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Scaling and bleaching chemicals consumption: A mill case

Pulp & paper Canada, 2004-03, Vol.105 (3), p.47-50

2004 INIST-CNRS ;Copyright Southam Business Communications, Inc. Mar 2004 ;ISSN: 0316-4004 ;EISSN: 1923-3515 ;CODEN: PPCADD

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  • Title:
    Scaling and bleaching chemicals consumption: A mill case
  • Author: Barata, P.A ; Marques, I.S
  • Subjects: Applied sciences ; Bleaching ; bleaching agents ; Brightness ; Exact sciences and technology ; Paper chemicals ; Paper, paperboard, non wovens ; Polymer industry, paints, wood ; Pulp & paper mills ; pulp and paper mills ; Pulp manufacturing ; Recovery of chemicals ; wood pulp ; Wood. Paper. Non wovens
  • Is Part Of: Pulp & paper Canada, 2004-03, Vol.105 (3), p.47-50
  • Description: Original Filtrate Circuit: The original bleach plant filtrate circuit were counter-current acidic/alkaline separate lines D2-D1-D0 and E2p-Eop, Fig. 1. Mill A had operational problems in bleach plant washing efficiency due to severe scaling of calcium carbonate in the Eop stage wash diffuser, and scaling of calcium oxalate in the D0 stage wash diffuser. The extraction flow in the D0 wash diffuser was reduced by 50% after around nine months of operation, but the severe problem was in the Eop stage, where the extraction flow was reduced by 75% in a very short period, that is, less than one month. This resulted in lack of pulp washing, which lead to a consumption increase of bleaching chemicals (namely, chlorine dioxide and sodium hydroxide), loss of pulp consistency and difficulties in reaching the desired brightness target. Although the pulp entering the bleach plant in Mill A has the same sodium as Mill B and lower COD, after the D0 and Eop stages the sodium and COD levels showed a large increase. The lack of washing in the initial stages D0-Eop has a detrimental effect on chemicals consumption in the last D1-E2p-D2 stages. When comparing the Mill B and Mill A bleach plants, the chlorine dioxide in D1+D2 stages of the reference bleach lines of Mill B used 85-90% for delignification and 10-15% was consumed by COD, but in Mill A 60% was used for delignification and 40% for COD consumption. New Filtrate Circuit: In order to solve the lack of washing in the initial stages of the bleach plant due to scaling, it was decided to change the bleach plant filtrate circuit from the existing counter-current acidic/alkaline separate lines to a unique counter-current line. However, due to the limitation regarding the materials of construction of the screen unit and scraper of the E2p stage wash diffuser (where acidic filtrate from D2 was not allowed), the final filtrate counter-current circuit was limited to E2p-D1-Eop stages. Thus the D2 filtrate was used in D0 stage, Fig. 5. With this modification it was expected to solve the calcium carbonate scaling in Eop stage, and a chemical chelant was added in D0 to inhibit the barium sulphate scaling. At the same time, the pulp acidification before D1 stage was no longer needed.
  • Publisher: Don Mills, ON: Southam
  • Language: English
  • Identifier: ISSN: 0316-4004
    EISSN: 1923-3515
    CODEN: PPCADD
  • Source: AUTh Library subscriptions: ProQuest Central
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