METHOD FOR OXYGEN DELIGNIFICATION OF CELLULOSE PULP AT HIGH PRESSURE

摘要

The invention concerns a method for an improved oxygen delignification of cellulose pulp with a medium consistency, 8-16%. By pressurisation to a high pressure, greater than 15.0 bar, and by repeated mixing while maintaining the pressure, the fraction of dissolved oxygen can be kept at a high level throughout the complete process, such that a fraction as large as just over 20% of the total amount of oxygen added can be dissolved in the fluid phase, and such that the amount of oxygen in the fluid phase can be maintained at a high level throughout the complete high pressure section. The pressurisation takes place, according to the invention, by at least two pumps arranged in series, where the first pump is an MC pump with a fluidiser and with means of deairing, while subsequent pumps are either MC pumps without deairing or centrifugal pumps, where these subsequent pumps have a pumping efficiency that is at least 10%-20%, higher than that of the first pump. This ensures that the amount of oxygen that is dissolved in the fluid phase and that penetrates the cellulose fibres can be maintained at an optimal high value throughout the process, to give an improved delignification of the cellulose and that pressurisation can take place in an optimal manner.