US20060175029A1 - Batch process for preparing pulp - Google Patents

Batch process for preparing pulp Download PDF

Info

Publication number
US20060175029A1
US20060175029A1 US10/564,373 US56437304A US2006175029A1 US 20060175029 A1 US20060175029 A1 US 20060175029A1 US 56437304 A US56437304 A US 56437304A US 2006175029 A1 US2006175029 A1 US 2006175029A1
Authority
US
United States
Prior art keywords
liquor
cooking
polysulfide
impregnation
digester
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US10/564,373
Other languages
English (en)
Inventor
Seppo Martikainen
Panu Tikka
Olli Timonen
Mikael Svedman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Valmet Technologies Oy
Flsmidth Dorr Oliver Eimco Management Hungary Kft Luxembourg Branch
Original Assignee
Metso Paper Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Metso Paper Oy filed Critical Metso Paper Oy
Assigned to METSO PAPER, INC. reassignment METSO PAPER, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: TIMONEN, OLLI, MARTIKAINEN, SEPPO, TIKKA, PANU, SVEDMAN, MIKAEL
Publication of US20060175029A1 publication Critical patent/US20060175029A1/en
Assigned to GL&V MANAGEMENT HUNGARY KFT, LUXEMBOURG BRANCH reassignment GL&V MANAGEMENT HUNGARY KFT, LUXEMBOURG BRANCH ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: METSO PAPER INC.
Assigned to VALMET TECHNOLOGIES, INC. reassignment VALMET TECHNOLOGIES, INC. CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: METSO PAPER, INC.
Abandoned legal-status Critical Current

Links

Images

Classifications

    • 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
    • D21C1/06—Pretreatment of the finely-divided materials before digesting with alkaline reacting compounds
    • 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
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/0021—Introduction of various effluents, e.g. waste waters, into the pulping, recovery and regeneration cycle (closed-cycle)
    • 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
    • D21C3/222—Use of compounds accelerating the 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
    • D21C3/22—Other features of pulping processes
    • D21C3/26—Multistage processes

Definitions

  • the present invention relates to a process fir preparing kraft pulp in which lignocellulosic material is treated with recycled process liquors, polysulfide and fresh re-causticized white liquor for removing lignin therefrom. More particularly, the present invention relates to the use of polysulfide white liquor (or another polysulfide source) in the early stages of modern displacement kraft batch cooking, and the advantage thereof in terms of improved pulp yield.
  • lignocellulosic material In the various kraft pulping processes, lignocellulosic material, most commonly wood chips, is generally treated at elevated temperatures with alkaline cooking liquor containing sodium hydroxide and sodium hydrogen sulfide, called white liquor. In these processes a significant part of the cellulosic material, especially hemicelluloses, are partly lost due to reactions with the white liquor. In kraft pulping conditions hemicelluloses undergo alkaline peeling reactions, de-polymerization, in which the hemicelluloses are dissolved as organic acids into the cooking liquor. A known fact is that by a polysulfide treatment, hemicelluloses are stabilized and are thereafter more resistant to cooking liquor in kraft cooking conditions, which leads to higher yield from the processes lignocellulosic substance input.
  • kraft pulping processes fresh cooking liquor is obtained from the recovery furnace's inorganic smelt, which is dissolved in water and causticized to produce white liquor.
  • Polysulfide-containing white liquor is obtained from causticized white liquor by various processes, which partially oxidize the liquor's sodium sulfide into polysulfide. These processes typically use oxidation catalysts to polymerize the white liquor's hydrogen sulfide. Also, polysulfide can be produced directly by elemental sulfur addition into white liquor. Polysulfide-containing white liquor is called polysulfide white liquor or orange liquor.
  • polysulfide white liquor has been quite straightforward in conventional kraft cooking operations.
  • the normal white liquor has been converted to polysulfide white liquor, and that liquor has been used in the same manner as normal white liquor.
  • the polysulfide After the impregnation into the wood chips in the digester and during the temperature rise to above 100° C., the polysulfide has reacted with the carbohydrates making them less vulnerable to alkaline degradation. Later during the cook, when temperature has risen over 140° C., the rest of the polysulfide has rapidly broken down through thermal decomposition.
  • all the conventional cooking systems have used cooking liquors having initial temperatures well below 100° C. and the temperature in the digester has been elevated slowly or in steps, the polysulfide has had the possibility to react and facilitate higher pulp yield.
  • White liquor is introduced into the digester as “hot white liquor”, which has been heated up using the heat of the previously generated spent liquor, and steam.
  • hot is meant to designate a liquor having a temperature above its boiling point at ambient pressure, i.e. a liquor that must be stored in a pressurized vessel.
  • the hot white liquor temperature in typical displacement batch cooking is 140-180° C.
  • polysulfide has been an impossible chemical. Polysulfide is unstable at higher temperatures, for instance at those used in kraft cooling; the chemical begins to break down at temperatures above 100° C., and it degrades completely in a few minutes at 150° C. Thus at the typical process temperature of the hot white liquor, polysulfide white liquor is not stable at all. This fact has disabled the use of polysulfide in the modern displacement kraft pulping processes developed for higher energy and chemical economy and improved pulp quality.
  • Characteristic for the displacement kraft batch process is to recover hot black liquor from the end of the cooking by displacement and then re-use the energy in the subsequent batches. Partly this is done by using the hot spent cooking liquor as such, and partly by heating the white liquor with the heat of the hot spent liquor leaving the digester system or collected for re-use at low temperature.
  • This process arrangement leads to high temperatures m the input liquor accumulators.
  • a low temperature white liquor typically at 80° C. in the storage tank after re-causticization, cannot be used anymore, and the environment for stable polysulfide in the white liquor does not exist anymore.
  • a further characteristic feature of a modern displacement batch process is to combine energy efficiency and efficient use of residual and fresh cooking chemicals to achieve, in addition to energy efficiency, high pulp strength and good delignification through hydroxyl and hydrosulfide concentration and temperature profiling at different stages of the cooking cycle (Hiljanen, Tikka, EP-B 520 452, Tikka, U.S. Pat. No. 5,183,535).
  • anthraquinone acts by reducing carbohydrate end groups, stabilising them against alkaline peeling and producing anthrahydroquinone, which is alkali soluble.
  • Anthrahydroquinone reduces lignin, making it more reactive. In this process, anthraquinone is formed again and may react with carbohydrates.
  • the dissolved calcium-containing material has not boon degraded, and the amount of calcium bound to the dissolved material in the black liquor is high As disclosed in publication EP 1 242 674, this problem may be solved by re-introducing liquor having a high calcium precipitating potential into the digester as a displacement liquor at the end of a cook. At this point, the digester temperature is sufficiently high to cause calcium liberation. The calcium is then removed together with the pulp, and does not enter the evaporation and regeneration cycle.
  • a method for producing pulp using polysulfide white liquor involves a kraft batch process which comprises the addition of polysulfide white liquor in the impregnation and pretreatment in the very ‘front-end’ of the cooking process, and a finalizing delignification stage with white liquor and optional cooking catalyst addition, which is facilitated by the modified ‘front-end’ process chemistry resulting in improved pulp yield.
  • a volume of polysulfide white liquor is added as the first portion of liquor to enter the digester, or admixed with the impregnation liquor prior to this being pumped into the digester.
  • impregnation liquor means a liquor stored at a temperature below its atmospheric boiling point, used for a first immersion of the lignocellulosic raw material in a batch pulping process.
  • lignocellulosic material entering a displacement batch process is thus pretreated with polysulfide-containing process liquors in conditions favourable for pre-treatment and polysulfide stability.
  • a set of displacement batch process arrangements capable of taking advantage of the polysulfide white liquor, are presented.
  • the required dose of fresh polysulfide white liquor is introduced in the initial stage of the process.
  • the impregnation stage provides for both impregnation and polysulfide pretreatment reactions.
  • An impregnation liquor circulation collects the displaced impregnation liquor which is re-used to fill and pressurize the digester after the first fresh liquor fill.
  • An optional feature in the present invention is a new way to use a cooking catalyst, such as anthraquinone (AQ).
  • AQ anthraquinone
  • the cooking catalyst can be used to maintain a normal kraft cooking rate and production level.
  • the catalyst may be introduced into the digester together with the hot white liquor. By this means it will not escape due to displacements, and on the other hand, it arrives in the hot cooking stage where it is most needed. As a result, the technical and economical benefits of the displacement batch cooking are retained, while the advantages of polysulfide and cooking catalyst can be fully exploited.
  • FIG. 1 shows a block diagram of a kraft displacement batch cooling system according to the invention.
  • the top of the figure defines the required tanks, leaving or entering streams denoted by letters.
  • the cooking stage sequence is displayed therebelow, chronologically starting from the top and the vertically indicated streams representing the liquors passing through the digester during the various stages.
  • the letters denoting the various entering and leaving streams correspond to the source or destination in the tank scheme.
  • FIG. 2 shows a further embodiment of a kraft displacement batch cooking system according to the invention.
  • the kraft batch cook is started by charging the digester with wood chips, or with another lignocellulosic material. After the lignocellulosic material charge, the digester is filled in a stepwise sequence using a volume of fresh polysulfide white liquor X 1 from polysulfide white liquor tank 6 , and impregnation liquor Al from tank 4 , topping the digester full of liquor.
  • the volume of polysulfide white liquor may be added as a separate first portion, forming a raising pad of liquor as further liquor is pumped in from below. Alternatively, the polysulfide white liquor is mixed into the impregnation liquor.
  • An overflow, A 2 conducted to the impregnation liquor tank 4 , is preferred in order to remove air and the diluted first front of liquor.
  • the digester is pressurized and impregnation is completed during an appropriate period of time.
  • the cooking process is then continued by pumping in a volume of hot black liquor B 1 from hot black liquor accumulator 1 .
  • the cooler impregnation liquor A 3 displaced by hot black liquor, is conducted to impregnation liquor tank 4 to be re-used in subsequent batches.
  • Pumping a volume C of hot white liquor from tank 3 into the digester then continues the cooking sequence. Together with white liquor C, an amount of cooking catalyst may be dosed into the digester.
  • the liquor D 1 displaced by hot liquor above about the atmospheric boiling point, in conducted to hot black liquor accumulator 2 .
  • the digester is close to the final cooking temperature.
  • the final heating-up is carried out using direct or indirect steam heating and digester re-circulation.
  • the spent liquor is ready to be displaced with wash filtrate E 1 from tank 5 .
  • a volume A 4 from impregnation liquor tank 4 may be used as a first portion of displacement liquor in order to deactivate the potential scale-forming calcium therein, as disclosed in EP 1 242 674.
  • the first displaced volume B 2 displaced by wash filtrate is conducted to black liquor accumulator 1 .
  • the second portion D 2 of displaced black liquor which is diluted by the wash filtrate but is still above atmospheric boiling point, is conducted to the hot black liquor accumulator 2 .
  • the digester contents are discharged for further processing of the pulp. The above cooking sequence may then be repeated.
  • the hot black liquor from accumulator 2 is conducted to the evaporation plant, first being used to heat white liquor due for tank 3 , and/or water, by means of heat exchange.
  • Tank 6 is provided for storage of polysulfide white liquor, supplied from a plant for polysulfide generation.
  • a volume of polysulfide white liquor corresponding to 25-90% of the total active alkali dosage and resulting in 0.5% to 5% polysulfide dosage on abs. dry wood is added into the digester before the impregnation fill is completed Impregnation is carried out using temperature ofbetween 70° C. and 120° C., preferably between 85-95° C., and a time of between about 20 to about 120 minutes, preferably between about 30 to about 60 minutes, more preferably between about 25 to about 40 minutes.
  • the polysulfide white liquor is added as a separate portion before the introduction of further liquor.
  • the volume of polysulfide white liquor corresponds to 50-75% of the total active alkali dosage for the relevant batch.
  • a cooking catalyst is used.
  • Preferable catalysts are anthraquinone, anthraquinone sulfonate, and hydroanthraquinone. Any other appropriate redox-catalyst as anticipated by those skilled in the art may be used.
  • hot black liquor accumulators 1 and 2 of FIG. 1 are combined.
  • the black liquor flow to the evaporation plant is drawn from the single hot black liquor accumulator, the stream being used to heat, by means of heat exchange, white liquor heading for white liquor accumulator 3 , and/or water, as shown for tank 2 in FIG. 1 .
  • the stream from impregnation liquor tank 4 to hot black liquor tank 1 may be heated by means of heat exchange with the stream from hot black liquor accumulator 2 to the evaporation plant
  • one or more additional white liquor charges may be carried out during the cook.
  • the principal advantage of the process of the present invention is that the ‘front-end’ of the kraft displacement batch cooking system is rendered more effective from a chemical point of view, and in regard to process arrangements.
  • the polysulfide charge used reflects the improvement in pulp yield from the digested lignocellulosic material.
  • Impregnation black liquor consisting of wash filtrate and white liquor (WBL, 80-90° C., 25 gEA/l) was pumped in during app. 10 minutes followed by impregnation at 90° C. under 2.5 bar overpressure. The duration of the impregnation stage was 40 minutes (WBL-fill and impregnation in total).
  • a hot black liquor pre-treatment stage was commenced by introducing hot black liquor (HBL 1 , 150° C., app.
  • terminal displacement was started by introducing cool DWBL and wash filtrate (WF) in a sequence into the digester bottom displacing the hot spent black liquor out of the digester top (DCBL 2 ).
  • WF wash filtrate
  • the fist displaced portion the hot black liquor with the hot black liquor displaced earlier during the cooking sequence (DCBL 2 +DCBL 1 ) covered the volume needed for the next cook's hot black liquor (HBL 1 ).
  • the terminal displacement stage duration was approximately 40 minutes.
  • the pulp was disintegrated, washed with deionised water, screened and analysed. The cooking procedure was repeated and thus equilibrium in the cooking process was obtained and the cooks started to repeat themselves corresponding to the industrial batch cooking system.
  • Impregnation liquors were introduced as sequence as follows: initially polysulfide white liquor black liquor (PSWL, volume according to the charge, app. 4.5-5 l); subsequently re-circulated spent impregnation liquor (DWBL) to hydraulically fill the digester.
  • PSWL polysulfide white liquor black liquor
  • DWBL spent impregnation liquor
  • the duration of the impregnation stage was 40 minutes (fill sequence and impregnation in total).
  • a hot black liquor pre-treatment stage was carried out by introducing hot black liquor (HBL 1 , 150° C., app. 20 gFA/l) to the bottom of the digester of the digester, displacing the spent impregnation liquor from the top of the digester (DWBL).
  • the hot black liquor pre-treatment stage duration was 30 minutes.
  • hot white liquor 121 gFA (NaOH)/l, sulfidity 37%) charge was introduced, displacing the corresponding volume of spent hot black liquor from the digester (RHBL).
  • a cooking catalyst was charged mixed with a small volume of hot black liquor.
  • a 45 minute heat-u sequence with cooking liquor circulation raised the temperature from 150° C. to the cooling temperature of 167° C.
  • a further white liquor charge was introduced into the digester bottom displacing the corresponding volume of spent hot black liquor from the digester (DCBL 1 ).
  • terminal displacement was started by introducing a volume of cool DWBL and wash filtrate (WF) in a sequence into the digester bottom displacing the hot spent black liquor out of the digester top (DCBL 2 ).
  • the reference cook follows the same addition and temperature sequences as the cooks according to the invention. All cooks were digested to the same target kappa number. A clear yield improvement correlating with polysulfide addition can be observed Cooking PS-charge, % Kappa Total yield, % Rejects, % on model on wood number on wood wood Reference Nil 25.9 44.0 0.26 SB-PSAQ 1.21 25.9 45.8 0.36 SB-PSAQ 1.58 25.8 46.8 0.24

Landscapes

  • Paper (AREA)
  • Polysaccharides And Polysaccharide Derivatives (AREA)
US10/564,373 2003-12-31 2004-12-22 Batch process for preparing pulp Abandoned US20060175029A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FI20031929A FI120361B (fi) 2003-12-31 2003-12-31 Eräkeittomenetelmä kraftmassan valmistamiseksi
FI20031929 2003-12-31
PCT/FI2004/050196 WO2005064075A1 (en) 2003-12-31 2004-12-22 Batch process for preparing pulp

Publications (1)

Publication Number Publication Date
US20060175029A1 true US20060175029A1 (en) 2006-08-10

Family

ID=29763617

Family Applications (1)

Application Number Title Priority Date Filing Date
US10/564,373 Abandoned US20060175029A1 (en) 2003-12-31 2004-12-22 Batch process for preparing pulp

Country Status (7)

Country Link
US (1) US20060175029A1 (fi)
EP (1) EP1702101B1 (fi)
AT (1) ATE423866T1 (fi)
CA (1) CA2530704A1 (fi)
DE (1) DE602004019689D1 (fi)
FI (1) FI120361B (fi)
WO (1) WO2005064075A1 (fi)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090126883A1 (en) * 2007-11-20 2009-05-21 Jianer Jiang Use of polysulfide in modified cooking

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2010202496B2 (en) * 2010-05-04 2015-04-16 Bahia Specialty Cellulose Sa Method and system for high alpha dissolving pulp production
KR20110123184A (ko) 2010-05-06 2011-11-14 바히아 스페셜티 셀룰로스 에스에이 높은 알파 용해 펄프 제조를 위한 방법 및 시스템
PT2567022E (pt) * 2010-05-04 2014-12-23 Bahia Specialty Cellulose Sa Método e sistema para processamento de pasta utilizando extracção cáustica a frio com reutilização de filtrado alcalino
FI127420B (fi) 2011-06-23 2018-05-31 Andritz Oy Menetelmä selluloosamassan valmistamiseksi
FI129362B (fi) 2017-05-16 2021-12-31 Andritz Oy Menetelmä kemiallisen massan tuottamiseksi

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4578149A (en) * 1981-03-05 1986-03-25 Fagerlund Bertil K E Process for digesting cellulosic material with heat recovery
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
US5183535A (en) * 1990-02-09 1993-02-02 Sunds Defibrator Rauma Oy Process for preparing kraft pulp using black liquor pretreatment reaction
US6143130A (en) * 1997-09-09 2000-11-07 Kvaerner Pulping Ab Polysulfide pulping process
US6350348B1 (en) * 1997-01-22 2002-02-26 Andritz-Ahlstrom Oy Batch cooking with black liquor pretreatment

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FI92224C (fi) * 1991-06-28 1994-10-10 Sunds Defibrator Rauma Oy Eräprosessi kraftmassan valmistamiseksi
FI105929B (fi) * 1996-05-30 2000-10-31 Sunds Defibrator Pori Oy Parannettu erämenetelmä sulfaattiselluloosan valmistamiseksi
WO1999014423A1 (en) * 1997-09-18 1999-03-25 Kvaerner Pulping Ab Polysulfide pulping process
FI110327B (fi) * 1999-10-04 2002-12-31 Metso Chemical Pulping Oy Menetelmä sellumassan valmistamiseksi

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4578149A (en) * 1981-03-05 1986-03-25 Fagerlund Bertil K E Process for digesting cellulosic material with heat recovery
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
US5183535A (en) * 1990-02-09 1993-02-02 Sunds Defibrator Rauma Oy Process for preparing kraft pulp using black liquor pretreatment reaction
US5183535B1 (en) * 1990-02-09 1996-02-06 Sunds Defibrator Rauma Oy Process for preparing kraft pulp using black liquor pretreatment reaction
US6350348B1 (en) * 1997-01-22 2002-02-26 Andritz-Ahlstrom Oy Batch cooking with black liquor pretreatment
US6143130A (en) * 1997-09-09 2000-11-07 Kvaerner Pulping Ab Polysulfide pulping process

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090126883A1 (en) * 2007-11-20 2009-05-21 Jianer Jiang Use of polysulfide in modified cooking
US7828930B2 (en) * 2007-11-20 2010-11-09 International Paper Company Use of polysulfide in modified cooking
US20110155335A1 (en) * 2007-11-20 2011-06-30 International Paper Company Use of polysulfide in modified cooking

Also Published As

Publication number Publication date
FI20031929A (fi) 2005-07-01
EP1702101A1 (en) 2006-09-20
EP1702101B1 (en) 2009-02-25
CA2530704A1 (en) 2005-07-14
FI120361B (fi) 2009-09-30
DE602004019689D1 (de) 2009-04-09
WO2005064075A1 (en) 2005-07-14
ATE423866T1 (de) 2009-03-15
FI20031929A0 (fi) 2003-12-31

Similar Documents

Publication Publication Date Title
JP2984798B2 (ja) 前加水分解パルプの製造
US6533896B1 (en) Method for the production of precleaned pulp
EP2430233B1 (en) Method for producing pulp
US20110056637A1 (en) Prehydrolysis sulfate cooking process
EP0810321B1 (en) Batch process for preparing improved kraft pulp
US6413367B1 (en) Treatment of cellulosic material with a chelating agent prior to alkaline delignification
US5183535A (en) Process for preparing kraft pulp using black liquor pretreatment reaction
EP1702101B1 (en) Batch process for preparing pulp
EP0468016B1 (en) Process for preparing kraft pulp
US6939439B1 (en) Batch process for producing chemical pulp by removing and reintroducing calcium-containing spent liquor in the digester
US20040089430A1 (en) Method for alkaline cooking of fiber material
CN116695479A (zh) 硫酸盐竹浆dds蒸煮工艺

Legal Events

Date Code Title Description
AS Assignment

Owner name: METSO PAPER, INC., FINLAND

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MARTIKAINEN, SEPPO;TIKKA, PANU;TIMONEN, OLLI;AND OTHERS;REEL/FRAME:017255/0624;SIGNING DATES FROM 20051014 TO 20051201

AS Assignment

Owner name: GL&V MANAGEMENT HUNGARY KFT, LUXEMBOURG BRANCH, LU

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:METSO PAPER INC.;REEL/FRAME:019925/0103

Effective date: 20061229

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION

AS Assignment

Owner name: VALMET TECHNOLOGIES, INC., FINLAND

Free format text: CHANGE OF NAME;ASSIGNOR:METSO PAPER, INC.;REEL/FRAME:032551/0426

Effective date: 20131212