EP0296198B1 - Method for washing of alcaline pulp - Google Patents

Method for washing of alcaline pulp Download PDF

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Publication number
EP0296198B1
EP0296198B1 EP19880900488 EP88900488A EP0296198B1 EP 0296198 B1 EP0296198 B1 EP 0296198B1 EP 19880900488 EP19880900488 EP 19880900488 EP 88900488 A EP88900488 A EP 88900488A EP 0296198 B1 EP0296198 B1 EP 0296198B1
Authority
EP
European Patent Office
Prior art keywords
washing
pulp
carbon dioxide
stage
filtrate
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
Application number
EP19880900488
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German (de)
English (en)
French (fr)
Other versions
EP0296198A1 (en
Inventor
Monica BOKSTRÖM
Raimo Rasimus
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Linde Sverige AB
Original Assignee
AGA 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
Priority claimed from SE8605510A external-priority patent/SE8605510L/
Application filed by AGA AB filed Critical AGA AB
Priority to AT88900488T priority Critical patent/ATE67536T1/de
Publication of EP0296198A1 publication Critical patent/EP0296198A1/en
Application granted granted Critical
Publication of EP0296198B1 publication Critical patent/EP0296198B1/en
Expired legal-status Critical Current

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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
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents

Definitions

  • the present invention relates to a method in the washing of alkaline, cellulosic pulp, the washing being effected in one or more consecutive stages.
  • US-A-4042452 relates to a system wherein the total washing efficiency is increased by lowering the pH value in one or several liquid cycles of a washing system. In addition to increased efficiency, some advantages are thereby gained: If the pH of spent liquor is lowered, its color becomes considerably lighter. Also, foaming is reduced when the pH value is lowered. An acid wash considerably increases the brightness of the fibers, especially if an oxidizing acid is selected.
  • the oxidizing acid also oxidized sulfides, other reduced sulfur compounds and possibly hydrogen sulfide or mercaptan present into sulfites, sulfates, thiosulfates or elemental sulfur.
  • One object of the present invention is to reduce washing losses in the washing of alkaline pulp.
  • a further object of the present invention is to emasculate alkaline, cellulosic pulp of sodium ions.
  • a third object of the present invention is to increase the washing-out, from alkaline, cellulosic pulp, of substances which contribute to chemical oxygen demand (COD).
  • COD chemical oxygen demand
  • the pH is lowered to approximately 9.
  • the pH is lowered by carbon dioxide in one or more washing stages, as a result of which there will be attained an improved washing-out from the pulp of substances which contribute to chemical oxygen demand (COD).
  • COD chemical oxygen demand
  • the preferred agent for realising an improved washing of the pulp is carbon dioxide which is added to washing water used in the washing of the pulp and/or to the pulp suspension, prior to the washing stage. Possibly, carbon dioxide may also be added to the washing stage proper.
  • Carbon dioxide is the particularly preferred agent for attaining improved washing results. Carbon dioxide contains no environmentally hazardous substances such as chlorine or sulphur.
  • sulphuric acid which, granted, contains sulphur, since the pulp which is washed according to the present invention has been treated, prior to the washing ⁇ with sulphate-containing treatment liquid.
  • sulphuric acid is preferably added together with carbon dioxide in order to achieve a more manifest reduction of pH. This said, the pH should not be reduced overly much, since undersirable reactions with residual lignin may then occur.
  • the pulp which can be washed with an addition of carbon dioxide or other pH reducing agent is sulphate pulp of softwood and deciduous or hardwood, and also chemi-mechanical pulp, CTMP and CMP.
  • the pH reducing agent is added in one or more stages, the agent not being added at least in the first washing stage.
  • the pH is reduced in the last stage of, for example three or four washing stages, to approximately 5.
  • use may also be made, in addition to carbon dioxide, of a mineral acid, especially sulphuric acid.
  • reference numeral 51 in fig. 1 designates a source for carbon dioxide which, by the intermediary of a conduit 57, is in communication with a rotameter 52, a manometer 53 and a vessel 54.
  • the bottom 58 of the vessel 54 is a sintered body which finely divides the gas entering from the source 51.
  • the contents of the vessel 54 are agitated by means of an agitator 55 driven by a motor 56.
  • the COD washing-out procedure is more complicated. Total amount of washed-out COD will be higher in an addition of CO2 in the 2nd washing stage. However, the effect is delayed and the improved washing effect does not become apparent until the 3rd washing stage.
  • CaCO3 is more sparingly soluble than (RCOO)2 Ca
  • Na (tot) relates to the quotient of total washed-out Na
  • pH(2) refers to pH after the second washing stage.
  • Calcium carbonate is deposited temporarily, calcium being "inactivated".
  • Calcium soaps are insoluble in character and do not form lamellar phases to the same extent as sodium soaps. The surface activity in the system increases, which gives an improved washing-out of organic substance.
  • a trial has been made to wash birch kraft pulp counter-currently on a laboratory scale.
  • the purpose of this trial is to get closer to full scale conditions by using a counter-current method and to make this washing on birch kraft pulp having a higher extract content than pine kraft pulp.
  • the washing steps are schematically shown in figure 2.
  • a batch of pulp suspension is supplied to the first washing, step 61, and washed by using the filtrate from the second step 62.
  • the pulp washed in the first step is thereafter supplied to the second step 62 and washed with filtrate from the third step 63.
  • the pulp washed in the second step thereafter is supplied to the third step in which said pulp is washed with filtrate from the fourth step 64.
  • the pulp is washed with filtrate from the fifth step 65.
  • the pulp is washed with deionized water.
  • step 62 then was used as washing liquid in step 61 for batch No. 3.
  • the filtrate, 700 ml, from step 1 was discarded.
  • batch No. 1 was washed in step 64 with 700 ml of deionized water and finally in step 65 with 700 ml deionized water.
  • the filtrate, 700 ml from batch No. 1 in step 65 then was used as washing liquid for the next batch. Thereafter deionized water was added only to step 65 and the filtrate from that step was used for washing the next batch in step 64, etc.
  • the filtrate from step 61 for the 12 first batches was discarded. Then the last four filtrates from step 61 were taken care of, brought together to a comparative sample and analyzed.
  • step 65 carbon dioxide was added to step 65.
  • the carbon dioxide was added during the washing, which took some minutes and took place during stirring of the pulp suspension deionized water.
  • the steady state condition was built up in the same manner as was done in the reference series without carbon dioxide.
  • the last four filtrates from step 61 out of the 16 filtrates obtained were brought together and analyzed.
  • filtrate 61 designates filtrate from step 61
  • filtrate 62 designates filtrate from step 62, etc.
  • Washed pulp i.e. pulp from batches 12-16 were brought together to one sample, and filtrate 61 was analyzed further.
  • Filtrate 61 designates the last four filtrates in each series containing 16 batches taken from step 61 brought together to an average sample. The results from the analysis of the filtrate are shown in table 3.
  • a modified plant for washing of pulp in sulphate cooking is illustrated in fig. 3
  • the pulp comes from a digester (not shown) through a conduit 1 to a blow tank 3.
  • the conduit 2 leads to a blow condensor.
  • the pulp in the blow tank 3 is diluted with weak (thin) liquor via a conduit 4 from a weak liquor cistern 19.
  • An agitator in the blow tank 3 is designated 5.
  • the pulp from the blow tank 3 is passed through a conduit 29 to a knotter screen 6.
  • the pulp passes thence to the first washing filter 15 and subsequently to the three following washing filters 16, 17 and 18.
  • the filtrate from the first filter 15 is collected in the weak liquor cistern 19 and the filtrate from the other three filters in the washing liquor cisterns 20, 21 and 22, respectively.
  • the washed pulp departs from the fourth filter 18 at reference numeral 13.
  • the filter cake is comminuted by shredders 8. Filtrate from one filter is used as washing liquid in the preceding filter and dilution liquid in the same filter. Normally, pure water is added to the last filter 18 as washing liquid, entering through a conduit 12.
  • carbon dioxide is introduced into the conduits 31 and/or 32 via conduits 23 and 24, respectively.
  • the carbon dioxide dissolves at once in the washing liquid and is led to the filters 17 and 18, respectively through the conduits 31 and 32 and the conduits 10 and 11.
  • the filtrate from the filter 16 passes through a conduit 26 to the cistern 20.
  • a pH sensor device is disposed either in the cistern 20 or in the conduit 26, the sensor controlling, by the intermediary of the control and regulation equipment, the supply of carbon dioxide to the conduit 31.
  • Water is added to the last washing filter 18, this water being admixed with carbon dioxide and/or sulphur dioxide.
  • a pH sensor device may also be disposed in the conduit 28.
  • the cellulosic material is pre-treated with alkaline treatment liquid and is disintegrated in one or more refiners, normally disc refiners.
  • the pulp suspension passes thence to a screen room.
  • the accept therefrom then passes to a washing plant, for example of the type illustrated in fig. 3.

Landscapes

  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
EP19880900488 1986-12-22 1987-12-21 Method for washing of alcaline pulp Expired EP0296198B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT88900488T ATE67536T1 (de) 1986-12-22 1987-12-21 Verfahren zum waschen einer alkalischen pulpe.

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
SE8605510 1986-12-22
SE8605510A SE8605510L (sv) 1986-12-22 1986-12-22 Sett vid tvettning av massa
WOPCT/SE87/00198 1987-04-16
PCT/SE1987/000198 WO1988004705A1 (en) 1986-12-22 1987-04-16 Method for washing of alcaline pulp

Publications (2)

Publication Number Publication Date
EP0296198A1 EP0296198A1 (en) 1988-12-28
EP0296198B1 true EP0296198B1 (en) 1991-09-18

Family

ID=26659637

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19880900488 Expired EP0296198B1 (en) 1986-12-22 1987-12-21 Method for washing of alcaline pulp

Country Status (3)

Country Link
EP (1) EP0296198B1 (enrdf_load_stackoverflow)
DE (1) DE3773204D1 (enrdf_load_stackoverflow)
WO (1) WO1988004706A1 (enrdf_load_stackoverflow)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000073576A1 (en) * 1999-06-01 2000-12-07 Aga Aktiebolag Bleaching of lignin and process for producing paper
US7056419B2 (en) 2002-09-30 2006-06-06 American Air Liquide, Inc. Methods for modifying electrical properties of papermaking compositions using carbon dioxide

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5401362A (en) * 1993-03-24 1995-03-28 Kamyr, Inc. Control of metals and dissolved organics in the bleach plant
US5509999A (en) * 1993-03-24 1996-04-23 Kamyr, Inc. Treatment of bleach plant effluents
SE502172C2 (sv) * 1993-12-15 1995-09-04 Mo Och Domsjoe Ab Förfarande för framställning av blekt cellulosamassa med en klorfri bleksekvens i närvaro av karbonat
SE502706E (sv) 1994-04-05 1999-09-27 Mo Och Domsjoe Ab Framställnng av blekt cellulosamassa genom blekning med klordioxid och behandling av komplexbildare i samma steg
SE516030C2 (sv) * 1994-11-14 2001-11-12 Aga Ab Regenerering av en gasblandning från ett ozonbleksteg
FI103520B1 (fi) * 1998-03-03 1999-07-15 Aga Ab Parannetut paperinvalmistusmenetelmät
FI110533B (fi) * 2000-05-04 2003-02-14 Aga Ab Menetelmä mikrobikasvun torjumiseksi
FI20070126A0 (fi) * 2006-09-08 2007-02-13 Linde Ag Menetelmä hartsin poistamiseksi massasta ja hiilidioksidin tai (bi)karbonaatin käyttö tähän tarkoitukseen
FI20075503A7 (fi) * 2007-07-03 2008-06-19 Linde Ag Menetelmä paperin valmistamiseksi ja happo/emäskäsittelyn käyttö paperin valmistuksessa

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FI52876C (fi) * 1974-09-03 1978-10-17 Ahlstroem Oy Foerfarande foer tvaettning av en cellulosamassa fraon alkalikok

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000073576A1 (en) * 1999-06-01 2000-12-07 Aga Aktiebolag Bleaching of lignin and process for producing paper
US7056419B2 (en) 2002-09-30 2006-06-06 American Air Liquide, Inc. Methods for modifying electrical properties of papermaking compositions using carbon dioxide

Also Published As

Publication number Publication date
DE3773204D1 (enrdf_load_stackoverflow) 1991-10-24
EP0296198A1 (en) 1988-12-28
WO1988004706A1 (en) 1988-06-30

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