Installing Ozone Bleaching and Hot Acid Treatment at NPI Mills

Nippon Paper Industries, Co., Ltd. declared conversion of all the bleaching process to ECF, and most of the production had converted by now. To reduce ECF bleaching cost, we found that depending on electricity supply condition of the mill, utilization of ozone bleaching could be very effective. In addition, hot acid treatment of unbleached pulp also seemed to be effective for hardwood. In this study, several conditions for each technology were examined with the pulps from our own mills to reduce bleaching cost and to keep fiber quality acceptable level. In hot acid treatment study, with mild conditions (temperature lower than $90^{\circ}C$), sufficient reduction in Kappa number and hexenuronic acids content of the pulp were observed, while pulp viscosity was maintained. Moreover, to maintain strength of bleached pulp that subjected both to ozone bleaching and hot acid treatment, recommended Kappa number after ozone bleaching was more than 3. Based on these findings, two of our mills had installed medium-consistency ozone bleaching facilities and three mills installed hot acid treatment. Especially in Yatsushiro mill, both were installed in one bleaching line (A-ZD-E/P-D sequence), and running successfully.