WO2019039982A1 - Procédé compact amélioré pour la production d'une pâte préhydrolysée - Google Patents

Procédé compact amélioré pour la production d'une pâte préhydrolysée Download PDF

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Publication number
WO2019039982A1
WO2019039982A1 PCT/SE2018/050738 SE2018050738W WO2019039982A1 WO 2019039982 A1 WO2019039982 A1 WO 2019039982A1 SE 2018050738 W SE2018050738 W SE 2018050738W WO 2019039982 A1 WO2019039982 A1 WO 2019039982A1
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WO
WIPO (PCT)
Prior art keywords
prehydrolysis
neutralized
digester
temperature
slurry
Prior art date
Application number
PCT/SE2018/050738
Other languages
English (en)
Inventor
Fredrik Wilgotson
Stefan ANTONSSON
Original Assignee
Valmet Ab
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 Valmet Ab filed Critical Valmet Ab
Priority to BR112020003285-9A priority Critical patent/BR112020003285A2/pt
Priority to EP18847479.5A priority patent/EP3673110A4/fr
Publication of WO2019039982A1 publication Critical patent/WO2019039982A1/fr

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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
    • D21C1/02—Pretreatment of the finely-divided materials before digesting with water or steam
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C1/00—Pretreatment of the finely-divided materials before digesting
    • D21C1/04—Pretreatment of the finely-divided materials before digesting with acid 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
    • D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes

Definitions

  • the present invention relates to a process for production of pulp in which hemicellulose is hydrolyzed into hydrolysate, and lignin is dissolved by a kraft cooking method for liberating cellulose fibers. Still more particularly, the present invention relates to a process for production of a pulp which has a high content of alpha cellulose and can be sold as dissolving pulp.
  • a separate prehydrolysis step permits the desired adjustment of the hydrolysis of hemicelluloses by varying the hydrolysis conditions.
  • the bulk delignification is not carried out until a separate alkaline cooking step, even though some handbooks indicate that as much as 30 kg of lignin per ton of wood may be dissolved in the prehydrolysis (i.e. a small part of the total lignin content as 30 kg per ton of wood corresponds to some 3 % of the wood material).
  • the conditions for prehydrolysis is most often established by heating in a hot steam phase or hot water liquid environment, where the natural wood acidity released will usually lower the pH down to about 3.5, most often referred to as autohydrolysis. Sometimes could also additional acid and a catalyst be added.
  • the subsequent delignification step has been a conventional kraft cooking method, where white liquor has been added to the digester.
  • US 8,734,610 is disclosed a two-vessel digester system, where the acidic hydrolysis is established in an upper half of a first prehydrolysis vessel, followed by a countercurrent water- wash stage with some alkali addition.
  • This system is of similar design as the old Varkaus (Finland) digester system that had the inherent pitch problems in the screen section ending the hydrolysis zone, and this system could only be operated in short campaigns with dissolving pulp production, said campaign being maximized to about two weeks at the most, requiring a swing production to standard kraft pulping process after these two weeks.
  • the old Varkaus system is described in detail in US 4,436,586 (1984).
  • the pitch problem is partially solved by the fact that the strainers in the batch digester are switching from withdrawing acidic prehydrolysate to alkaline cooking liquor and later on black liquor.
  • the volume of acidic hydrolysate withdrawn after a steam phase prehydrolysis is also relatively small in total volume so the exposure in strainers is limited.
  • the latter alkaline stages will then also dissolve and wash out any pitch deposits such that they do not build up over time. This is not possible to achieve in continuous systems as the strainers are located in a stationary process position where the chemical conditions (as of pH, pitch content, etc.) do not change.
  • the hydrolysis step is conducted in a steam phase, can the following neutralization and alkalization of the wood material be obtained rather quickly and thoroughly as the wood material has been steamed at high temperature in a steam phase, allowing the alkali to penetrate the wood material by diffusion.
  • this type of well-defined transition zone between the prehydrolyse in a steam phase and the neutralization is not favorable in a continuous system where the wood material is supposed to flow through reaction towers in a plug flow.
  • the hydrolysis is instead most often implemented in a liquid filled stage at least in final parts.
  • dissolving pulp for such end uses as spinning fibers is considered to be an optional method for producing textiles having less environmental impact compared with production of cotton textiles.
  • the interest for dissolving pulp increases in years when cotton production is low due to crop failure.
  • Dissolving pulp is also a base product for different additives and consistency agents and fillers in tyre cord and casings, ether and spongs, nitrocellulose and acetate.
  • dissolving pulps may be an alternative product instead of pulp for regular paper pulp making.
  • a common implementation in most prehydrolysis-kraft cooking processes is that the prehydrolysis stage has been terminated by withdrawal of the prehydrolysate, either in form of a pure acidic prehydrolysate, or in form of a neutralized prehydrolysate. As indicated before would any strainers in such process position be subjected to pitch deposits, both when the prehydrolysate is kept at its lowest pH level or if the prehydrolysate is withdrawn in a transition position where the chip suspension switch from acidic to alkaline.
  • WO 2012158075 Metalso Paper Sweden which now is Valmet AB
  • a first embodiment is a three-vessel design proposed, where an intermediate alkaline extraction process is established after the first hydrolysis vessel, enabling a further extraction of both hemicellulose and lignin from the hydrolysed cellulosic slurry.
  • a second embodiment is a two-vessel design proposed where the charge of colder alkali is added to the end of the first hydrolysis vessel, and a first withdrawal to recovery is made in a digester screen section.
  • the inventive concept is based on a moderate alkalizate ion of the hydrolysed cellulosic slurry and using mixing effects of process components in the transfer system to a subsequent digester before a first withdrawal of hydrolysis liquid in a top separator and within a very short time frame less than 10 minutes after alkali addition.
  • BS bottom scraper
  • the neutralized slurry maintained for a short time not exceeding 5 minutes, preferably in the range of 1 -2 minutes, in the neutralized state before extraction from the top separator.
  • the neutralizing alkali charge can contain at least one of fresh white liquor, extracted black liquor from a digester, or alkaline wash liquor from subsequent digester or alkaline pre-bleaching.
  • the neutralizing alkali charge can be added in such amount and at such temperature that the resulting temperature of the neutralized slurry is lowered by at least 10 % in comparison to the temperature in the prehydrolysis stage, preferably at least 12 °C if the prehydrolyse temperature is about 120 °C, and at least 18 °C if the prehydrolyse temperature is about 180 °C.
  • a substantial reduction in temperature will effectively end the prehydrolysis of the cellulose material, in combination with the swing to moderate alkaline conditions, i.e. 5-10 g/l.
  • the resulting temperature is the same as the temperature to be established in the subsequent digester, reducing need to add steam to digester top for heating.
  • the neutralization stage is kept short, i.e. less than 10 minutes, this also implies that the alkali concentration established cannot be subjected to any larger order of alkali consumption during delignification reaction processes, which forms the very foundation for keeping the alkalization in the neutralization at a moderate level and not risking the concentration to drop so much that pitch deposits are formed on screens in subsequent withdrawal.
  • additional alkaline liquors can be added to the feeding line ahead of top separator, said additional alkaline liquors added in an amount sufficient for establishing a L/W ratio sufficient for maintaining the withdrawal capacity in the top separator and a high extraction volume sent to recovery in return line from the top separator, thereby avoiding top separator plugging.
  • the top separator needs to be operated with a certain overflow of liquor, as high degree of drainage of liquid in the withdrawal compartment, lowering the liquid level, may drain the plug of cellulose material excessively, and thus may form a plug that may activate the overload stop in the drive of the top separator motor. Adding additional liquid to the feeding line may quickly control the liquid overflow of the top separator, and maintain the withdrawal capacity high.
  • the slurry after the addition of neutralizing alkali charge can be subjected to mechanical agitation first from a bottom scraper and finally from a top separator having a feeding screw sweeping over withdrawal screens.
  • These components add a mixing effect into the neutralized slurry and guarantee that the alkali concentration is established evenly throughout the entire volume of the neutralized slurry, thus reducing pitch deposits forming on top separator screen.
  • the slurry after the addition of neutralizing alkali charge be subjected to mechanical agitation from a pump located in the feeding line to the top of a kraft cooking digester. This pump can in some systems be discarded as the pressure in the outlet from the prehydrolyzing vessel often is sufficient for establishing a flow in the feeding line.
  • the inventive process can be implemented in any type of prehydrolysis stage, such as a one where the acidification of said prehydrolysis is established only by steam heating and optionally adding water, and without adding any external acidifiers, only using the wood acidity released during steam heating reaching a pH level below 5 during the prehydrolysis. It can also be implemented in one where the acidification of said prehydrolysis is established in a liquid-filled phase wherein the acidification of said prehydrolysis is established by heating and addition of external acidifiers, reaching a pH level below 3 during the prehydrolysis established in a liquid- filled phase. Finally, the inventive process can be implemented in a continuous digester system using one vessel for the prehydrolysis and one vessel for an alkaline pre-extraction stage and the kraft cooking stage.
  • the lignin-containing cellulosic materials to be used in the present process are suitably softwood, hardwood, or annual plants. According to the present invention, prehydrolysis-kraft pulp can be obtained with a high yield of alpha cellulose with a high polymerization degree.
  • Fig. 1 is a schematic representation of the prehydrolysis-kraft cooking process according to US 5,589,033;
  • Fig. 2 is a schematic representation of the of the prehydrolysis-kraft cooking process according to WO 2012158075;
  • Fig. 3 is a schematic representation of the cooking process according to the invention.
  • Fig. 4 shows a principal set up for a continuous cooking system using the inventive process, here using a prehydrolysis tower and one subsequent vessels for alkaline treatment and cook.
  • Fig. 1 shown the cooking steps of US 5,589,033.
  • the chips are first treated in the prehydrolysis step Pr, where chips are heated by steam to 170 °C for 25 minutes. Thereafter is heated white liquor added in order to establish a neutralization step Ne, and the acidic prehydrolysate RECAc is withdrawn from the process.
  • the neutralization step is established at 155 °C for 15 minutes. Even though the white liquor is heated, the temperature is decreased by some 8 %.
  • the neutralization liquid is displaced by adding hot black liquor BLHOT, and this establishes an alkaline black liquor impregnation step BL held at 148 °C for 20 minutes.
  • the black liquor is withdrawn, and a new charge of white liquor is added ahead of the following cooking step Co, which is held at 160 °C for 54 minutes.
  • the white liquor used is heated both in a heat exchange with hot spent cooking liquor as well as steam in order not keep the temperature at high level, before being used as the neutralizing liquid.
  • Fig. 2 shows the cooking steps of WO 2012158075.
  • a first steaming step ST for the chips this step may be avoided of the subsequent prehydrolysis is implemented in a steam phase.
  • the chips are thereafter treated in the prehydrolysis step Pr, where chips are heated by steam at a temperature of between about 120 °C and 180 °C and during at least 20 minutes, to produce a prehydrolyzed cellulosic material and an acidic hydrolysate.
  • Addition of liquid, such as water H2O is an option, which may be preferable if a liquid prehydrolysis is sought for, for example in a continuous cooking system.
  • Another option is to add an acidifier Ac, if a lower temperature is sought for in the prehydrolysis.
  • a first steaming step ST for the chips is shown a first steaming step ST for the chips but this step can be avoided if the subsequent prehydrolysis is implemented in a steam phase.
  • the chips are thereafter treated in the prehydrolysis step Pr, where chips are heated by steam at a temperature of between about 120 °Cand 180 °C and during at least 20 minutes, to produce a prehydrolyzed cellulosic material and an acidic hydrolysate.
  • Addition of liquid, such as water H2O is an option, which can be preferable if a liquid prehydrolysis is sought for, for example in a continuous cooking system.
  • Another option is to add an acidifier Ac if a lower temperature is sought for in the prehydrolysis.
  • the novel approach disclosed in this figure is the usage of the transfer circulation Tr as the position for first withdrawal of dissolved matter from the hydrolysis stage.
  • the residence time for the hydrolysed slurry in the transfer circulation is typically within 1-3 minutes, and well below 10 minutes.
  • a moderate alkali charge AL added to the hydrolysed slurry.
  • the inventive process is a distinct ending of the prehydrolysis implemented by adding a moderate alkali charge AL with a volume and at a temperature that will reduce the temperature of the cellulosic material by at least 10 % in comparison to the temperature in the prehydrolysis stage, preferably at least 12 °C if the prehydrolyse temperature is about 120 °C and at least 18 °C if the prehydrolyse temperature is about 180 °C.
  • This will establish an alkaline treatment liquor which after this charge establishes an effective alkali concentration in the range 5-10 g/l EA as NaOH.
  • the neutralized slurry is withdrawn within a short period of time less than 10 minutes and preferably within 1-3 minutes while having been subjected to mechanical mixing effects from at least a bottom scraper and a top separator screw.
  • the short retention time in the transfer system Tr guarantees that no major consumption of alkali is established, which is the basis for keeping the charge of alkali at relatively modest level.
  • the charge of fresh alkali i.e. typically in form of concentrated white liquor directly from the white liquor preparation in the causticizing area can thus be reduced, and to some extent be replaced by alkaline filtrates from brown wash (wash directly after digester or after a first oxygen delignification stage) or black liquor extraction flows from digester.
  • the cellulosic material is transferred from the transfer system to a kraft cooking stage Co.
  • the kraft cook can be implemented in any kind of known kraft cooking method continuous cooking such as, Compact Cooking, Lo-Solids cooking, ITC-cooking, MCC cooking, EAPC cooking as examples.
  • the kraft cook is then finished by a wash stage Wa, which can be implemented in any kind of known wash equipment, such as a countercurrent wash zone in bottom of a digester or using a pressure diffuser 40 wash, wash press or filter wash after
  • Fig. 4 a two-vessel continuous cooking system for prehydrolysis and cooking, wherein the inventive process is implemented.
  • the chips are first fed to a chip bin 1 and subsequent steaming vessel 2 during addition of steam ST for purging the chips from bound air.
  • the steamed chips fall into a liquid-filled chute above a high- pressure sluice feeder 3, which pressurize the steamed chips and feed the formed slurry of chips in a feed flow 4 to the prehydrolysis vessel 10.
  • the prehydrolysis vessel is in form of a steam-liquid phase digester having an inverted top separator 11 withdrawing a part of the transport liquid from line 4 back to start of feeding via A.
  • steam ST is added to top of vessel 10, and optionally can also acid be added from source Ac.
  • the moderate alkali charge added from any suitable source, such as extracted black liquor withdrawals from digester, REC2 and REC4, as well as alkaline wash filtrate (REC3) from a pressure diffuser wash 40 located directly after the digester.
  • the addition of the moderate alkali charge is done by mixing in the alkali to the return flow B.
  • the neutralized slurry is fed in line 14 to a steam-liquid phase digester 30, and excess transport fluid is withdrawn by an inverted top separator 31 and sent to B, which is added to bottom of the prehydrolysis vessel 10 as part of the transfer circulation. From the return flow a substantial part of the neutralizing liquor can be withdrawn.
  • the kraft cook is established in the digester 30 and finally the prehydrolysed and cooked pulp is washed in a pressure diffuser 40.

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Paper (AREA)

Abstract

L'invention concerne un procédé préhydrolyse-kraft dans lequel l'hydrolysat est extrait dans une position où la capacité d'extraction peut être obtenue sur une période de fonctionnement plus longue. Selon le procédé de l'invention, le premier volume d'hydrolysat est extrait du procédé après une alcalinisation modérée à la fin de l'hydrolyse (PR) et dans un délai inférieur à 10 minutes. Les effets de l'agitation mécanique et du mélange dans le système de transfert (TR) empêchent les dépôts de poix et les colmatages dans l'écran de séparation supérieur (31).
PCT/SE2018/050738 2017-08-25 2018-07-05 Procédé compact amélioré pour la production d'une pâte préhydrolysée WO2019039982A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
BR112020003285-9A BR112020003285A2 (pt) 2017-08-25 2018-07-05 processo para a preparação de polpa a partir de material celulósico contendo lignina
EP18847479.5A EP3673110A4 (fr) 2017-08-25 2018-07-05 Procédé compact amélioré pour la production d'une pâte préhydrolysée

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE1751023-1 2017-08-25
SE1751023 2017-08-25

Publications (1)

Publication Number Publication Date
WO2019039982A1 true WO2019039982A1 (fr) 2019-02-28

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PCT/SE2018/050738 WO2019039982A1 (fr) 2017-08-25 2018-07-05 Procédé compact amélioré pour la production d'une pâte préhydrolysée

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EP (1) EP3673110A4 (fr)
BR (1) BR112020003285A2 (fr)
WO (1) WO2019039982A1 (fr)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4174997A (en) * 1973-09-03 1979-11-20 Kamyr Aktiebolag Method and apparatus for continuous hydrolysis of cellulosic fiber material
JPS58126387A (ja) * 1982-01-22 1983-07-27 カムヤ−・インコ−ポレ−テツド 炭水化物材料およびクラフトパルプの製造方法
WO1995020065A1 (fr) * 1994-01-24 1995-07-27 Sunds Defibrator Pori Oy Production de pate prehydrolysee
WO2009116943A1 (fr) * 2008-03-20 2009-09-24 Metso Fiber Karlstad Ab Système d'alimentation comportant des pompes parallèles pour un digesteur continu
WO2012158075A1 (fr) * 2011-05-13 2012-11-22 Metso Paper Sweden Ab Procédé compact d'obtention de pâte préalablement hydrolysée

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT398588B (de) * 1992-12-02 1994-12-27 Voest Alpine Ind Anlagen Verfahren zur herstellung von viskosezellstoffen
FI20085425L (fi) * 2008-05-08 2009-11-09 Metso Paper Inc Sulfaattiesihydrolyysikeittomenetelmä
US9371612B2 (en) * 2011-02-22 2016-06-21 Andritz Inc. Method and apparatus to produce pulp using pre-hydrolysis and Kraft cooking
CN102493257B (zh) * 2011-12-07 2013-06-05 湖南骏泰浆纸有限责任公司 一种马尾松溶解浆及其生产方法

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4174997A (en) * 1973-09-03 1979-11-20 Kamyr Aktiebolag Method and apparatus for continuous hydrolysis of cellulosic fiber material
JPS58126387A (ja) * 1982-01-22 1983-07-27 カムヤ−・インコ−ポレ−テツド 炭水化物材料およびクラフトパルプの製造方法
US4436586A (en) * 1982-01-22 1984-03-13 Kamyr, Inc. Method of producing kraft pulp using an acid prehydrolysis and pre-extraction
WO1995020065A1 (fr) * 1994-01-24 1995-07-27 Sunds Defibrator Pori Oy Production de pate prehydrolysee
WO2009116943A1 (fr) * 2008-03-20 2009-09-24 Metso Fiber Karlstad Ab Système d'alimentation comportant des pompes parallèles pour un digesteur continu
WO2012158075A1 (fr) * 2011-05-13 2012-11-22 Metso Paper Sweden Ab Procédé compact d'obtention de pâte préalablement hydrolysée

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP3673110A4 *

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Publication number Publication date
EP3673110A1 (fr) 2020-07-01
BR112020003285A2 (pt) 2020-09-01
EP3673110A4 (fr) 2021-05-12

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