ECF Bleaching for Meeting U.S. EPA Cluster Water Rules with Conventional Cooked Kraft Softwoods

摘要

As environmental demands grow mills have a number of options for meeting the new regulations. This study examines options available for conventionally cooked kraft softwood pulps of about 30 kappa. The focus of this study is on ECF bleaching sequences based on oxygen, chlorine dioxide and peroxide in D(Eop/Pht)DD and OD(Eop/Pht)DD sequences to 86-88%ISO brightness. The objective of the study is to use base data and correlate issues on system flexibility for brownstock carryover, various bleaching stage intensities and the impact from filtrate recirculation. Outcomes that are tracked include bleach plant outfall, as color, COD and AOX, and the impact on pulp characteristics, including brightness development and physical strength. System impacts that are explored, in relation to U.S. EPA Water Cluster Rule Regulations, include:rn1. Oxygen delignification degree (0→ 47%)rn2.D_0 kappa factor (0.08→ 0.24)rn3.Peroxide use in Extraction (0.4→1.2%)rn4. Brownstock carryover (5→15 kg COD/ mt)