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WO2000011263A1 - Procede de prevention de l'incrustation - Google Patents

Procede de prevention de l'incrustation Download PDF

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Publication number
WO2000011263A1
WO2000011263A1 PCT/FI1999/000689 FI9900689W WO0011263A1 WO 2000011263 A1 WO2000011263 A1 WO 2000011263A1 FI 9900689 W FI9900689 W FI 9900689W WO 0011263 A1 WO0011263 A1 WO 0011263A1
Authority
WO
WIPO (PCT)
Prior art keywords
waste liquor
temperature
liquor flow
flow
liquor
Prior art date
Application number
PCT/FI1999/000689
Other languages
English (en)
Inventor
Kaj Henricson
Erkki KIISKILÄ
Original Assignee
Andritz-Ahlstrom 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 Andritz-Ahlstrom Oy filed Critical Andritz-Ahlstrom Oy
Publication of WO2000011263A1 publication Critical patent/WO2000011263A1/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
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/22—Other features of pulping processes
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • 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
    • D21C11/10—Concentrating spent liquor by evaporation
    • D21C11/106—Prevention of incrustations on heating surfaces during the concentration, e.g. by elimination of the scale-forming substances contained in the liquors

Definitions

  • the present invention relates to a method of preventing scale formation in a pulping process of chemical pulp.
  • Alkaline digestion, sulfate process in particular has traditionally been carried out by mixing cellulosic material, e.g. wood chips, with cooking liquor into a digestion vessel, the temperature of which is then elevated for a certain period of time to a digestion temperature, typically to 160-180°C, whereby lignin is separated from the wood material and, as a result, chemical pulp and waste liquor are produced.
  • the cooking liquor used in the sulfate process is white liquor containing NaOH and Na S.
  • the waste liquor is black liquor containing dissolved lignin, salts of organic acids, extractives, and a significant amount of inorganic compounds.
  • Black liquor is burned in a recovery boiler or other combustion device. As the organic and carbonous compounds in black liquor are combusted, the inorganic compounds in black liquor are transformed into chemicals that can be recirculated and reused in the digestion process. Black liquor is evaporated in a multistage evaporation plant to a higher dry solids content (60 - 90 %) for recovery. In order to recover chemicals and heat the concentrated black liquor is usually combusted in a recovery boiler. The pulp from the digestion, on the other hand, is washed and usually bleached as well for use as raw material for paper.
  • the digestion methods have recently developed enormously and different modifications especially of the sulfate method have been developed. It is typical of these modifications that during the digestion waste liquor is removed from the digester at two or more points of the digestion and correspondingly cooking liquor containing fresh chemical is added. This kind of adjustment of the chemical consistencies in the liquid surrounding the wood material during the digestion has an effect, for example, on the alkali and sulfide profile of the digestion and thus contributes to improving the properties of the pulp produced.
  • metals that may hamper the treatment of waste liquor after its removal from the digester may also be dissolved from the fibrous material in the cooking liquid during the digestion. Typical metals include calcium, aluminum, iron, magnesium, and copper.
  • Dissolved calcium is likely to form a complex with organic compounds in the digester, and as the waste liquor is evaporated the complex dissociates in the vicinity of a hot heat exchange surface. The released calcium ion then reacts with the carbonate in the liquor, and calcium carbonate forms scales on the heat exchange surface.
  • the complex between calcium and organic compounds dissociates during the digestion and calcium precipitates as carbonate into fibers in the digester and does not usually cause problems in the waste liquor evaporation plant.
  • Increased scaling in the waste liquor evaporation plant may occur if the waste liquor has been removed from the digester at a temperature below 150°C.
  • the first waste liquor flow may be removed at a temperature below 120°C.
  • the present invention relates to a method of preventing scale formation in a pulping process of chemical pulp, the method comprising at least the following steps: a) comminuted cellulosic fibrous material is treated with cooking liquor at a temperature below 120°C, b) a first waste liquor flow containing metals, e.g.
  • the key concept of the present invention is that by heat-treating those waste liquor flows removed from the digestion, the temperature of which has not risen to over 120°C during the process, scale formation during further treatment of waste liquor can be reduced, during which further treatment chemicals present in waste liquor are recovered and which further treatment typically includes evaporation before combustion in a recovery boiler.
  • the heat-treated first waste liquor flow is not recirculated to the digester.
  • the metal complexes typically calcium complexes, present in waste liquor dissociate.
  • the released calcium ions react with the carbonate in the liquor forming calcium carbonate crystals that remain in the liquor.
  • the heat treatment is typically carried out so that the liquor is not in contact with the heat exchange surface, but instead, in direct contact with a heat exchange medium such as steam.
  • the present invention is typically applied in connection with continuous digestion, where comminuted cellulosic fibrous material is treated at first with a first cooking liquor.
  • the purpose of this kind of treatment may be, for instance, to provide a high sulfide ion concentration at the beginning of the digestion.
  • the cooking liquor may be white liquor, or waste liquor separated in a later stage of the digestion, which waste liquor still contains significant amounts of digestion chemicals such as NaOH or Na?S.
  • the waste liquor is removed from the digestion at a temperature below 120°C, typically 95 - 115°C.
  • the amount of this liquor is typically 3 - 6 m 3 /adt, i.e. 25 - 75 % of the total waste liquor amount to be removed from the digestion.
  • cooking liquor normally white liquor
  • the temperature of the fiber suspension is elevated to 140 - 170°C to produce chemical pulp.
  • a second waste liquor flow the temperature of which is over 130°C, preferably 140 - 160°C, is removed from the digestion.
  • This waste liquor flow need not be heat-treated, because the metals in it are as compounds in the liquid, e.g. calcium carbonate crystals, that do not form scales during waste liquor evaporation in a multistage evaporation plant of waste liquor.
  • the first waste liquor flow is deactivated by heating it to over 120°C, preferably to 125 — 145°C, and the liquor is maintained at this temperature for at least 0.1 min, preferably 1 - 20 minutes, whereby calcium carbonate crystals are formed into the liquid.
  • the time is typically at least 0.1 - 5 minutes.
  • the heating is preferably practiced with the heat obtained from the second, hotter waste liquor flow.
  • the first and the second waste liquor flow can be mixed with each other. If, after being removed from the digestion, the second waste liquor flow is still used for pretreatment of fibrous material the waste liquor is flashed and the steam produced is brought into direct contact with the first waste liquor flow in order to heat this colder liquor to a desired heat treatment temperature.
  • the heat treatment may be intensified by introducing additional steam to the heat treatment vessel into direct contact with the waste liquor.
  • the second waste liquor flow may be heated with steam in a heat exchanger before this liquor flow is used for heating the first liquor flow.
  • the amount of the first waste liquor to be heat-treated may be reduced by pre-evaporating it before deactivation.
  • the important thing here is that the temperature during evaporation, and especially on the heat exchange surfaces, is so low that the organic complexes of calcium do not dissociate, because that could cause calcium scales on the heat exchange surfaces.
  • the temperature must be lower than the temperature of the waste liquor when being removed from the digestion.
  • the evaporation temperature is below 110°C, preferably below 90°C, even below 70°C.
  • the amount of the first waste liquor flow can be reduced by over 30 %, even by over 60 %.
  • the amount of energy needed in the heat treatment diminishes, because there is less liquid to be heated.
  • acid effluents are often produced which may also contain high amounts of metals, e.g. calcium, that form complexes with organic compounds. Due to closed water circulations bleaching effluents must also be treated further in the mill. It is often possible to treat bleaching effluents together with waste liquor, whereby, however, the metal compounds in the bleaching effluents may increase scale formation in the waste liquor evaporation plant.
  • metals e.g. calcium
  • bleaching effluents may be treated together with the first waste liquor flow in heat treatment.
  • the bleaching effluents may be pre- evaporated with waste liquor before the heat treatment.
  • special care must be taken to ensure that the temperature on the heat exchange surfaces is low. To prevent scaling it may be necessary to treat bleaching effluents at a lower temperature than the first waste liquor.
  • the temperature on the heat exchange surfaces is preferably below 90°C, even below 70°C, after adding bleaching effluents. For this reason it might be necessary to add the bleaching effluents after the waste liquor has been evaporated in one stage at a higher temperature.
  • the boiling point rise of the mixture of the first waste liquor and bleaching effluent is so small that in most cases it is possible to use a two-stage pre-evaporation plant.
  • the mixture of bleaching effluents and liquor is evaporated at a lower temperature than liquor.
  • bleaching effluents may be evaporated separately before feeding to waste liquor pre-evaporation plant.
  • the normal amount of bleaching effluent introduced from the bleach plant to the treatment of the first waste liquor is 1 - 8 m 3 /adt, preferably 1 - 5 m adt.
  • the temperature is below 100°C, typically 60 - 90°C.
  • the pH is normally 3 - 6.
  • the invention may be applied in particular in connection with continuous digesters but also with batch digestion having pre-impregnation or pretreatment of the fibrous material at a temperature below 120°C before the digestion.
  • the amount of waste liquor to be heat-treated is only about 50 % compared to systems in which the entire waste liquor flow is treated. If waste liquor is pre-evaporated the amount is only about 25 % of the total waste liquor flow.
  • bleaching effluents may be integrated in the system and thus no separate system is needed for the bleaching effluents.
  • bleaching effluents are simply added to the waste liquor treatment system. This addition enables, for example, the use of a two-stage evaporation plant, which improves the heat economy and reduces the consumption of fresh steam.
  • Figure 1 illustrates schematically a preferred embodiment of the invention
  • Figure 2 illustrates schematically another preferred embodiment of the invention
  • Figure 3 illustrates schematically a third preferred embodiment of the invention
  • Figure 4 illustrates schematically a fourth preferred embodiment of the invention, disclosing an evaporation plant configuration.
  • a suspension of comminuted fibrous material, e.g. wood chips, and white liquor is supplied from line 2 to the top of a continuous digester 1.
  • cooking chemicals absorb into the wood material at a temperature of 80 - 120°C, preferably 90 - 105°C.
  • alkali of the cooking liquor is consumed, and 15 - 20 % of the wood as well as a considerable part of the metals, especially of calcium, are dissolved.
  • a first waste liquor flow is separated from the fibrous material at screen 3 through line 4.
  • the treatment temperature is below 120°C, and the temperature of the waste liquor to be removed is typically 95 - 115°C.
  • this cooking liquor e.g. white liquor
  • the temperature of the fibrous material suspension is elevated to 140 - 170°C in order to produce chemical pulp.
  • a second waste liquor flow is separated from the pulp at screen 6 through line 7.
  • the first waste liquor flow 4 may contain, to a detrimental extent, calcium or other metal complexes that are deactivated with the method according to the invention. For this reason the first waste liquor flow is heated to a temperature of over 120°C preferably by means of heat from the second waste liquor flow by mixing the waste liquor flows into line 10. The liquor mixture is maintained at this temperature preferably in a separate retention tank 11 typically for 1 - 20 minutes in order to dissociate the calcium complex and to form calcium carbonate crystals. If necessary, steam can be brought from line 12 into the heat treatment vessel, which steam is then brought into direct contact with the liquor. Alternatively, the second waste liquor flow may be heated with steam in heat exchanger 9 before mixing. The first waste liquor flow cannot usually be heated in an indirect heat exchanger, because that would cause calcium carbonate scales on the heat exchange surfaces.
  • the heat-treated waste liquor in line 13 is supplied to further treatment through flashing 15 and line 16. Further treatment typically includes evaporation to a high dry solids content (60 - 90 %) for combustion. Turpentine may be separated from the steam obtained from flashing 15, which is one of the advantages of the invention.
  • the heat economy of the system may be improved by heating white liquor coming in line
  • White liquor is introduced into a desired location in the digester, for example through line
  • FIG 2 illustrates an embodiment in which the removed waste liquor flows are kept separate and only the first waste liquor flow is heat-treated.
  • the same reference numbers as in Figure 1 are used where applicable with the number "2" added to the front.
  • a suspension of chips is brought from line 22 to digester 21, and the suspension is treated at the top of the digester with waste liquor removed from the digester in a later step.
  • the liquor still contains significant amounts of cooking chemicals, because the waste liquor has been removed from the digestion in a step where the chemicals have not yet been consumed to a low concentration.
  • a first waste liquor having a temperature below 120°C is separated from the fibrous material to line 24.
  • the heat-treated liquor in line 213 is supplied through flashing 215 and then along line 216 to further treatment.
  • White liquor to be fed to the digester may be heated with the second waste liquor flow either prior to flashing 218 in heat exchanger 28 or after flashing in heat exchanger 221.
  • Figure 3 illustrates an embodiment in which also the first and second waste liquor flows are kept separate although the reason for keeping the flows separate is not the returning of the second liquor flow to the digester but, for example, the intensifying of the recovery of soap or turpentine.
  • the same reference numbers as in Figure 1 are used where applicable, with the number "3" added to the front.
  • the first waste liquor flow removed from digester 31 is heated in line 34 with steam obtained from the second waste liquor flow 37 in flashing 318.
  • the flashed second waste liquor flow in line 320 is flashed again in tank 322 and the waste liquor is supplied through line 323 to further treatment.
  • FIG 4 illustrates an embodiment in which the waste liquor to be heat-treated is pre- evaporated, and the treatment of bleaching effluents is integrated in this process.
  • Cellulosic fibrous material 42 is treated in digester 41 in the same way as described above.
  • the first waste liquor flow in line 44 has a temperature below 120°C and is heat- treated according to the invention. Before this, however, the liquor flow is pre-evaporated in evaporation plant 425, which causes a decrease in the amount of liquid to be fed to heat treatment as well as in the amount of energy needed for the heating.
  • the amount of energy needed for the pre-evaporation is also small, because the pre- evaporation is carried out at a temperature lower than the temperature at which the first waste liquor is removed, i.e. below 120°C, preferably below 110°C, most preferably below 90°C, even below 70°C. It is important to carry out the pre-evaporation at a temperature as low as possible to prevent calcium or other complexes in the waste liquor from dissociating and forming scales on the evaporation surfaces.
  • the amount of waste liquor typically being 3 - 6 m /adt, may be reduced in pre-evaporation by 30 %, preferably by over 60 %, which means considerable energy savings in view of the heat treatment.
  • the treatment of bleaching effluents may be integrated with the treatment of waste liquor.
  • acid bleaching effluents in particular may contain, to a detrimental extent, calcium or other heat sensitive complexes.
  • Bleaching effluents are added from line 424 to the first waste liquor flow, which has the favourable effect of increasing the pH of the effluents.
  • the precipitation of calcium carbonates or other such compounds in heat treatment requires a sufficiently high pH, for example 10 - 12 for calcium carbonate.
  • bleaching effluents are evaporated together with the first waste liquor, it must be ensured that the evaporation temperature is low enough. Bleaching effluents may require a lower temperature, because of higher tendency to form scales. For this reason it may be advisable to add bleaching effluent to the first waste liquor only after the waste liquor has been evaporated in one stage at a higher temperature than is advantageous for the evaporation of bleaching effluent.
  • the amount of bleaching effluent to be added to the first waste liquor flow is 1 - 8 m 3 /adt, preferably 1 - 5 m 3 /adt.
  • the temperature is below 100°C, typically 70°C.
  • Metal tube evaporators or lamella evaporators are preferably used. Particularly advantageous are falling film evaporators.
  • the pre-evaporated mixture of waste liquor and bleaching effluent is passed along line 426 to heat treatment 411. Since the evaporation temperature in the pre-evaporation is low, it is advantageous to preheat the pre-evaporated liquid to a temperature close to that of the first waste liquor removed from the digester, preferably to over 80°C, most preferably to over 100°C.
  • the preheating may be carried out in heat exchanger 427 with the liquor flow to be fed to the pre-evaporation plant.
  • the pre-evaporated and preheated liquor -bleaching effluent mixture is heat-treated in stage 41 1.
  • the second waste liquor flow 47 from the digester is flashed as described in connection with the other figures.
  • the flashed second waste liquor flow in line 420 and the heat- treated waste liquor-bleaching effluent mixture in line 426 are evaporated in a conventional multistage evaporation plant 427 of a pulp mill, the evaporation plant typically comprising 5 to 7 stages, and the waste liquor is evaporated to a dry solids content of 60 - 90 %.
  • the first stage of the multistage evaporation plant operates on fresh steam 428, which, if necessary, may also be used in the heat treatment 41 1.
  • Secondary steam 429 produced in the multistage evaporation plant may, if necessary, be used in the heat treatment 411 for direct steam heating. Secondary steam may also be used in pre- evaporation 425. Steam from flashing 418 of the second waste liquor may be used in the same way.
  • the evaporated liquor is supplied to combustion through line 430.

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  • Paper (AREA)
  • Removal Of Specific Substances (AREA)
  • Processing Of Solid Wastes (AREA)

Abstract

L'invention concerne un procédé de prévention de l'incrustation dans un procédé de fabrication de la pâte à papier chimique. Ledit procédé consiste au moins à : a) traiter une matière fibreuse cellulosique hachée à l'aide de lessive de cuisson, à une température inférieure à 120 °C, b) séparer de la matière un premier flux de lessive résiduaire contenant des métaux comme du calcium, de manière qu'un flux de lessive résiduaire soit produit, dont la température est inférieure à 120 °C, c) ajouter de la lessive de cuisson neuve à la matière fibreuse, d) digérer la matière fibreuse à une température de 140-170 °C de manière que de la pâte à papier chimique soit produite, e) séparer un deuxième flux de lessive résiduaire de la pâte à papier de manière qu'un flux de lessive résiduaire soit produit, dont la température est supérieure à 130 °C, f) chauffer le premier flux de lessive résiduaire de l'étape b) de sorte que sa température dépasse 120 °C, g) maintenir le flux de lessive résiduaire de l'étape f) à une température supérieure à 120 °C pendant au moins 0,1 min, de préférence 1-20 min, de sorte que la précipitation des métaux, notamment le calcium, présents dans ladite lessive résiduaire, soit induite, h) soumettre le flux de lessive résiduaire traité thermiquement à un autre traitement, et I) lessiver la pâte de l'étape e).
PCT/FI1999/000689 1998-08-21 1999-08-20 Procede de prevention de l'incrustation WO2000011263A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI981803 1998-08-21
FI981803A FI981803A7 (fi) 1998-08-21 1998-08-21 Menetelmä saostumien muodostumisen estämiseksi

Publications (1)

Publication Number Publication Date
WO2000011263A1 true WO2000011263A1 (fr) 2000-03-02

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PCT/FI1999/000689 WO2000011263A1 (fr) 1998-08-21 1999-08-20 Procede de prevention de l'incrustation

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FI (1) FI981803A7 (fr)
WO (1) WO2000011263A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001025531A1 (fr) * 1999-10-04 2001-04-12 Metso Chemical Pulping Oy Procede destine a prevenir l'entartrage des surfaces d'echange thermique
JP2002155484A (ja) * 2000-11-03 2002-05-31 Kvaerner Pulping Ab パルプの連続蒸煮プロセス
WO2006012286A1 (fr) * 2004-06-26 2006-02-02 International Paper Company Procede pour diminuer l'entartrage des systemes lessiveurs
WO2013036190A1 (fr) 2011-09-05 2013-03-14 Stora Enso Oyj Procédé pour le traitement de liqueur noire de bois de feuillus et liqueur noire de bois de feuillus traitée selon le procédé
US8986504B1 (en) 2013-10-25 2015-03-24 International Paper Company Digester apparatus

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4755258A (en) * 1985-06-06 1988-07-05 Ahlstromforetagen Svenska Ab Method and apparatus for deactivating spent liquor
EP0313730A1 (fr) * 1987-10-26 1989-05-03 Kamyr, Inc. Appareils et procédés pour réduire la formation de dépôts dans les processus de mise en pâte
US5674359A (en) * 1995-02-08 1997-10-07 Ahlstrom Machinery Inc. Continuous cooking of cellulosic fibrous material with cold alkali impregnation
WO1999002771A1 (fr) * 1997-07-11 1999-01-21 Sunds Defibrator Pori Oy Procede servant a traiter de la liqueur residuaire generee par la fabrication de pate a papier kraft

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4755258A (en) * 1985-06-06 1988-07-05 Ahlstromforetagen Svenska Ab Method and apparatus for deactivating spent liquor
EP0313730A1 (fr) * 1987-10-26 1989-05-03 Kamyr, Inc. Appareils et procédés pour réduire la formation de dépôts dans les processus de mise en pâte
US5674359A (en) * 1995-02-08 1997-10-07 Ahlstrom Machinery Inc. Continuous cooking of cellulosic fibrous material with cold alkali impregnation
WO1999002771A1 (fr) * 1997-07-11 1999-01-21 Sunds Defibrator Pori Oy Procede servant a traiter de la liqueur residuaire generee par la fabrication de pate a papier kraft

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
THOMAS M. GRACE: "Evaporator Scaling. Research on the Reduction or Elimination of Calcium Scales", SOUTHERN PULP AND PAPER MANUFACTURER, vol. 40, no. 8, August 1977 (1977-08-01), pages 16 - 23 *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001025531A1 (fr) * 1999-10-04 2001-04-12 Metso Chemical Pulping Oy Procede destine a prevenir l'entartrage des surfaces d'echange thermique
US6939439B1 (en) 1999-10-04 2005-09-06 Metso Chemical Pulping Oy Batch process for producing chemical pulp by removing and reintroducing calcium-containing spent liquor in the digester
JP2002155484A (ja) * 2000-11-03 2002-05-31 Kvaerner Pulping Ab パルプの連続蒸煮プロセス
WO2006012286A1 (fr) * 2004-06-26 2006-02-02 International Paper Company Procede pour diminuer l'entartrage des systemes lessiveurs
US7241363B2 (en) 2004-06-26 2007-07-10 International Paper Company Methods to decrease scaling in digester systems
RU2386737C2 (ru) * 2004-06-26 2010-04-20 Интернэшнл Пэйпа Кампани Способ уменьшения накипи в системах варочных котлов
US7918967B2 (en) 2004-06-26 2011-04-05 International Paper Company Apparatus for decreasing scaling in digester systems
WO2013036190A1 (fr) 2011-09-05 2013-03-14 Stora Enso Oyj Procédé pour le traitement de liqueur noire de bois de feuillus et liqueur noire de bois de feuillus traitée selon le procédé
EP2753750A4 (fr) * 2011-09-05 2015-04-22 Stora Enso Oyj Procédé pour le traitement de liqueur noire de bois de feuillus et liqueur noire de bois de feuillus traitée selon le procédé
US8986504B1 (en) 2013-10-25 2015-03-24 International Paper Company Digester apparatus

Also Published As

Publication number Publication date
FI981803L (fi) 2000-02-22
FI981803A7 (fi) 2000-02-22
FI981803A0 (fi) 1998-08-21

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