Oxygen delignification process is used for dissolving lignin by making use of the strong oxidant effect of molecular oxygen and oxydative degradation in alkaline medium. It has become a necessary process for the production of high brightness chemical pulp. At conditions of medium consistency, pulp is bleached using oxygen as the bleaching agent. This further reduces pulp kappa value. About 40% - 50% of the kappa value of the original coarse pulp can be decreased.