Medium Consistency Oxygen Delignification Design Utilizing a Two Phase Concept - Part 1, 1995 Pulping Conference Proceedings

William Miller

Ingersoll-Rand/Pulp Machinery Division

Heokbum Kwon

Annukka Liukkonen

Joseph Genco

University of Maine

Oxygen delignification is the cornerstone in many of the present day bleaching systems. Its role will only increase in North America as a means of meeting impending environmental requirements. It has become increasingly important that the understanding and application of this process continue to improve. This study will show how a two phase, medium consistency system can be designed for optimal control and results. An understanding of the reaction pathways will be the basis for the design concept. For a baseline, this oxygen delignification two phase reaction pathways will be determined for three commercially produced extended cook softwood pulps. Results of each phase of the reaction will be measured by kappa number, ISO brightness development, viscosity and wet Z-span. The pulps are thoroughly washed prior to oxygen delignification. Filtrates from the commercial pre - oxygen washing systems will be used to demonstrate the effects of carryover on the reactions. Two levels of carryover, 130kg COD/t and 200kg COD/t are studied. This part of the study will show how carryover affects each of the two phases of the oxygen delignification reaction, as well as the overall effect on selectivity. These results are measured by the same four variables used in the baseline. In one case, mill operating results are compared to study results. Effects of filtrate characteristics on each phase of the reaction are also studied. Variables measured are COD and residual alkali. It has been found that each filtrate variable has a distinct impact on both phases of the oxygen delignification reaction.