TREATING PULP WITH OXYGEN

P 73 4686 TREATING PULP WITH OXYGEN ABSTRACT OF THE DISCLOSURE A wood pulp slurry is treated with oxygen in a mill with little change to the process or structure of the mill. No special pressure tanks are required. The consistency of the pulp need not be altered for the treatment step. It may be treated at the usual process consistency of the pulp; e.g., it may be treated at the usual consistency of the pulp leaving a washer (91'') or subsequent steam mixer (106) without additional dewater-ing or additional dilution. The oxygen is added into a closed section of the system so that it cannot immediately vent to the atmos-phere. Alkali should also be present when the oxygen is mixed with the slurry. The mixing should occur near to the point of oxygen addition. The oxygen is inserted into the pulp slurry and mixed with the pulp slurry between a washer (91'') and the subsequent storage tank (110'). The mixing occurs in a relatively small mixer (108) that intensively mixes the slurry and gas. The mixer has a mixing zone with a swept area of 10,000 to 1,000,000 square meters per metric ton of oven-dry pulp. A preferred range is 25,000 to 150,000 square meters per metric ton of oven-dry pulp and an optimum range of around 65,400 square meters per metric ton of oven-dry pulp. Specific mixer designs are disclosed.