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TMP long fibre fractionation with pressure screens : Contoured surface baskets are better than smooth surface baskets

Pulp & paper Canada, 1997-12, Vol.98 (12), p.179-182

1998 INIST-CNRS ;Copyright Southam Business Communications, Inc. Dec 1997 ;ISSN: 0316-4004 ;EISSN: 1923-3515 ;CODEN: PPCADD

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  • Title:
    TMP long fibre fractionation with pressure screens : Contoured surface baskets are better than smooth surface baskets
  • Author: WAKELIN, R. F ; CORSON, S. R
  • Subjects: Applied sciences ; Equipment & supplies ; Exact sciences and technology ; Paper, paperboard, non wovens ; Polymer industry, paints, wood ; Pulp & paper industry ; Pulp & paper mills ; Pulp manufacturing ; R&D ; Research & development ; Wood. Paper. Non wovens
  • Is Part Of: Pulp & paper Canada, 1997-12, Vol.98 (12), p.179-182
  • Description: The fractionation is greater for smaller aperture dimensions for both the smooth and contoured surfaces, Fig. 1. The smooth surface baskets allow considerably higher efficiencies than either of the contoured surface baskets, and the smooth surface 1.0-mm hole basket can achieve almost complete removal of the R14 fraction. The gentler mixing action of the Bump rotor yields greater efficiencies compared with the LR rotor, but the increase in reject thickening appears to outweigh this gain. The sharp decrease in reject thickening at low rotor speeds for the smooth surface baskets is associated with an equally sharp reduction in fractionation efficiency, indicating that more of the long fibre is passing through the apertures. The long fibre fractionation efficiency achieved with smooth surface screen baskets depends on the relationship between the fibre length of the fraction of interest and the aperture dimension, Fig. 2. The fractionation efficiencies for the Bauer McNett R14 and 14/30 long fibre fractions are shown for smooth surface screen baskets with hole diameters ranging from 0.8 to 1.4 mm. The fibre orientation mechanism also suggests a dependence of the fractionation efficiency on the ratio of fibre length to aperture dimension. Given that the average fibre lengths of the R14 and 14/30 fractions are around 3-and 1.9-mm respectively(f.10), the (L/W > 2) guideline proposed by [Kumar](f.6) would require aperture dimensions of less than 1.5- and 1.0-mm, respectively, for their efficient removal, (Q > 0.8). This is in reasonable agreement with the results presented in Fig. 2. The capacity of the fine slot basket is less than three-quarters that of the 1.40-mm smooth surface holed basket, at a rotor speed that gives equivalent reject thickening and fractionation efficiency. The Vacuum Foil rotor reduces the thickening and fractionation efficiency relative to the results obtained with the Bump rotor and has a steeper response to rotor speed changes. The toplog pulp has higher reject thickening and fractionation efficiency than the thinnings when screened with the 1.40-mm smooth hole basket (Figs 3 and 4) or the 0.30-mm contoured surface slot basket, Fig. 3 versus(f.1), and Fig. 4 versus Fig. 1. This may be attributable to the influence of the longer and coarser fibres of the toplog relative to the thinnings wood. The critical rotor speed for the failure of the smooth surface screen also appears to be lower with the thinnings, but further data is required to confirm this.
  • Publisher: Don Mills, ON: Southam
  • Language: English
  • Identifier: ISSN: 0316-4004
    EISSN: 1923-3515
    CODEN: PPCADD
  • Source: ProQuest Central
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