New and Improved Models for All Stages in Full ECF Bleaching Sequences of Softwoods and Hardwoods

This study presents new and improved semi-empirical mathematical models for all the chlorine dioxide stages and extraction stages (including oxygen and/or peroxide reinforced) incorporated in a full Elemental Chlorine Free (ECF) bleaching sequence simulator developed in EFPG. The simulator predicts variations of Kappa number, pH, brightness, bleaching chemical consumption and COD at each step of multistage ECF bleaching sequences. The first purpose of this work was to improve kinetic and stoichiometric equations, involved in the chlorine dioxide stages (Do, D1, D2), for their predictability for different kinds of softwood and hardwood pulps. The second purpose was to model the extraction stages with or without oxygen and/or hydrogen peroxide reinforcement (E, EO, EOP, EP). The results predicted fit very closely to a wide range of laboratory and mill bleaching data and the predictability was extended to a greater variety of pulps (softwoods and hardwood pulps, kraft or other alkaline pulps).