Oxygen bleaching sequence, efficient washing system and reinforced effluent treatment facilities that had been introduced in Hachinohe mill of Mitsubishi Paper Mill since 1988, was allowed to reduce adsorbed organic halogen (AOX) with greatefficiency. However the global environmental demand intensely trends toward more and more reduction of emission or pollution. In view of the situation, the introduction of the elemental chlorine free (ECF) bleaching sequence to Hachinohe mill has been decided in 1999.
In October 2000, No. 3 BKP-line, the product line of LBKP, was adapted for ECF bleaching sequence with the minimum conversion of existent bleaching facilities except continuous cooker, washing facilities oxygen bleaching stage and so on. D0 (E/O) PD, sequence, in which the existent bleaching towers could be used, was selected for the ECF bleaching sequence on No. 3 BKP-line.
It was found that the brightness of oxygen-bleached pulp instead of the kappa number of Oxygen-bleached pulp dominated the bleaching efficiency on ECF bleaching sequence in contrast with the conventional chlorine bleaching sequence. In the operation of ECF bleaching sequence, the prevention of scale and the reduction of bleaching chemicals have been carried out.
In this report, we describe the operational experience of ECF bleaching in this last year and discuss the main issues in ECF bleaching such as the influence of hexeneuronic acid in unbleachedpulp.
