Industrial Process

The process of pulp production begins with the handling of the raw material which occurs in the wood yard, where the logs are received from the forest with the bark removed. The logs are taken to a storage yard or directly to the chipper according to a pre-determined sequence.

The logs are unloaded onto feeding tables, washed, and carried by conveyors to the chipper. A 12-blade rotating disc transforms the logs in a few seconds into small chips, which are deposited on a chip yard.

Chipping is carried out with a view toward the ideal chip size for the cooking stage. Separation of the chips by size occurs on a vibrating sifter before they enter the contnuous digester’s chip silo. Chips not meeting specifications are removed, to be utilized as fuel for the biomass vessel.

Chips within specifications are transported to the continuous digester’s chip silo on conveyors with metal detection systems to avoid damage.

In this stage, the objective is to dissolve any lignin present between the wood fibers. These fibers are the actual cellulose pulp.

The wood chips are submitted to chemical action with white liquor (sodium hydroxide plus sodium sulfide) and steam in the contnuous digester (pressure vessel) with controlled temperature, pressure and retention time.

After cooking, the pulp undergoes the first wash in the continuous digester and is then discharged into a discharge tank (blow tank), where it is stored for transfer to the next stage in the 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.

Pulp’s natural color is white, but during removal of lignin in the early stages of production it is changed to light brown by the oxidation of organic matter in the wood.

To remove this coloration and return it to white, the pulp is submitted to chemical treatment with oxidizing agents in reactors with controlled temperature, pH and retention time. This process is carried out in 3 stages (Ado/EP/D), and at the end of each stage the pulp is washed in DDW rotational filters in order to remove colored oxidized compounds.

 The objective of this stage is to mold and dry the sheets of pulp and to package them in bales.