High yield cooking, oxygen delignification and ozone for high yield bleached pulp

Low Kappa cooking technology such as RDH and EMCC have gained a lot of momentum in the last 5 years. With such methods it was common to see Kappa numbers after cooking down from the old standard of 28/30 to as low as 18 to 20. Conventional practices then combined extended cooking with an oxygen delignification stage and ECF bleaching sequence, where the Kappa number and bleaching chemical costs are significantly reduced from a conventional cook (30)D(0)EopDED. Previous papers by Homer et. al. have suggested that this may not be the optimum cost approach when wood and chemical costs are considered. Lower bleaching costs resulting from significantly reduced Kappa number to the bleach plant may be offset by higher wood cost resulting from a lower wood yield from the pulping and prebleaching processes. Oxygen delignification or Mini-O-2, Ozone bleaching and polysulphide AQ are few of the technologies available today and proven to the industry which can be applied effectively to increase bleached pulp yield. Oxygen is known for its improved selectivity within a certain kappa range, Ozone in D/Z allows for higher Kappa pulp entering the bleach plant without increasing ClO2 requirement and maintaining strength properties, and PSAQ for enhancement of cooking yield.