capable of absorbing and side relief of "the di- "gester was resorted to fora period'of -15 minutes. fl he temperature of the digester contents was thenraised tOfiPDlOXllll-EISGIY Mo -C. the shortest possible time that the system would permit by -introduction :of steam. This required about 21 05 ;minutes:and the temperature was'maintained cat-the :level of i '6. :for ':a further period "of '20 minutes. A further period of 30 minutes was used up in reducing the pressure in the digester.
The digester used in Example III was a conventional sulphite digester of approximately ten tons accepted pulp capacity and was provided with a conventional hot acid cooking system. With a digester of this type the normal time required for completion of a cock, as measured from the commencement of steaming until the blowdown, was 7 hours.
The yield and quality of pulp produced by this operation was substantially the same as that obtained by the procedure described in Example II.
EXAMPLE IV Production of uniformly cooked kraft pulp from jack pine and poplar wood chips mixed together in equal proportions In this case the procedure followed, except as regards the use of a mixture of wood chips of different species, was exactly as described in Example I.
In the pulping of mixed species of wood in accordance with the procedure prescribed in Ex-- ample IV, it appears that the uniform pulping results obtained are due to the fact that each chip is made to take up a miximum amount of liquid which is constant or approximately so for each species.
be made sufficient for the pulping reaction and therefore each chip is, in fact. its own digester. Thus the species more easily pulped does not have access, after delignification, to a continuing supply of chemical. and so further degrading of the pulp does not take place. The result is, therefore, a uniform product from a mixture of species. It may be again emphasized that the conditioning of the chip to its constant moisture saturation value, coupled with its ability to subsequently receive an adequate amount of chemical in solution is an essential feature of this process.
This operation produced a good quality or uniformly cooked pulp of mixed species with the increased yield and other advantages pointed out in connection with Example I. The poplar was not overcooked and the rejects were normal.
Having thus described the principles of our invention and several applications thereof, it will be understood that various modifications may be resorted to within the scope and spirit of the invention as defined by the appended claims.
We claim:
1. In the production of cellulose pulp from fibrous plant material, the process which consists of the steps or introducing plant material in subdivided condition into a pressure vessel; displacing air in said pressure vessel with steam; subjecting said plant material within said pressure vessel to a pro-treating operation which compries introducing steam under pressure to establish within the capillary interstices of the plant material a mixture of air and steam until a pressure of from about five to about fifty pounds per square inch gage pressure is reached, then discontinuing the introduction of steam, and while excluding additional air from said pressure vessel forthwith rapidly withdrawing said mixture of air and steam from said pressure vessel and from the interstices of said plant material until a pressure is reached within the range of from atmospheric pressure to a gage pressure half that which existed when the introduction or" steam was discontinued; thereafter immersing said pro-treated plant material in cooking liquor whilecontinuing The amount of chemical taken up, by I regulating the concentration of the solution, can
12 to exclude air from said plant material; and then cooking said pre-treated plant material.
2. The process of claim 1 in which the pretreating operation is carried out a plurality of times before the plant material is immersed in cooking liquor.
3. In the production of cellulose pulp from fibrous plant material, the process which consists of the steps of introducing plant material in subdivided condition into a pressure vessel; displacing air in said pressure vessel with steam; subjecting said plant material within said pressure vessel to a pre-treating operation which comprises introducing steam under pressure to establish Within the capillary interstices of the plant material a mixture of air and steam until a pressure of from about five to about fifty pounds per square inch gage pressure is reached, then discontinuing the introduction of steam, and while excluding additional air from said pressure vessel forthwith rapidly withdrawing said mixture of air and steam from said pressure vessel and from the interstices of said plant material until a pressure is reached within the range of from atmospheric pressure to a gage pressure half that which existed when the introduction of steam was discontinued; thereafter immersing said pretreated plant material in cooking liquor at a temperature below that of defibration reaction While continuing to exclude air from said plant material; subjecting said plant material and cooking liquor to a substantial hydrostatic pressure to force said cooking liquor into th interstices of said plant material; and then heating said impregnated plant material to defibration reaction temperature.
4. The process of claim 3 in which the pretreating operation is carried out a plurality of times before the plant material is immersed in cooking liquor.
5. In the production of cellulose pulp from fibrous plant material, the process which consists of the steps of introducing plant material in subdivided condition into a pressure vessel; displacing air in said pressure vessel with steam; subjecting said plant material within said pressure vessel to a pre-treating operation which comprises introducing steam under pressure to establish within the capilliary interstices of the plant material a mixture of air and steam until a pressure of from about five to about fifty pounds per square inch gage pressure is reached, then discontinuing the introduction of steam, and while excluding additional air from said pressure vessel forthwith rapidly withdrawing said mixture of air and steam from said pressure vessel and from the interstices of said plant material until a pressure is reached within the range of from atmospheric pressure to a gage pressure half that which existed when the introduction of steam was discontinued; thereafter immersing said pro-treated plant material in cooking liquor while continuing to exclude air from said plant material, the quantity of cooking liquor being sufiicient to completely submerge said pre-treated plant material; withdrawing a substantial portion of the cooking liquor surrounding said plant material; and then cooking said pre-treated plant material.
6. The process of claim 5 in which the pretreating operation is carried out a plurality of times before the plant material is immersed in cooking liquor.
'7. In the production of cellulose pulp from fibrous plant material, the process which consists of the steps of introducing plant material in subdivided condition into a pressure vessel; displacing air in said pressure vessel with steam; subjecting said plant material Within said pressure vessel to a pre-treating operation which comprises introducing steam under pressure to establish within the capillary interstices of the plant material a mixture of air and steam until a pressure of from about five to about fifty pounds per square inch gage pressure is reached, then discontinuin the introduction of steam, and while excluding additional air from said pressure vessel forthwith rapidly withdrawing said mixture of air and steam from said pressure vessel and from the interstice of said plant material until a pressure is reached within the range of from atmospheric pressure to a gage pressure half that which existed when the introduction of steam was discontinued; thereafter immersing said pre-treated plant material in cooking liquor while continuing to exclude air from said plant material, the quantity of cooking liquor being sufiicient to completely submerge said pre-treated plant material; and then cooking said pretreated plant material while completely submerged in cooking liquor.
8. The process of claim 2 in which the pretreating operation is carried out a plurality of times before the plant material is immersed in cooking liquor.
JAMES HAMILTON ROSS. JOHN SEMPLE HART. RICHARD KEVIN STRAPP,
OTHER REFERENCES Chemistry of Pulp and Paper Making, by Sutermeister, 3d Ed, published by John Wiley & Sons, New York (1941) pp. 101 and 187.
Manufacture of Pulp and Paper, 3rd Ed., vol. III, section 5, page 34 (1937), published by Me- Graw-Hill, New York.

Claims (1)

1. IN THE PRODUCTION OF CELLULOSE PULP FROM FIBROUS PLANT MATERIAL, THE PROCESS WHICH CONSISTS OF THE STEPS OF INTRODUCING PLANT MATERIAL IN SUBDIVIDED CONDITION INTO A PRESSURE VESSEL; DISPLACING AIR IN SAID PRESSURE VESSEL WITH STEAM; SUBJECTING SAID PLANT MATERIAL WITHIN SAID PRESSURE VESSEL TO A PRE-TREATING OPERATION WHICH COMPRISES INTRODUCING STEAM UNDER PRESSURE TO ESTABLISH WITHIN THE CAPILLARY INTERSTICES OF THE PLANT MATERIAL A MIXTURE OF AIR AND STEAM UNTIL A PRESSURE OF FROM ABOUT FIVE TO FIFTY POUNDS PER SQUARE INCH GAGE PRESSURE IS REACHED, THEN DISCONTINUING THE INTRODUCTION OF STEAM, AND WHILE EXCLUDING ADDITIONAL AIR FROM SAID PRESSURE VESSEL FORTHWITH RAPIDLY WITHDRAWING SAID MIXTURE OF AIR AND STEAM FROM SAID PRESSURE VESSEL AND FROM THE INSTERSTICES OF SAID PLANT MATERIAL UNTIL A PRESSURE IS REACHED WITHIN THE RANGE OF FROM ATMOSPHERIC PRESSURE TO A GAGE PRESSURE HALF THAT WHICH EXISTED WHEN THE INTRODUCTION OF STEAM WAS DISCONTINUED; THEREAFTER IMMERSING SAID PRE-TREATED PLANT MATERIAL IN COOKING LIQUOR WHILE CONTINUING TO EXCLUDE AIR FROM SAID PLANT MATERIAL; AND THEN COOKING SAID PRE-TREATED PLANT MATERIAL.
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US2749240A (en) * 1953-01-17 1956-06-05 Pulp Paper Res Inst Production of cellulose pulp
US2799579A (en) * 1953-06-22 1957-07-16 Hjalmar S Messing Apparatus for presoaking lignocellulose material
DE1052796B (en) * 1956-01-18 1959-03-12 Pulp Paper Res Inst Process for the continuous or discontinuous production of pulp from wood
DE1063450B (en) * 1956-05-11 1959-08-13 Bauer Bros Company Method and device for the preparation of wood chips or similar cellulose-containing raw materials for the purpose of obtaining semi-cellulose or cellulose
US2932600A (en) * 1953-02-25 1960-04-12 Brown And Root Inc Process for the production of pulp from bagasse
US2985236A (en) * 1957-03-27 1961-05-23 Celleco Ab Impregnation of wood chips
US3013933A (en) * 1953-01-28 1961-12-19 Rayonier Inc Method for preparation of wood cellulose
US3016088A (en) * 1954-09-07 1962-01-09 Bauer Bros Co Rapid cycle digester
US3067086A (en) * 1959-09-15 1962-12-04 Columbia Cellulose Company Ltd Pulping process
US3078208A (en) * 1958-09-11 1963-02-19 Stora Kopparbergs Bergslags Ab Method for the production of neutral sulfite pulp
US3215587A (en) * 1963-01-21 1965-11-02 Lummus Co Continuous process and apparatus for delignification of cellulosic material
US3294625A (en) * 1963-03-28 1966-12-27 Lummus Co Method for impregnating cellulosic material
US4634499A (en) * 1983-05-02 1987-01-06 The Procter & Gamble Company Sulfite process for making pulp having a tactile softness from hardwood chips
US4734162A (en) * 1985-08-14 1988-03-29 The Procter & Gamble Company Hardwood pulp having a tactile sense of softness, and tissue paper webs thereof
US6129816A (en) * 1997-10-24 2000-10-10 Andritz-Ahlstrom Inc. Tapered screen assembly for a cellulose pulp digester
CN113355935A (en) * 2021-06-22 2021-09-07 中国联合装备集团安阳机械有限公司 External pot loading device and cooking pot for papermaking industry and using method thereof
CN115053033A (en) * 2020-02-03 2022-09-13 瑞典乙醇化工技术有限公司 Apparatus and method for pretreatment of biomass

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US2749240A (en) * 1953-01-17 1956-06-05 Pulp Paper Res Inst Production of cellulose pulp
US3013933A (en) * 1953-01-28 1961-12-19 Rayonier Inc Method for preparation of wood cellulose
US2932600A (en) * 1953-02-25 1960-04-12 Brown And Root Inc Process for the production of pulp from bagasse
US2799579A (en) * 1953-06-22 1957-07-16 Hjalmar S Messing Apparatus for presoaking lignocellulose material
US3016088A (en) * 1954-09-07 1962-01-09 Bauer Bros Co Rapid cycle digester
DE1052796B (en) * 1956-01-18 1959-03-12 Pulp Paper Res Inst Process for the continuous or discontinuous production of pulp from wood
DE1063450B (en) * 1956-05-11 1959-08-13 Bauer Bros Company Method and device for the preparation of wood chips or similar cellulose-containing raw materials for the purpose of obtaining semi-cellulose or cellulose
US2985236A (en) * 1957-03-27 1961-05-23 Celleco Ab Impregnation of wood chips
US3078208A (en) * 1958-09-11 1963-02-19 Stora Kopparbergs Bergslags Ab Method for the production of neutral sulfite pulp
US3067086A (en) * 1959-09-15 1962-12-04 Columbia Cellulose Company Ltd Pulping process
US3215587A (en) * 1963-01-21 1965-11-02 Lummus Co Continuous process and apparatus for delignification of cellulosic material
US3294625A (en) * 1963-03-28 1966-12-27 Lummus Co Method for impregnating cellulosic material
US4634499A (en) * 1983-05-02 1987-01-06 The Procter & Gamble Company Sulfite process for making pulp having a tactile softness from hardwood chips
US4734162A (en) * 1985-08-14 1988-03-29 The Procter & Gamble Company Hardwood pulp having a tactile sense of softness, and tissue paper webs thereof
US6129816A (en) * 1997-10-24 2000-10-10 Andritz-Ahlstrom Inc. Tapered screen assembly for a cellulose pulp digester
US6375796B1 (en) 1997-10-24 2002-04-23 Andritz Inc. Method of treating material in a continuous digester
USRE39208E1 (en) * 1997-10-24 2006-08-01 Andritz, Inc. Method of treating material in a continuous digester
CN115053033A (en) * 2020-02-03 2022-09-13 瑞典乙醇化工技术有限公司 Apparatus and method for pretreatment of biomass
CN113355935A (en) * 2021-06-22 2021-09-07 中国联合装备集团安阳机械有限公司 External pot loading device and cooking pot for papermaking industry and using method thereof

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