CHANGES ON THE OXYGEN STAGE IN A SOFTWOOD FIBER LINE

Oxygen delignification is the use of oxygen in alkaline environment aiming the removal of a substantial fraction of residual lignin from the unbleached cellulosic pulp. This research evaluated the influence of temperature, alkali charge, O2 charge and work pressure at oxygen stage in a softwood fiber line. This work was developed in a softwood fiber line. The pulping process is SuperBacthTM, a modified kraft process, and the current bleaching sequence of this fiber line is O-EOP-D1-PO1-PO2-D2. The parameters relevant to the cellulosic pulp were measured at each bleaching stage. The most influential parameter at oxygen stage is the temperature, followed by alkaline charge. In general it was possible to decrease the consumption of chlorine dioxide using more severe conditions in O stage. The best change was the number three, because it has a higher kappa reduction, a higher selectivity and lower viscosity loss than the normal condition. For the refining results, the change number three had also satisfactory results. It showed the same tensile index and fiber length when compared with the normal bleaching condition, and also a quite similar coarseness.