Current Bleaching Sequences in Nordic Kraft Pulp Mills, 1998 Pulping Conference Proceedings

Current performance data were collected for entire bleaching sequences in mills producing kraft pulp in the Nordic countries. The data were collected during the fall of 1997 by direct contact with the mills. Analyses of the data included the type of cooking, incoming kappa number of pulp before and after oxygen delignification, the bleaching sequence, process parameters, and to some extent chemical charges. Clear trends were found in the results. Oxygen delignification (O) was very predominant. The extraction stage (E) was often reinforced with both oxygen and peroxide early in the sequence, while peroxide only was used in the second extraction stage. Oxygen-reinforced peroxide stages (PO) were commonly used in TCF sequences and also in some ECF sequences. Ozone was commonly used in TCF bleaching, and also in ECF bleaching in mills producing both ECF and TCF pulp.

Five types of modern, future bleaching sequences, 3 ECF and 2 TCF sequences, were set up for laboratory trials based on the data collected from the mills. The purpose of the laboratory trials was to investigate the potential for alternative bleaching sequences. Bleaching tests were performed according to these sequences in which hardwood and softwood kraft pulps from both continuous and batch processes were used. The consumption of bleaching chemicals and optical properties of the pulps were determined throughout the sequence. The bleached pulps were PFI-beaten to determine strength properties.