US3907631A - Method of performing a surge-boil step during the heating period of a lignocellulosic material cooking stage - Google Patents

Method of performing a surge-boil step during the heating period of a lignocellulosic material cooking stage Download PDF

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US3907631A
US3907631A US368032A US36803273A US3907631A US 3907631 A US3907631 A US 3907631A US 368032 A US368032 A US 368032A US 36803273 A US36803273 A US 36803273A US 3907631 A US3907631 A US 3907631A
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digester
surge
steam
boil
cooking
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US368032A
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Sture Olof Erik Backlund
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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
    • 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
    • D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/22—Other features of pulping processes
    • D21C3/26—Multistage processes
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C7/00—Digesters
    • D21C7/10—Heating devices

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  • This invention relates to a'method' of'obtaining homogeneous digestion in the periodic cooking of a lignocellulosic material.
  • surge-boils by supplying direct steam to the digester bottom.
  • the surge-boils are brought about according to the present invention by pressure reduction in the digester and simultaneous direct supply of steam to the digester bottom. Thereby the surgeboils become more efficient, especially during rapid heating processes.
  • the steam supply is to be substantial, i.e., at least 0.1 ton steam/minute, preferably 0.1 0.5 ton steam/minute.
  • the pressure reduction in the digester bringing about a surge-boil is effected either by degassing from the digester top or by supply of cooling liquor, for example cooking liquor or water, to the digester top.
  • At least one of said surge-boil steps is carried out during the heating period of the cooking stage at a point of time when the chlorine number of the pulp is 30-20.
  • the duration of the surge-boil periods may vary, but should be at least 5 seconds.
  • a normal period is seconds minutes, suitably 1 10 minutes and preferably 2 5 minutes.
  • FIG. 1 shows a periodic sulphate digester with a circulation system for indirect heating
  • FIG. 2 shows such a digester with a system for direct heating with steam.
  • the invention is described in the following by way of two examples with reference to the drawings.
  • the examples refer to sulphate cooking, the method achowever, that an important factor in equipped with a circulation system for indirect heating 1 according to'FlG. 1.
  • the digester is charged by means of a liquor packing method with about23 tons of wood chips calculated on the dry basis.
  • 'White liquor and black liquor are charged in an amount such that the alkali charge is 200'kgactive alkali (NaOH) per ton of absolutely 'dry wood, and the'woodfili'quor ratio is 1:35
  • the circulation pump l is started already whilst the chips are being charged, and it sucks liquor from the digester through a strainer unit 2.
  • the cooking liquor is circulated through the heat-exchanger-3 for heating arid is distributed after the heat-exchanger so that 8071 of the volume flow is passed to the top of the digester via a conduit 4 and the remaining 20% is passed to the digester bottom 'via a conduit 5
  • the liquor circulated to the top of the digester is distributed over the chips by means of centrifugal pressure sprays 6.
  • the heating to 170 C is effected within 1 50 minutes by indirect heating with steam in the heat exch anger 3 and during the surge-boils also by direct heating with steam.
  • thc first surge-boil The temperature in the top circulation conduit 4 duringthe heating of the cook having reached 153 C., thc first surge-boil is carried out. This is effected in such a manner that the valve 7 is closed automatically by a time clock which was started at the start of the cooking process.
  • valve 7 Thirty seconds after the closing of valve 7. the dcgassing valve 8 is opened whereby the digester is degassed through the conduit 9, and at the same time the steam valve 10 is opened for supplying direct steam through a conduit 11. After 5 minutes the valves 8 and 10 are closed, and the valve 7 is opened.
  • the heating of the cook can thereafter proceed in a normal way.
  • a surge-boil takes place in the digester, which owing to the steam supply becomes relatively insensitive to over-pressure in the digester.
  • the same surge-boil step is repeated also at C. and at 167 C.
  • the cook is held at the maximum temperature of 170 C. for about 1 hour.
  • the digester is blown. Blowing time 30 minutes.
  • the chlorine number of the pulp was 5.7 and the shive content when screening an average sample from the cook in a Wennberg-strainer having a slit width of 0.20 mm was 1.0%.
  • EXAMPLE 2 The cooking is carried out in a periodic sulphate digester having a volume of 125 m according to FIG. 2.
  • the digester is equipped for direct heating by steam.
  • the digester is charged with wood chips, which are packed by means of a steam packing unit so that the amount of chips in the digester is about 25 tons of chips calculated on the dry basis.
  • White liquor and black li quor are charged in a amount such that the alkali charge is 200 kg of active alkali (NaOH) per ton of absolutely dry wood, and the wood:liquor ratio is 1:30
  • the cook is heated by the supply of direct steam through the conduit 14 to the bottom of the digester.
  • the steam supply iscontrolled by the valve 15 so that the heating to 170C is effected within 30 minutes.
  • de-gassing of air, turpentine, etc.,' takes place all the time in a normal manner through the conduit 16 and with de-gassing control by the valve 17.
  • the first surge-boil is carried out. This is effected by opening the valve 13 for minutes so that a substantial de-gassing takes place through the conduit 12.
  • the surge-boil .de-gassing is to be so substantial that at each surge-boil 0.5 5% of the total liquor amount is removed from the digester.
  • the de-gassed liquor thereby removed comprises about 5 25% steam, the remainder being foam and liquor droplets.
  • the second surge-boil is effected by again opening the valve 13 for 5 minutes and simultaneously also charging steam by opening the valve 15.
  • the steam is to be charged in an amount of the magnitude 0.1 0.5 ton steam/minute.
  • the chlorine number of the pulp was 6.0 and the shive content when straining an average sample from the cook in a Wennberg-strainer with slit width 0.20 mm was 1.5%.
  • the shive content was 7.0% at a chlorine number, of 6.0.
  • a method of improving the homogeneity in periodic cooking of lignocellulosic material in a digester including a heating stage and having a heating system constructed in a manner to permit steam to be supplied directly to the bottom of the digester wherein at least onesurge-boil step having a duration of from 10 min utes to 5 seconds is carried out, during the heating period of the cooking stage at a point of time when the chlorine number of the pulp is 3020, by pressure reduction in the digester, said pressure reduction being obtained by carrying out at least one of the steps of (a) removing gas from'the top of the digester and (b) supplying cooling liquid to the top of the digester, the improvement which consists in enhancing the surge-boil step by simultaneously with the pressure reduction directly supplying steam to the digester bottom in an amount of at least 0.1 ton steam/minute.

Abstract

In the periodic cooking of lignocellulosic material in a digester, the homogeneity of the digester contents can be improved by the interposition of at least one surge-boil during the cooking process which is effected by reducing the pressure in the digester together with the direct introduction of steam into the bottom of the digester, simultaneous with pressure reduction, at a rate of at least 0.1 ton steam/minute.

Description

United States Patent Backlund 1*Sept. 23, 1975 1 METHOD OF PERFORMING A SURGE-BOIL [58] Field of Search 162/42. 6]
STEP DURING THE HEATING PERIOD OF A LIGNOCELLULOSIC MATERIAL Referencfi Cited COOKING STAGE UNITED STATES PATENTS 7 Inventor; Su ()l f i Backlund, 1.831.206 11/1931 Swanson ct al. 162/61 X Sundsvan, Sweden 1905.050 4/1933 Pelot et al v 162/6] 3.298.889 1/1967 Laakso 162/42 x Notice: The portion of the term of this 3 467 573 9/1969 Vogel 162/42 X patent subsequent to Feb. 19, 1991, has been disclaimed. Primary E.\aminerS. Leon Bashore [22] Filed: June 8, 1973 Assistant Examiner-Arthur L. Corbin pp 368,032 57] ABSTRACT R l t d [1,3, A li ti D t In the periodic cooking of lignocellulosic material in a [63] Continumiommpan of No. 209,883 20 digester, the homogeneity of the digester contents can 1971, PM No. 3391137. be improved by the interposition of at least one surgeboil during the cooking process which is effected by 30 Foreign Application p i it Data reducing the pressure in the digester together with the 14 1973 S 7306760 direct introduction of steam into the bottom of the diay v we en v gestcr, slmultaneous w1th pressure reduction, at a rate 52 us. c1 162/42; 162/61 of at east Steam/mum- [5 l] Int. Cl. DZIC 7/12 I Claim, 2 Drawing Figures US Patent Sept. 23,1975 Sheet 2 0f 2 3,907,631
FIG.2
METHOD OF PERFORMING A SURGE-BOIL STEP DURING THE HEATING PERIOD OF'A LIGNOCELLULOSIC MATERIALCOOKING STAGE 'This application is a eontinuation-in-part' ofmy copending Application Ser. No. 209,883 filed Dec. 20, 1971 now U.S.Pat. No. 3,793,137;
This invention relates to a'method' of'obtaining homogeneous digestion in the periodic cooking of a lignocellulosic material.
In all pulp manufacturingprocesses uniform cooking is of great importance, with respect both to economy and to the quality of thepulp. Thc' reasons 'for nonuniform cooking vary with the process type. The Swedish Pat. Spec. No. 545,885 enumerates the most important factors affecting the homogeneity at periodic cooking and it describcs'a method which hasas its object to eliminate the most dominating one of these factors, viz, the cooking liquor circulation. I I
Experiences from a mill installation prove that the techniques applied according to the method, i.e., surgeboil, has a very positive effect on the homogeneity of the cooking.
It was found, conjunction with the surge-boil method was the gassing condition of the digesters, i.e.. the overpressure of air and other gases in the digester when the surge-boil commences during the cooking process. An effective degassing of the digesters prior to the surge-boils is one condition for obtaining a full surge-boil effect, i.e., a fully satisfactory digestion uniformity in the digester.
1t has proved difficult, however, to carry out a complete degassing of the digesters in time before the surge-boil stage, particularly in the case of rapid heating processes.
When experiments were made for overcoming these difficulties, it was found by surprise that the system could be rendered less sensitive to overpressure at the.
surge-boils by supplying direct steam to the digester bottom.
The surge-boils, thus, are brought about according to the present invention by pressure reduction in the digester and simultaneous direct supply of steam to the digester bottom. Thereby the surgeboils become more efficient, especially during rapid heating processes. The steam supply is to be substantial, i.e., at least 0.1 ton steam/minute, preferably 0.1 0.5 ton steam/minute.
The pressure reduction in the digester bringing about a surge-boil is effected either by degassing from the digester top or by supply of cooling liquor, for example cooking liquor or water, to the digester top.
At least one of said surge-boil steps is carried out during the heating period of the cooking stage at a point of time when the chlorine number of the pulp is 30-20.
The duration of the surge-boil periods may vary, but should be at least 5 seconds. A normal period is seconds minutes, suitably 1 10 minutes and preferably 2 5 minutes.
FIG. 1 shows a periodic sulphate digester with a circulation system for indirect heating, and
FIG. 2 shows such a digester with a system for direct heating with steam.
The invention is described in the following by way of two examples with reference to the drawings. Although the examples refer to sulphate cooking, the method achowever, that an important factor in equipped with a circulation system for indirect heating 1 according to'FlG. 1. The digester is charged by means of a liquor packing method with about23 tons of wood chips calculated on the dry basis. 'White liquor and black liquor are charged in an amount such that the alkali charge is 200'kgactive alkali (NaOH) per ton of absolutely 'dry wood, and the'woodfili'quor ratio is 1:35
The circulation pump lis started already whilst the chips are being charged, and it sucks liquor from the digester through a strainer unit 2. The cooking liquor is circulated through the heat-exchanger-3 for heating arid is distributed after the heat-exchanger so that 8071 of the volume flow is passed to the top of the digester via a conduit 4 and the remaining 20% is passed to the digester bottom 'via a conduit 5 The liquor circulated to the top of the digester is distributed over the chips by means of centrifugal pressure sprays 6. The heating to 170 C is effected within 1 50 minutes by indirect heating with steam in the heat exch anger 3 and during the surge-boils also by direct heating with steam. The temperature in the top circulation conduit 4 duringthe heating of the cook having reached 153 C., thc first surge-boil is carried out. This is effected in such a manner that the valve 7 is closed automatically by a time clock which was started at the start of the cooking process.
Thirty seconds after the closing of valve 7. the dcgassing valve 8 is opened whereby the digester is degassed through the conduit 9, and at the same time the steam valve 10 is opened for supplying direct steam through a conduit 11. After 5 minutes the valves 8 and 10 are closed, and the valve 7 is opened.
The heating of the cook can thereafter proceed in a normal way. During said degassing and simultaneous steam supply to the digester bottom. a surge-boil takes place in the digester, which owing to the steam supply becomes relatively insensitive to over-pressure in the digester. The same surge-boil step is repeated also at C. and at 167 C. The cook is held at the maximum temperature of 170 C. for about 1 hour. Subsequent to the in-takc of about 10 m cooling liquor. the digester is blown. Blowing time 30 minutes.
The chlorine number of the pulp was 5.7 and the shive content when screening an average sample from the cook in a Wennberg-strainer having a slit width of 0.20 mm was 1.0%. The shive content of a cook, at which the surge-boil technique was not utilized, was 5.2% at a chlorine number of 5.7.
EXAMPLE 2 The cooking is carried out in a periodic sulphate digester having a volume of 125 m according to FIG. 2. The digester is equipped for direct heating by steam. The digester is charged with wood chips, which are packed by means of a steam packing unit so that the amount of chips in the digester is about 25 tons of chips calculated on the dry basis. White liquor and black li quor are charged in a amount such that the alkali charge is 200 kg of active alkali (NaOH) per ton of absolutely dry wood, and the wood:liquor ratio is 1:30
The cook is heated by the supply of direct steam through the conduit 14 to the bottom of the digester. The steam supply iscontrolled by the valve 15 so that the heating to 170C is effected within 30 minutes. During the cooking step de-gassing of air, turpentine, etc.,' takes place all the time in a normal manner through the conduit 16 and with de-gassing control by the valve 17.
The temperature in the top of the digester having reached 155C, the first surge-boil is carried out. This is effected by opening the valve 13 for minutes so that a substantial de-gassing takes place through the conduit 12. The surge-boil .de-gassing is to be so substantial that at each surge-boil 0.5 5% of the total liquor amount is removed from the digester. The de-gassed liquor thereby removed comprises about 5 25% steam, the remainder being foam and liquor droplets.
The heating of the cook by direct steam continues during the surge-boil'pcriod in a normal manner.
Thev temperature in the digester having reached 170C, the steam supply is interrupted by closing the valve 15.
After 5 minutes at 170C the second surge-boil is effected by again opening the valve 13 for 5 minutes and simultaneously also charging steam by opening the valve 15. The steam is to be charged in an amount of the magnitude 0.1 0.5 ton steam/minute.
After completing the second surge-boil the valves (13) and are again closed.
The chlorine number of the pulp was 6.0 and the shive content when straining an average sample from the cook in a Wennberg-strainer with slit width 0.20 mm was 1.5%. For a cook in which the surge-boiltechnique was not utilized, the shive content was 7.0% at a chlorine number, of 6.0.
'1 claim:
1. ln a method of improving the homogeneity in periodic cooking of lignocellulosic material in a digester including a heating stage and having a heating system constructed in a manner to permit steam to be supplied directly to the bottom of the digester wherein at least onesurge-boil step having a duration of from 10 min utes to 5 seconds is carried out, during the heating period of the cooking stage at a point of time when the chlorine number of the pulp is 3020, by pressure reduction in the digester, said pressure reduction being obtained by carrying out at least one of the steps of (a) removing gas from'the top of the digester and (b) supplying cooling liquid to the top of the digester, the improvement which consists in enhancing the surge-boil step by simultaneously with the pressure reduction directly supplying steam to the digester bottom in an amount of at least 0.1 ton steam/minute.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,907,631
DATED 3 September 23,1975 |NVENTOR(5) 1 Sture Olof Erik Backlund It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
[73] Assignee: SCA Projekt Aktiebolag Signed and Scaled this ninth a O D y f December 1975 Attest:
RUTH- C. MApSON C. MARSHALL DANN Aniflmg ff Commissioner oflarents and Trademarks

Claims (1)

1. IN A METHOD OF IMPROVING THE HOMOGENEITY IN PERIODIC COOKING OF LIGNOCELLULOSIC MATERIAL IN A DIGESTER INCLUDING A HEATING STAGE AND HAVING A HEATING SYSTEM CONSTRUCRED IN A MANNER TO PERMIT STEAM TO BE SUPPLIED DIRECTLY TO THE BOTTOM OF THE DIGESTER WHEREIN AT LEAST ONE SURGE-BOI STEP HAVING A DURATION OF FROM 10 MINUTES TO 5 SECONDS IS CARRIED OUT, DURING THE HEATING PERIOD OF THE COOKING STAGE AT POINT OF TIME WHEN THE CHLORINE NUMBER OF THE PULP IS 30-20, BY PRESSURE REDUCTION IN THE DIGESTER, SAID PRESSURE REDUCTION BEING OBTAINED BY CARRYING OUT AT LEAST ONE OF THE STEPS OF (A) REMOVING GAS FROM THE TOP OF THE DIGESTER AND (B) SUPPLYING COOLING LIQUID TO THE TOP OF THE DIGESTER, THE IMPROVEMENT WHICH CONSISTS IN ENHANCING THE SURGE-BOIL STEP BY SIMULTANEOUSLY WITH THE PRESSURE REDUCTION DIRECTLY SUPPLYING STEAM TO THE DIGESTER BOTTOM IN AN AMOUNT OF AT LEAST 0.1 TON STEAM/MINUTE.
US368032A 1971-12-20 1973-06-08 Method of performing a surge-boil step during the heating period of a lignocellulosic material cooking stage Expired - Lifetime US3907631A (en)

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US20988371A 1971-12-20 1971-12-20
SE7306760A SE434411B (en) 1973-05-14 1973-05-14 WAY TO IMPROVE HOMOGENITY BY PERIODIC COOKING OF LIGNOCELLULOS MATERIAL
US368032A US3907631A (en) 1971-12-20 1973-06-08 Method of performing a surge-boil step during the heating period of a lignocellulosic material cooking stage

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4188261A (en) * 1975-04-18 1980-02-12 Sca Development Aktiebolag Method of improving the homogeneity of lignocellulose containing material

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1831206A (en) * 1931-03-06 1931-11-10 Paper Patents Co Digester system
US1905050A (en) * 1932-04-29 1933-04-25 Nekoosa Edwards Paper Co Apparatus for and method of cooking wood pulp
US3298889A (en) * 1963-05-20 1967-01-17 Meyer Geo J Mfg Co Label picker apparatus
US3467573A (en) * 1965-12-13 1969-09-16 Improved Machinery Inc Upflow digester containing means for separate removal of wash liquor and pulping liquor and method of pulping in said digester

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1831206A (en) * 1931-03-06 1931-11-10 Paper Patents Co Digester system
US1905050A (en) * 1932-04-29 1933-04-25 Nekoosa Edwards Paper Co Apparatus for and method of cooking wood pulp
US3298889A (en) * 1963-05-20 1967-01-17 Meyer Geo J Mfg Co Label picker apparatus
US3467573A (en) * 1965-12-13 1969-09-16 Improved Machinery Inc Upflow digester containing means for separate removal of wash liquor and pulping liquor and method of pulping in said digester

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4188261A (en) * 1975-04-18 1980-02-12 Sca Development Aktiebolag Method of improving the homogeneity of lignocellulose containing material

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SE434411B (en) 1984-07-23

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