EP3464715B1 - Verfahren zur herstellung von zellstoff in einer aufschlussanlage einer zellstofffabrik - Google Patents

Verfahren zur herstellung von zellstoff in einer aufschlussanlage einer zellstofffabrik Download PDF

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Publication number
EP3464715B1
EP3464715B1 EP17739623.1A EP17739623A EP3464715B1 EP 3464715 B1 EP3464715 B1 EP 3464715B1 EP 17739623 A EP17739623 A EP 17739623A EP 3464715 B1 EP3464715 B1 EP 3464715B1
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Prior art keywords
black liquor
steam
digester
flashing
heat exchanger
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EP17739623.1A
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English (en)
French (fr)
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EP3464715A1 (de
Inventor
Auvo Kettunen
Johan ENGSTRÖM
Jussi Piira
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Andritz Oy
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Andritz Oy
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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
    • D21C7/00—Digesters
    • D21C7/10—Heating devices
    • 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
    • D21C3/24—Continuous 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
    • D21C7/14—Means for circulating the lye

Definitions

  • the present invention relates to a method and an arrangement for producing chemical pulp at a continuous digester plant of a chemical pulp mill.
  • Prior art utilizes a fiberline system with a chip bin, where wood chips or other cellulosic material is steamed and liquid is admixed therein for forming a slurry, after which the slurry is pressurized (this section is also referred to as a feed system), fed into a treatment vessel or treatment vessels (which may be an impregnation vessel, a pre-hydrolysis process or other vessels), whereafter follows a digester.
  • a treatment vessel or treatment vessels which may be an impregnation vessel, a pre-hydrolysis process or other vessels
  • a digester At present, at least one black liquor stream is extracted from the cooking system (typically at a temperature of 120-180°C).
  • the extracted black liquor stream or streams can be used as a heat source for preheating white liquor, other black liquor streams and/or other liquid streams being led to feed and cooking systems.
  • the extracted black liquor stream (or streams) can then be led to a pre-evaporation system, i.e. to one or several flash tanks, wherein steam is generated from hot black liquor as it is cooled, typically to a temperature of approximately 105-125 °C. After optional additional cooling to 90-95 °C the black liquor is led to an evaporator system of the recovery zone.
  • a pre-evaporation system i.e. to one or several flash tanks, wherein steam is generated from hot black liquor as it is cooled, typically to a temperature of approximately 105-125 °C.
  • the black liquor is led to an evaporator system of the recovery zone.
  • the thus generated flash steam can be used at another location in the pulping process. Flash steam can e.g. be used for direct preheating of chips prior to cooking.
  • the above described flashing process has the disadvantage that the generated steam contains volatile compounds, including sulfur compounds, which are not desirable in wood chip presteaming.
  • wood chips are steamed at atmospheric or slightly higher pressure so that residual gases are not absorbed into the wood chips, but they are collected and treated.
  • the treatment is typically combustion in the non-condensable gas (NCG) system of the mill.
  • NCG non-condensable gas
  • This collection and treatment system becomes especially significant when the used steam contains volatile compounds, including sulfur compounds, which have a disadvantageous impact for the environment, including detrimental odor. Therefore, it is advantageous to use such a heat source that minimizes or eliminates the introduction of volatile compounds into the steaming process.
  • an explosion risk exists, if concentrated gases entrained in flash steam are introduced into low concentration gases. Therefore, it is advantageous to find for flash steam other objects of use than pretreatment, such a steaming, of cellulosic material being fed into digestion.
  • US-patent 6,722,130 discloses a system for producing clean steam from black liquor. First the pressure of the black liquor is decreased for producing a second black liquor having a higher concentration and black liquor vapor, which is condensed to condensate. This condensate is heated with the first black liquor and steam-flashed for producing clean steam to be used in a chip bin.
  • WO 2007073333 discloses a system and a method for producing steam at a digester plant of a chemical pulp mill.
  • the pressure of hot pressurized black liquor obtained from a digester is decreased in a first stage for producing black liquor steam that is used for chip pretreatment in a second preheating stage.
  • Clean steam for pretreating chips in the first preheating stage is generated by re-heating the black liquor, the pressure of which was decreased prior to the final subsequent pressure decrease, where the increased black liquor steam volume is led into a steam converter for producing clean steam.
  • US 2010/0236733 A1 relates to a method for generating steam in a digester plant of a chemical pulp mill, which includes the generation of vapor from black liquor by evaporating the black liquor due to heating with fresh steam.
  • WO 2008/057040 A1 describes a method of producing cellulose pulp in a continuous digester system, wherein black liquor is withdrawn from the digester vessel and led to the bottom of an impregnation vessel containing impregnated chips and impregnation fluid.
  • US 2010/0224335 A1 relates to a method for heating (a mixture of) white liquor for use in a digester system of a chemical pulp mill, wherein black liquor extracted from the digester system is flashed to generate flash vapor that is then directed through a heat exchanger to heat a white liquor.
  • WO-A1-00/11263 discloses a method of producing chemical pulp in a continuous digester plant according to the preamble of claim 1.
  • An object of the present invention is to avoid the above mentioned problems and to provide an improved and alternative method of heating fibrous material at the top of the digester by utilizing the heat of black liquor as efficiently as possible.
  • One object is also to improve the overall energy economy of a chemical pulp mill.
  • Another object is to utilize flash steam of the black liquor at a location that is advantageous in view of its composition.
  • the present invention provides a new method, in which the use of live steam for heating fibrous material in a digester can be decreased.
  • the new method comprises the following steps:
  • the method comprises a step, wherein the flashed black liquor from step c) is led into subsequent heat recovery stages, e.g. into a second flashing vessel, whereby a second flash steam and a second flashed black liquor are generated.
  • Heat can be recovered from the flashed black liquor also or alternatively e.g. in a kettle reboiler or in a black liquor cooler.
  • the first mentioned allows to produce as known per se steam from a clean liquid for pretreating fibrous material and the latter allows heating water fractions of the mill.
  • a central feature of the new method is that extraction liquor from the digester is led through an indirect heat exchanger, wherein its heat is increased with live steam, typically with intermediate pressure steam, the pressure of which is typically 6-17 bar (g).
  • live steam typically with intermediate pressure steam, the pressure of which is typically 6-17 bar (g).
  • intermediate pressure steam depending on its pressure, the temperature of the black liquor is typically increased into a level of approximately 160-190 °C, e.g. to 175-185 °C.
  • the invention is utilized in a vapor phase digester. At a higher temperature, more flash steam is obtained from the same amount of liquor, but then a larger heat exchange area is needed in the heat exchanger, which can increase the equipment costs. After this the heated black liquor is led into a flashing vessel, where it is allowed to flash into steam that is used at the top of the digester for heating the fibrous material instead of live steam.
  • the flashed black liquor can be led from the first flashing vessel into a subsequent flashing vessel, typically with other extraction liquor or other extraction liquors extracted from the digester, and the black liquor is flashed therein again.
  • the flash steam of this second flashing vessel can be used in a vapor reboiler for producing clean steam, which can be used for steaming the fibrous material, such as wood chips, prior to the digester.
  • Black liquor is extracted from the digester at one or several levels depending on the cooking process, e.g. between cooking and washing zones.
  • Extraction liquor from the digester which is heated in a heat exchanger, can be either upper extraction liquor, lower extraction liquor, or if e.g. there are several lower extraction screens, extraction liquor from the uppermost screen row.
  • Black liquor can be led into the heat exchanger also from two or more screen levels.
  • black liquor at the highest temperature is heated for optimizing the consumption of heating medium, steam, in the heat exchanger.
  • the temperature of the black liquor stream extracted from the digester is dependent on the cooking mode. If there are more than one black liquor stream, the black liquor that is extracted at the end of the cooking stage from the lower part of the digester typically has the highest temperature.
  • step b) at least two black liquor streams are extracted from the digester, which streams are at different temperatures.
  • the black liquor stream at a higher temperature is heated in the heat exchanger, and the second black liquor stream at a lower temperature is led to heat recovery, such as into a second heat exchanger or a second flashing vessel.
  • the present invention can be applied in connection with both a single vessel digester and a two-vessel digester.
  • the digester is a vapor phase digester, whereby the flash steam is led into a gas space at the top of the digester for heating the fibrous material.
  • the flash steam can also be fed into the upper part of a hydraulic digester with a steam injector, as described in WO-publication 2016/038251 .
  • An essential feature of the invention is heating of the extraction liquor with subsequent flashing, whereby the digester does not necessary need steam from outside the balance area, but the steam originates from internal circulation. Further, in an indirect heat exchanger the condensate of live steam can be recovered and led back to the boiler plant as boiler water.
  • Flashed liquor can also be recirculated back via the heat exchanger into a flashing vessel, whereby the amount of flash steam can be further increased.
  • a slurry formed of comminuted cellulosic fibrous material, such as wood chips, and liquid is led into the top of the digester 1 via line 2.
  • the slurry Prior to the digester the slurry can alternatively be fed for treatment into a treatment vessel or vessels (can be an impregnation vessel, pre-hydrolysis vessel or other vessels, not shown).
  • a treatment vessel or vessels can be an impregnation vessel, pre-hydrolysis vessel or other vessels, not shown).
  • the figure illustrates only those components that are important in view of the invention.
  • the digester is a vapor phase digester. Also steam is added to the top of the digester via line 3.
  • the digester 1 comprises at least one or more screen arrangements 4, 5 and 6, via which black liquor can be extracted.
  • Black liquor having a temperature of typically 120-180 °C and a dry solids content of 12-17 %, is extracted via a screen 4 and line 7 and led into a flashing vessel 9.
  • Line 7 is provided with a heat exchanger 8, in which the black liquor is heated indirectly with steam, typically medium pressure steam from line 24.
  • the black liquor has typically been pressurized in the digester to a pressure of 5 - 15 bar (abs) and its temperature corresponds to the temperature of cooking treatment (approximately 130 - 180 °C).
  • black liquor at the highest temperature is heated for optimizing the consumption of heating medium, steam, in the heat exchanger 8.
  • Live steam is condensed in the heat exchanger 8, and the thus generated live steam condensate in line 25 is clean.
  • the condensate can be led into a recovery boiler plant of the mill, where it can be used as feed water.
  • the pressure of the black liquor is decreased for producing flash steam and for producing flashed black liquor, the dry solids content of which typically increases in the flashing.
  • the construction of the flashing vessel 9 is substantially conventional and it has a feed line 10 for hot black liquor, an outlet 11 for flash-evaporated vapor, and an outlet 12 for cooled black liquor at a lower pressure. Flashing vessels are typically operated so that the pressure prevailing in them is lower than the pressure of black liquor led thereto, but higher than the pressure at the top of the digester, typically approximately 4-7 bar (abs).
  • Flashing vessels are containers designed for this purpose, which facilitate the pressure decrease of hot, pressurized black liquor, whereby liquid, typically water, is vaporized from the black liquor very quickly, into steam, whereby also the concentration of spent cooking chemical and the products of a cooking reaction (dissolved solids) is increased.
  • the steam produced in this quick evaporation is discharged via a steam discharge opening 11 into line 3 at a pressure prevailing in the vessel 9, e.g. 4-7 bar (abs) and at a saturation temperature corresponding to the prevailing pressure, e.g. approximately 140 - 180 °C.
  • the remaining liquid which typically also is at a temperature of approximately 160 °C settles onto the bottom of the vessel 9, from where it is discharged from an outlet 12 via line 13.
  • the flash steam from flashing vessel 9 is led via line 3 to the top of the digester 1 to be used as heating steam.
  • the temperature of the steam e.g. 140-180 °C,140-180 °C, is typically higher than the cooking temperature, so that the steam that is led via the steam inlet of the digester, which inlet is in contact with the flashing vessel, heats the fibrous material to the cooking temperature.
  • the flashed black liquor is led via line 13 to another flashing vessel 15 of the mill, where the black liquor is further flashed. A portion of the black liquor can be circulated via line 14 and heat exchanger 8 to flashing, and thus it is possible to further increase the amount of steam being generated in the flashing vessel 9.
  • Black liquor is supplied into the second flashing vessel 15 also from the digester from digester screens, in this case from washing screen 6 via line 16.
  • the liquid remaining after the flashing which typically is at a temperature of approximately 100 - 140 °C, settles on the bottom of vessel 15, from where it is discharged via line 17.
  • the discharge line 17 can be provided with a black liquor cooler 18, in which heat can be recovered from the black liquor.
  • water in line 26 is typically heated for producing hot water, which discharges via line 28.
  • the flashed, cooled black liquor is led via line 27 to the evaporation plant of the mill, where the black liquor is concentrated to a high solids content prior to combustion in a recovery boiler.
  • the flash steam from the second flashing vessel 15 is led via line 19 into a reboiler 20, wherein the energy contained therein is recovered.
  • the steam is set in an indirect heat exchange contact with "clean" liquid free of volatile compounds for heating the liquid to a temperature exceeding the boiling temperature for producing clean steam.
  • the reboiler is preferably a falling film tube reboiler. Flash steam is condensed inside the tubes, while clean liquid boils on the outer surface of the tubes for producing clean steam.
  • Clean steam in line 22 is typically used for pretreating the fibrous material to be fed into the digester, such as for steaming wood chips.
  • the clean liquid is led via line 21 into the reboiler 20. It can typically comprise condensate from an evaporator, demineralized water, or adequately clean water fraction, such as e.g. hot water of the mill.
  • the clean steam produced in the reboiler contains a substantially smaller amount of non-condensible gases than steam produced by direct flashing of black liquor.
  • Clean steam in line 22 is preferably used for wood chips preheating by means of steam. Flash steam from the black liquor flashing vessel 15 contains volatile compounds, such a sulfur compounds. These compounds enter the foul condensate and into the stream of concentrated non-condensible gases, CNCG, generated in the reboiler.
  • the foul condensate is sent from the reboiler via line 23 to the evaporation plant where it is treated in a manner known per se. Heat can be recovered from the flashed black liquor exiting from the first flashing vessel also in other ways than additional flashing.
  • the produced pulp is discharged from the bottom of the digester via line 29.
  • FIG 2 illustrates an alternative solution for leading black liquor from the digester into the first flashing vessel 9.
  • black liquor is led into the first flashing vessel also from a second screen.
  • the digester screen 6 comprises two screen levels 6a and 6b.
  • black liquor is extracted via the upper screen row 6a into line 30 and via line 31 further into the flashing vessel 9.
  • the temperature of this black liquor stream can be already adequately high so that it does not need heating prior to flashing.
  • the black liquor stream is led into heat exchanger 8 via lines 30 and 32.
  • black liquor is extracted via line 33 to heat recovery, e.g. flashing.
  • the extraction liquor fraction taken from the end of the cook is divided by means of two separate screens into two streams.
  • the amount of one of the streams is e.g. 3,0 m 3 /adt at a temperature of 169 °C and the amount of the other stream is 2,5 m 3 /adt at a temperature of 120 °C.
  • the cooler stream of these is taken to conventional heat recovery.
  • the hotter stream is taken into a heat exchanger, where it is heated indirectly with intermediate pressure steam to a temperature of 180 °C, whereby steam is consumed in the amount of approximately 50 kg/adt.
  • the heated liquor is taken into a flash tank, where the pressure of the liquor decreases to a pressure of 4,5 bar(g) and the temperature to a level of 158 °C.
  • flash steam is generated in the amount of approximately 110 kg/adt, which is taken to the top of the digester, where the pressure level is approximately 4 bar(g).
  • the solution according to the invention provides a saving of 110 kg/adt of direct intermediate pressure steam at the top of the digester by using 50 kg/adt of indirect intermediate pressure steam in the heat exchanger.
  • black liquor is evaporated by 100 kg/adt reducing the evaporation need of the evaporation plant and hot condensate of intermediate pressure steam is recovered 50 kg/adt.

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Claims (6)

  1. Verfahren zum Herstellen von Zellstoff in einer kontinuierlichen Zellstoffkocheranlage, wobei das Verfahren die folgenden Schritte umfasst:
    a) Leiten einer aus zerkleinertem zellulosehaltigem Fasermaterial und Flüssigkeit gebildeten Aufschlämmung in einen Zellstoffkocher (1) und Behandeln des Materials mit einer Behandlungschemikalie bei einer Temperatur von über 130 °C zum Herstellen von behandeltem Material und Schwarzlauge;
    b) Abziehen mindestens eines Schwarzlaugestroms aus dem Zellstoffkocher (1) und Leiten der Schwarzlauge in eine indirekte Wärmetauschbeziehung mit Dampf in einem Wärmetauscher (8), um die Schwarzlauge zu erwärmen; und
    c) Leiten der erwärmten Schwarzlauge in einen Entspannungskessel (9), wobei entspannter Dampf und entspannte Schwarzlauge erzeugt werden,
    gekennzeichnet durch den Schritt des
    d) Verwendens von entspanntem Dampf aus Schritt c), zum Erwärmen des Fasermaterials in dem Zellstoffkocher (1) in Schritt a).
  2. Verfahren nach Anspruch 1, wobei ein zweiter Schwarzlaugestrom aus dem Zellstoffkocher (1) abgezogen wird, und der zweite Schwarzlaugestrom vor dem Wärmetauscher (8) in Schritt b) mit dem ersten Schwarzlaugestrom vereinigt wird.
  3. Verfahren nach Anspruch 1 oder 2, wobei in Schritt b) Frischdampf verwendet wird, bei dem es sich um Zwischendruckdampf handelt, der einen Druck von 6-17 bar (g) aufweist.
  4. Verfahren nach Anspruch 1, 2 oder 3, wobei die entspannte Schwarzlauge aus Schritt c) in einen zweiten Entspannungskessel (9) geleitet wird, wobei ein zweiter entspannter Dampf und eine zweite entspannte Schwarzlauge erzeugt werden.
  5. Verfahren nach einem der vorstehenden Ansprüche, wobei entspannte Schwarzlauge aus dem ersten Entspannungskessel (9) mittels des Wärmetauschers (8) zum Entspannen zurück zirkuliert wird.
  6. Verfahren nach einem der vorstehenden Ansprüche, wobei in Schritt b) mindestens zwei Schwarzlaugeströme bei unterschiedlichen Temperaturen aus dem Zellstoffkocher (1) abgezogen werden, und der Schwarzlaugestrom bei einer höheren Temperatur in dem Wärmetauscher (8) erwärmt wird, und der zweite Schwarzlaugestrom bei einer niedrigeren Temperatur zur Wärmerückgewinnung geleitet wird.
EP17739623.1A 2016-06-06 2017-06-01 Verfahren zur herstellung von zellstoff in einer aufschlussanlage einer zellstofffabrik Active EP3464715B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20165470A FI20165470A (fi) 2016-06-06 2016-06-06 Menetelmä kemiallisen massan tuottamiseksi sellutehtaan keittämöllä
PCT/FI2017/050408 WO2017212111A1 (en) 2016-06-06 2017-06-01 Method of producing chemical pulp at a digester plant of a chemical pulp mill

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Publication Number Publication Date
EP3464715A1 EP3464715A1 (de) 2019-04-10
EP3464715B1 true EP3464715B1 (de) 2021-07-28

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EP17739623.1A Active EP3464715B1 (de) 2016-06-06 2017-06-01 Verfahren zur herstellung von zellstoff in einer aufschlussanlage einer zellstofffabrik

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EP (1) EP3464715B1 (de)
ES (1) ES2896078T3 (de)
FI (1) FI20165470A (de)
PT (1) PT3464715T (de)
UY (1) UY37275A (de)
WO (1) WO2017212111A1 (de)

Families Citing this family (1)

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Publication number Priority date Publication date Assignee Title
SE544629C2 (en) * 2021-02-03 2022-09-27 Valmet Oy Indirect heating of digester

Citations (7)

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Publication number Priority date Publication date Assignee Title
US3258390A (en) 1962-10-20 1966-06-28 Domtar Ltd Method and apparatus for maintaining a water balance during impregnation and digestion of cellulosic material
DE3621120A1 (de) 1985-07-02 1987-01-15 Kamyr Ab Verfahren zur behandlung von zellulosematerial in einem dampf-fluessigkeits-phasen-kocher
US6306252B1 (en) 1995-04-10 2001-10-23 Andritz-Ahlstrom Inc. Heat recovery from spent digester cooking liquor
US20100224335A1 (en) 2009-03-05 2010-09-09 Andritz Inc. Heat recovery from spent cooking liquor in a digester plant of a chemical pulp mill
US20100236733A1 (en) 2009-02-09 2010-09-23 Andritz Inc. Method and system to generate steam in a digester plant of a chemical pulp mill
WO2015132469A1 (en) 2014-03-05 2015-09-11 Andritz Oy Method and arrangement for generating steam at a digester plant of a chemical pulp mill
US20150284909A1 (en) 2012-02-13 2015-10-08 Andritz Inc. Flash tank with adjustable inlet and method for adjusting inlet flow to a flash tank

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Publication number Priority date Publication date Assignee Title
US6176971B1 (en) * 1998-11-18 2001-01-23 Andritz-Ahlstrom Inc. Heat economy enhancements for the recovery and use of energy obtained from spent cooking liquors
SE0602349L (sv) * 2006-11-07 2008-05-06 Metso Fiber Karlstad Ab Förfarande för att energieffektivt producera cellulosamassa i ett kontinuerligt kokeri

Patent Citations (7)

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Publication number Priority date Publication date Assignee Title
US3258390A (en) 1962-10-20 1966-06-28 Domtar Ltd Method and apparatus for maintaining a water balance during impregnation and digestion of cellulosic material
DE3621120A1 (de) 1985-07-02 1987-01-15 Kamyr Ab Verfahren zur behandlung von zellulosematerial in einem dampf-fluessigkeits-phasen-kocher
US6306252B1 (en) 1995-04-10 2001-10-23 Andritz-Ahlstrom Inc. Heat recovery from spent digester cooking liquor
US20100236733A1 (en) 2009-02-09 2010-09-23 Andritz Inc. Method and system to generate steam in a digester plant of a chemical pulp mill
US20100224335A1 (en) 2009-03-05 2010-09-09 Andritz Inc. Heat recovery from spent cooking liquor in a digester plant of a chemical pulp mill
US20150284909A1 (en) 2012-02-13 2015-10-08 Andritz Inc. Flash tank with adjustable inlet and method for adjusting inlet flow to a flash tank
WO2015132469A1 (en) 2014-03-05 2015-09-11 Andritz Oy Method and arrangement for generating steam at a digester plant of a chemical pulp mill

Non-Patent Citations (1)

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Title
CRESLOW PUSTELNIK ET AL.: "The Mechanical-Chemical Pulping of Straw According to the Aronovsky Method", DEPARTMENT OF AGRICULTURE AND THE NATIONAL SCIENCE FOUNDATION, 1964, pages 1 - 40, XP055919060

Also Published As

Publication number Publication date
PT3464715T (pt) 2021-11-02
FI20165470A (fi) 2017-12-07
UY37275A (es) 2018-01-31
WO2017212111A1 (en) 2017-12-14
ES2896078T3 (es) 2022-02-23
EP3464715A1 (de) 2019-04-10

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