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EP0748412B1 - Impact of temperature and alkali charge on pulp brightness - Google Patents

Impact of temperature and alkali charge on pulp brightness Download PDF

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Publication number
EP0748412B1
EP0748412B1 EP95912729A EP95912729A EP0748412B1 EP 0748412 B1 EP0748412 B1 EP 0748412B1 EP 95912729 A EP95912729 A EP 95912729A EP 95912729 A EP95912729 A EP 95912729A EP 0748412 B1 EP0748412 B1 EP 0748412B1
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EP
European Patent Office
Prior art keywords
liquor
cooking
black liquor
digester
rdh
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.)
Expired - Lifetime
Application number
EP95912729A
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German (de)
English (en)
French (fr)
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EP0748412A1 (en
Inventor
Nam Hee Shin
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Beloit Technologies Inc
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Beloit Technologies Inc
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Publication of EP0748412B1 publication Critical patent/EP0748412B1/en
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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
    • 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
    • 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
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/22—Other features of pulping processes

Definitions

  • the present invention relates to a process for delignifying and improving the final brightness of pulp. More particularly, the present invention relates to modifications in both the cooking temperature and white liquor charge for a rapid displacement heating cooking system.
  • Rapid Displacement Heating is a low energy batch cooking process for producing kraft pulp. Combining the inherent advantages of batch cooking with the energy efficiencies of a continuous digester, RDH reuses the spent black liquors that are displaced from a cooked digester to pretreat the wood chips in a consequent cook. Thus, both the chemicals and the heat in these spent liquors are recycled to a consequent cook.
  • the pretreatment of fresh wood chips in a consequent cook begins with lower temperature liquors (approximately 80 ⁇ 130°C), and is followed by high temperature liquors (approximately 130° to 165°C) which heat the digester to the highest possible temperature before raising the temperatures to the final cooking temperature ( 3 170°C) with steam.
  • SU-A-1 498 857 and US-A-1 687 076 are representative of the addition of white liquor to black liquor during impregnation of wood chips in a batch type cooking process, but do not relate to a RDH process.
  • US-A-4,578,149 and EP-A-0 135 461 teach the basic principles of typical RDH type cooking systems. Specifically, in US-A-4,578,149 there is disclosed a batch digesting process of the type using rapid displacement heating to produce delignified pulp, wherein spent liquor produced in a digeter as a result of cooking a mass of cellulosic material with cooking liquor is displaced and collected in accumulators as hot black liquor and as warm black liquor so as to conserve and utilize the heat of the spent liquor to preheat another mass of cellulosic material in warm black liquor and hot black liquor displacement type pretreatments with progressivly hotter spent liquors prior to cooking.
  • the cooking temperature of the batch ranges from 165°C to 177°C.
  • RDH and other alkaline cooking processes produce pulp that is relatively dark in color. Greater contrast is usually needed for the many uses of pulp and paper, so pulp is usually bleached to a high brightness in order to make white pulp for writing and printing papers and paperboard. Pulp color arises from changes in the lignin component of the raw material which occur in the pulping process .
  • high cooking temperatures and low black liquor strength in the RDH process low bleachability problems have occurred following the use of conventional, ECF and TCF bleacning processes. High cooking temperatures and low black liquor strength seem to accelerate condensation reactions, resulting in the condensation of lignin with lignin and other wood extractives. As a result, the bleachability of pulp decreased.
  • the object of the present invention is to improve the prior art pulp bleachability in the RDH process.
  • the batch digesting process of the invention comprises the features of claim 1.
  • the present invention provides a process for improving pulp brightness. Based on modifications to a batch cooking process utilizing rapid displacement heating, the method of the present invention combines the steps of adding white liquor solution (% active alkalinity (AA) or effective alkalinity (EA)) or NaOH to both the warm fill and initial hot fill stages and cooking wood chips at lower temperatures than previously used in a batch type operation to produce pulp that has improved bleachability.
  • white liquor solution % active alkalinity (AA) or effective alkalinity (EA)
  • NaOH sodium nitrate
  • AA active alkalinity
  • EA effective alkalinity
  • a total white liquor charge ranging from 15% AA ⁇ 35% AA is distributed over the warm, hot and cooking stages in a predetermined amount.
  • cool white liquor is also added to the black liquor that is released from the cool liquor accumulator. Essentially, white liquor is added to every stage of the batch cooking process prior to the actual cook.
  • FIG. 1 illustrates a schematic view of a digester and its associated equipment used in the current RDH cooking system.
  • FIGS. 2A, 2B and 2C each illustrate white liquor profiling or the addition of white liquor at various stages of the RDH cooking process.
  • plot A represents the addition of a small amount of white liquor at the beginning of the warm fill mode.
  • Plot B represents the cooking stage and illustrates the presence of white liquor in the digester during the actual cooking of the chips.
  • FIG. 2B illustrates the continuous addition of white liquor to the black liquor at each stage of the RDH cooking process, beginning with the warm fill and continuing through the end of the hot fill.
  • White liquor as shown, is also present in the digester during the actual cook.
  • FIG. 2C illustrates the continuous addition of white liquor at each RDH stage including the addition of white liquor to the washer filtrate from the displacement tank.
  • FIG. 3 illustrates a Stage 3 RDH system without white liquor addition during the warm and hot fill modes.
  • FIG. 4 illustrates a Stage 3 RDH system with the addition of white liquor during the warm and hot fill modes.
  • FIG. 5 illustrates a plot of D1-brightness versus total (D100 + D1) available chlorine charge for the best case and baseline case RDH pulps.
  • Plot A represents RDH pulp R3 (0.225 Kappa factor).
  • Plot B represents RDH pulp R4 (0.27 Kappa factor).
  • Plot C represents RDH pulp R7 (0.225 Kappa factor).
  • Plot D represents RDH pulp R8 (0.27 Kappa factor).
  • FIG. 5A illustrates a plot of D1-brightness versus D1-chlorine dioxide charge.
  • Plot A represents RDH pulp R3 (0.225 Kappa factor).
  • Plot B represents RDH pulp R4 (0.27 Kappa factor).
  • Plot C represents RDH pulp R7 (0.225 Kappa factor).
  • Plot D represents RDH pulp R8 (0.27 Kappa factor).
  • FIG. 6 illustrates the D1-brightness versus the total available chlorine charge in the D100- and D1-stages for all 0.225 Kappa factor bleaches.
  • Plot A represents RDH pulp R3.
  • Plot B represents RDH pulp R12.
  • Plot C represents RDH pulp R7.
  • FIG. 6A illustrates the D1-brightness versus the D1-stage chlorine dioxide charges.
  • Plot A represents RDH pulp R3 (0.225 Kappa factor).
  • Plot B represents RDH pulp R12 (0.225 Kappa factor).
  • Plot C represents RDH pulp R7 (0.225 Kappa factor).
  • FIG. 7 illustrates the D1-brightness versus the total available chlorine charge in the D100- and D1-stages for all 0.27 Kappa factor bleaches.
  • Plot A represents RDH pulp R4.
  • Plot B represents RDH pulp R12.
  • Plot C represents RDH pulp R8.
  • FIG. 7A illustrates the D1-brightness versus the D1-stage chlorine dioxide charges.
  • Plot A represents RDH pulp R4 (0.27 Kappa factor).
  • Plot B represents RDH pulp R12 (0.27 Kappa factor).
  • Plot C represents RDH pulp R8 (0.27 Kappa factor).
  • the present invention as described in claim 1 provides a process for improving pulp bleachability, which is based on modifications to the existing RDH Cooking System for the digestion of wood chips. More specifically, the process involves the addition of a white liquor charge commencing at the start of the RDH cooking cycle and continuing until the time to temperature stage of the process, at which time the actual cook begins.
  • the process of the present invention is also predicated on the use of somewhat lower cooking temperatures for the actual cook as compared to cooking temperatures commonly used in the RDH pulping process.
  • a total white liquor charge ranging between approximately 15%AA ⁇ 35%AA is distributed over the warm black liquor, initial hot black liquor and cooking stages.
  • the cool pad or cool liquor accumulator also receives a white liquor charge.
  • the present invention utilizes lower cooking temperatures ranging between approximately 150°C ⁇ 167°C. As a result, pulp is produced which, upon bleaching with any combination of bleaching chemicals, is improved in final brightness.
  • FIG. 1 schematically illustrates the type of apparatus for RDH that is used for the digestion of pulp. It should be understood that this figure illustrates very general features of the cooking apparatus, and modifications and variations in this system are indeed made as will be discussed in greater detail below. Many instrumentalities such as gauges, pressure vents, pumps and valves have been eliminated from the figures disclosed herein for reasons of simplicity.
  • FIG. 1 is used to illustrate the existing RDH cooking process and to facilitate an understanding of the improvements to the process in accordance with the principles of the present invention.
  • a digester is illustrated at 10 of the type generally used in the chemical digestion of wood chips.
  • the digester 10 has a truncated bottom 12.
  • An inlet valve 14 controls the entry of various reactive liquors into digester 10.
  • the contents of digester 10 can be heated to a final cooking temperature by pumping cooking liquor through a heat exchanger or steam sparger which is connected to digester 10 by a valve-controlled line.
  • cool black liquor temperature around 70°-95°C
  • cool liquor accumulator (A tank) 16 is pumped by means of pump 18 through line 20 which is controlled by a valve 22 into the bottom of the digester 10 through an inlet valve 14.
  • warm black liquor temperature between approximately 90°-150°C
  • warm liquor accumulator 24 is pumped out by means of a pump 18 through a valve 22 and through valve 14 into the bottom of digester 10.
  • this warm liquor fill some black liquor is displaced from the digester 10 and then returned by a line 26 to the cool liquor accumulator 16.
  • Hot black liquor (temperature between 150°-168°C) is then pumped from the hot liquor accumulator (C tank) 28 by means of a pump 30 which is controlled by a valve 32 into the bottom of the digester 10 utilizing valve 14.
  • black liquor is displaced from the digester 10 and returned to the warm liquor accumulator 24 and hot liquor accumulator 28 through lines 34 and 36, respectively.
  • hot white liquor stored in the hot white liquor accumulator 38 is pumped out by means of a pump 30 where it combines with the hot black liquor leaving the hot liquor accumulator 28, the combined liquors then passing through a valve 32 and into the base of the digester 10.
  • the inlet and outlet valves to the digester 10 are closed as the time to temperature stage commences. Steam is injected into the digester 10 and the temperature is increased to the cooking temperature, which averages approximately 170°C. The temperature of the digester is maintained at about this temperature until the wood chips are digested, depending on white liquor charge and H-factor.
  • washer filtrate (temperature approximately 70 ⁇ 85°C) stored in a displacement tank (D tank) 40 is pumped into the digester 10, utilizing pump 42 and valve 44. The contents are washed and the digester 10 is cooled. As the washer filtrate is added to the digester 10, the spent liquors are displaced and returned to the warm liquor accumulator 24 and the hot liquor accumulator 28 by lines 46 and 48, respectively. The displacement mode is concluded when all washer filtrate is used, which is based on the dilution factor of the washer. After displacement is completed, the digested pulp is then pumped out of the digester 10 to a discharge tank using pump 50.
  • the present invention overcomes these problems and improves pulp bleachability by modifying the cooking process for wood chips.
  • This improved RDH process utilizes a combination of higher alkalinity (or white liquor charge) and lower cooking temperatures. More specifically, white liquor is added during the warm and initial hot fill stages. This is in contrast to the existing RDH cooking process, wherein white liquor is added only during the middle of the hot fill mode. Further, when a cool pad is used in the present invention, white liquor is added to the cool black liquor leaving the cool liquor accumulator (or A tank).
  • white liquor is added during each stage to the black liquor.
  • white liquor profiling is illustrated in greater detail below in FIGS. 2A, 2B and 2C.
  • plot A illustrates the addition of a small amount of white liquor at the beginning of the warm fill mode when warm black liquor leaves the B tank or warm liquor accumulator and flows to the digester.
  • White liquor can also be added to the A tank or cool pad when used.
  • Plot B represents the cooking stage and illustrates the presence of white liquor in the digester during the actual cooking of the chips. Black liquor is also present during the cook.
  • FIG. 2B illustrates the continuous addition of white liquor to black liquor at each stage of the cooking process, beginning with the warm fill through the end of the hot fill mode.
  • FIG. 2C illustrates the continuous addition of white liquor throughout the various stages, including the addition of white liquor to the washer filtrate from the displacement tank.
  • FIG. 3 illustrates a Stage 3 RDH system where no white liquor is added during the warm and hot fill modes. Only warm black liquor is leaving the warm liquor accumulator (B tank) 24 to flow through line 56 during the warm fill mode and into line 20, which then empties into the digester 10.
  • this RDH system contains two hot liquor accumulators 28 (C1 tank) and 58 (C2 tank), respectively, there are RDH pulping processes which utilize only one hot liquor accumulator.
  • the process of white liquor profiling can be applied to systems having any number of black liquor accumulators.
  • hot black liquor leaves the hot liquor accumulators 28 and 58 by lines 60 and 62, respectively, and flows to the digester 10 through lines 64 and 20.
  • hot white liquor from the hot white liquor accumulator 38 mixes with the hot black liquor leaving hot liquor accumulator 58 by line 66. The mixture then flows through lines 64 and 20 and into the digester 10.
  • FIG. 4 illustrates a Stage 3 RDH System with the addition of white liquor during the warm and hot fill modes.
  • white liquor is added to the warm black liquor leaving the warm liquor accumulator 24 by line 70.
  • the warm fill flows through lines 56 and 20 into the digester 10.
  • Either cool or hot white liquor may be used during the warm fill mode.
  • hot white liquor from the hot white liquor accumulator 38 is mixed with black liquor leaving hot liquor accumulator 28 by line 72, and is further mixed with the black liquor exiting 'the second hot liquor accumulator 58 by lines 62 and 66.
  • the mixture of hot white and black liquors flows from the two hot liquor accumulators 28 and 58 through lines 64 and 20 into the digester 10.
  • concentration of dissolved organic compounds at initial hot fill operation can be adjusted by adding white liquor to the hot fill line.
  • concentration of dissolved organic compounds in the C1 black liquor and in the C2 black liquor decreases from 13.1% to 10.1% and 14.9% to 9.8%, respectively.
  • warm black liquor temperatures between approximately 70° and 150°C and its strength between 3 and 20 g/l AA
  • hot black liquor temperatures between approximately 100° and 168°C and its strength between 8 and 30 g/l AA
  • warm and hot black liquor can be modified using white liquor profiling. These liquors can also be modified by sodium hydroxide (NaOH) profiling.
  • NaOH sodium hydroxide
  • the addition of white liquor or NaOH controls the total dissolved solids (TDS) concentration and black liquor strength using any combination of black liquor, white liquor and NaOH.
  • the washer filtrate displacement stage in which the black liquor temperature is held between approximately 50° and 105°C and black liquor strength between 1 and 18 g/l AA, can be reinforced with any combination of white liquor or NaOH solution.
  • Tables 1, 1A, 2, 2A, 3 and 3A provide the pulping results and conditions for a number of cooks used in preparing the RDH pulps for subsequent bleaching studies.
  • a summary of the pulping results is provided in Table 3B.
  • RDH Pulping Conditions and Results "Best Case" Cook Number
  • HOT FILL Hot liquor charge, L 18 18 18 18.7 Charge time, min 13 13 13 13 Temperature , C Top 129 132 132 132 Bottom 145 147 145 Chemical conditions in Accumulator: AA(Na2O), g/L 27.8 25.9 27.3 25.3 27.1 24.6 26.5 23.4 EA (Na2O), g/L 19.9 18.9 19.9 18.3 20.2 18.3 19.5 7 17 Na2S (Na2O), g/L 15.8 13.4 14.9 13.9 13.9 12.6 13.9 12.6 TTA (Na2O), g/L - - - - - - Sulfidity, % on A.A.
  • RDH pulps were bleached using an (O)(D100)(EO)(D) sequence. However, each of the five RDH pulps were first oxygen delignified in stirred reactors using the conditions shown below in Table 4.
  • OXYGEN DELIGNIFICATION CONDITIONS Best Case Baseline Case "Do-able " Best Case Sample identification
  • R3 R4 R7 R8 R12 Species Aspen Aspen Aspen Aspen Aspen Aspen Aspen Cook type
  • FIGS. 7 and 7A show that the best do-able case RDH pulp (R12) gave intermediate brightness between the best case RDH pulp (R4) and the baseline case RDH pulp (R8).

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  • Polysaccharides And Polysaccharide Derivatives (AREA)
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  • Peptides Or Proteins (AREA)
  • Medicines Containing Antibodies Or Antigens For Use As Internal Diagnostic Agents (AREA)
EP95912729A 1994-03-04 1995-03-02 Impact of temperature and alkali charge on pulp brightness Expired - Lifetime EP0748412B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US20649694A 1994-03-04 1994-03-04
US206496 1994-03-04
PCT/US1995/002719 WO1995023891A1 (en) 1994-03-04 1995-03-02 Impact of temperature and alkali charge on pulp brightness

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EP0748412A1 EP0748412A1 (en) 1996-12-18
EP0748412B1 true EP0748412B1 (en) 1998-10-21

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EP (1) EP0748412B1 (sv)
JP (1) JP2876428B2 (sv)
CN (1) CN1143398A (sv)
AT (1) ATE172503T1 (sv)
AU (1) AU684623B2 (sv)
BR (1) BR9506974A (sv)
CA (1) CA2184706C (sv)
DE (1) DE69505503T2 (sv)
ES (1) ES2126263T3 (sv)
FI (1) FI118348B (sv)
MX (1) MX9603876A (sv)
NO (1) NO963520L (sv)
NZ (1) NZ282616A (sv)
PL (1) PL316144A1 (sv)
RO (1) RO117929B1 (sv)
RU (1) RU2127342C1 (sv)
TW (1) TW270159B (sv)
WO (1) WO1995023891A1 (sv)
ZA (1) ZA951777B (sv)

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FI970254A (sv) * 1997-01-22 1998-07-23 Ahlstrom Machinery Oy Förfarande och apparatur för massakokning
US6139689A (en) * 1997-06-11 2000-10-31 Beloit Technologies, Inc. Apparatus for digesting pulp in a displacement batch digester that uses displacement liquor having a sufficient hydrostatic head
FI20001351A0 (sv) * 2000-06-06 2000-06-06 Valmet Chemical Pulping Oy Förfarande för satsvis kokning
SE529475C2 (sv) * 2006-11-22 2007-08-21 Metso Fiber Karlstad Ab Metod för att återvinna värmeenergi från svartlut
KR20110123184A (ko) 2010-05-06 2011-11-14 바히아 스페셜티 셀룰로스 에스에이 높은 알파 용해 펄프 제조를 위한 방법 및 시스템
CN103757961B (zh) * 2013-12-30 2016-01-20 汶瑞机械(山东)有限公司 一种间歇蒸煮装置及其布液方法
US9644317B2 (en) 2014-11-26 2017-05-09 International Paper Company Continuous digester and feeding system
FI129440B (sv) * 2020-01-15 2022-02-28 Chempolis Oy Kokanordning och -förfarande för behandling av biomassa som innehåller lignocellulosa

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1687076A (en) * 1927-10-12 1928-10-09 Venning D Simons Process for cooking wood chips by the alkaline process of pulp manufacture

Family Cites Families (3)

* 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
JPS6059189A (ja) * 1983-08-24 1985-04-05 ベロイト　コ−ポレ−ション 多段式木材チツプ蒸解法
SU1498857A1 (ru) * 1987-07-17 1989-08-07 Сибирский научно-исследовательский институт целлюлозы и картона Способ щелочной варки целлюлозы в котлах периодического действи

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1687076A (en) * 1927-10-12 1928-10-09 Venning D Simons Process for cooking wood chips by the alkaline process of pulp manufacture

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Publication number Publication date
FI963448L (sv) 1996-09-03
FI118348B (sv) 2007-10-15
RU2127342C1 (ru) 1999-03-10
DE69505503D1 (de) 1998-11-26
PL316144A1 (en) 1996-12-23
EP0748412A1 (en) 1996-12-18
AU1978995A (en) 1995-09-18
BR9506974A (pt) 1997-09-16
NZ282616A (en) 1997-05-26
CN1143398A (zh) 1997-02-19
MX9603876A (es) 1997-03-29
DE69505503T2 (de) 1999-10-21
JP2876428B2 (ja) 1999-03-31
RO117929B1 (ro) 2002-09-30
TW270159B (sv) 1996-02-11
FI963448A0 (sv) 1996-09-03
CA2184706C (en) 2001-10-30
ATE172503T1 (de) 1998-11-15
CA2184706A1 (en) 1995-09-08
NO963520L (no) 1996-08-23
ES2126263T3 (es) 1999-03-16
ZA951777B (en) 1995-12-11
AU684623B2 (en) 1997-12-18
WO1995023891A1 (en) 1995-09-08
JPH09505115A (ja) 1997-05-20

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