STOICHIOMETRIC MODEL OF CHLORINE DIOXIDE DELIGNIFICATION OF HARDWOOD KRAFT PULPS WITH OXIDANT-REINFORCED EXTRACTION EFFECTS

摘要

A generalized, steady-state model for hardwoods has been proposed for predicting bleaching delignification and/or chlorine dioxide consumption for sequences that employ oxidant-reinforced extraction. Published literature data using various hardwood species and mixtures were analyzed to develop the model. The kappa number data from these studies were normalized to their respective pre-Do kappa number, and the normalized kappa numbers were plotted against the bleach demand. This mathematical transformation allowed for various brownstocks and oxygen-delignified pulps with different kappa numbers to be model as a single curve based on an empirical relationship with fitted equation parameters. One of the two equation parameters could be expressed as simple functions of oxidant-reinforced extraction conditions (i.e., peroxide dosage). The model forecasts chlorine dioxide usage reasonably well (±0.20% ClO2 on pulp) for conventional chlorine dioxide delignification with extraction. Unsuccessful attempts were made to incorporate modified bleaching delignification processes that eliminate hexenuronic acids into the model; no relationship could be developed due to insufficient data. This straightforward stoichiometric model contains relatively few fitted parameters to be determined. The model could be used with other steady-state brightening stage models to predict bleach usage. Application: The hardwood stoichiometric model predicts chlorine dioxide consumption during bleaching delignification for mills utilizing ECF bleaching sequence that utilize oxidant-reinforced extraction stages. Other applications of the model include bleach plant optimizations, computer simulations, and/or process control strategies.