BALANCING CHLORINE DIOXIDE AND PEROXIDE IN NORTH AMERICAN ECF BLEACHING SEQUENCES FOR SOFTWOOD KRAFT PULPS, 2008 Engineering, Pulping and Environmental Conference

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This investigation examines how oxidative alkaline extraction can be augmented through process condition changes, and how this augmentation can be leveraged to optimize chlorine dioxide usage and bleaching costs with elemental chlorine-free (ECF) sequences. The effects peroxide reinforcement and elevated extraction temperatures (>70°C) are not additive when both are used to lower post-extraction kappa number. This likely reflects competing physical and chemical mechanisms involved, and which modes are dominant at 70 to 80°C versus 90°C The economic advantages of peroxide reinforcement in 70°C (EOP) or 90°C (EO) are predisposed by the brightness targets, short or long bleach sequences and mill energy costs. It is observed that approximately 55 to 65% of the total chlorine dioxide used in an ECF sequence should be applied in the D₀-stage.