Industrial Process

In this stage, the objective is to separate the pulp fibers from the lignin disssolved during cooking.

In the alkaline wash, the pulp is washed in a counter-current flow in DD Washer rotational filters. The designation counter-current is applied because the pulp enters the first filter and progresses toward the final filter, while the water or condensate enters the final filter and progresses toward the first, thereby concentrating the black liquor (dissolved lignin and chemicals used in cooking) and leaving the fibers cleaned.

In the stage designated PRE-O, the pulp enters the first filter, passes through the first wash, and is pumped to the oxygen reactors. In the reactors, the pulp is maintained at controlled temperature and pressure, receiving quantities of oxygen and sodium hydroxide sufficient to dissolve the lignin within the fibers, thereby facilitating the bleaching stage.

After the PRE-O stage, the pulp goes through combined purification, where knots from the wood and small clumps of undercooked fibers are removed, leaving the pulp free of impurities. The washing stage is completed with two more DDW rotational filters, followed by the bleaching stage.