BLEACHING WOOD PULP

Wood pulp is bleached in a process which includes passing pulp slurry from a chlorine tower through a washer to a downflow extraction tower which is open to the ambient atmosphere. Caustic and steam are supplied to the extraction tower as is dilution water which is introduced into the lower portion thereof. Oxygen is dissolved in the dilution water which may be at least partially comprised of recycled washer filtrate. This addition of oxygen to the dilution zone of an extraction stage enables the consumption of chemicals such as hypochlorite and/or chlorine dioxide to be reduced while still meeting required levels of pulp brightness and strength. Oxygen may be added to the extraction or other alkaline stages of a bleaching process.