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:: Home > The Mills > Pulp & Papermill > Pulp Mill

To make pulp, wood chips are broken up into individual wood fibers. This can be done by cooking the wood at high temperatures with a mixture of water and chemicals, known as white liquor. White liquor contains sodium hydroxide and sodium sulfide, both of which soften the wood as it cooks.

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chip handling pulp mill bleaching paper mill products transport

The Kamyr digester at the left is a "continuous digester," since the wood chips constantly flow into the top and leave the bottom as processed pulp. This digester can cook up to 560 tons of pulp each day, and wood is retained in the Kamyr for 4-6 hours.

Other digesters are "batch digesters," as wood is added, processed, then dumped in batches. Three batch digesters at St. Helens process 320 tons per day, in batches that cook for one hour.

Once the pulp has been processed, it can be sent through a blowtank (at right) to separate the fibers.

Making sure all of this wood-processing runs smoothly is no easy business. Nowadays computers are used to monitor every step of the process.
After leaving the digester, the pulp is washed to remove residual chemicals.
After digesting the wood chips, we have freshly cooked, dark pulp, know as "brown stock." Brown stock is then moved by pipes to the bleach plant.