How Wood Chips Become Paper

The liquor cycle is also referred to as the kraft recovery process.

1. White liquor cooks the wood chips. The chemicals in white liquor help separate the useful wood fibers from lignin.

2. Black liquor is collected after cooking. It contains the dissolved wood material, including lignin, and the pulping chemicals.

3. Black liquor is concentrated and burned to separate the chemicals from the dissolved wood material. Burning the dissolved material produces useful energy that powers the mill, while the leftover chemicals are used to make green liquor.

4. The leftover chemicals become green liquor by being dissolved in water.

5. Green liquor becomes white liquor again. The green liquor is treated with lime to regenerate white liquor, allowing the mill to reuse the chemicals.

6. The cycle repeats, allowing the mill to reuse chemicals continuously.