High Consistency Ozone Bleaching Plants

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Other Title
  • 高濃度オゾン漂白の導入事例
  • オゾン漂白基礎講座(4)高濃度オゾン漂白の導入事例
  • オゾン ヒョウハク キソ コウザ(4)コウノウド オゾン ヒョウハク ノ ドウニュウ ジレイ

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Abstract

<p>The first commercial high consistency （HC） ozone bleaching started in 1992 at the Union Camp mill in Franklin （Virginia, USA）. According to the C-FreeⓇ process implemented there, the pulp was adjusted by pH, pressed to high consistency （40%）, fluffed and transferred to the ozone paddle reactor operating at at mospheric pressure. The C-FreeⓇ was provided by Sunds Defibrator until the late 1990’s in the USA, Swe den, South Africa and Germany. Modern HC ozone bleaching uses the ZeTracTM technology provided by Val met which is a much-simplified version of the C-Free Ⓡ. The experience gained for the first industrial installations has shown that ozone requires very short contacting time with the pulp for around one minute and that a 5-10 minutes extraction stage after the Z-stage without intermediate washing is in most cases suf ficient. Experience has shown that a 5-10 minutes e-stage at 11-12 percent pulp consistency, following the ozone treatment at high consistency produces results similar to those of a 60-90 minutes conventional ex traction stage. The pulp at 38-42 percent consistency is diluted directly with alkali, so the alkali reaches the heart of the fibers without the need of diffusion and quickly solubilizes the oxidized material. Then the press following the e-stage removes solubilized material from the fibers when pressing the pulp. These two aspects―the quick access to the fibers thanks to their high consistency, and the quick removal of the alkali with the press―eliminate the need for long diffusion times in an extraction tower （in the case of new bleach plants）. These observations permitted to reduce the size of reactors and to lower the investment costs. The plug screw feeder, the refiner fluffer and the washing stage prior to the extraction stage could all be eliminated. These drastic simplifications led to a significant reduction of the capital expenditure, energy requirement, maintenance costs as well as effluent volume.</p>

Journal

  • JAPAN TAPPI JOURNAL

    JAPAN TAPPI JOURNAL 71 (3), 305-311, 2017

    JAPAN TECHNICAL ASSOCIATION OF THE PULP AND PAPER INDUSTRY

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