Process and requirements of pulping and papermaking

Process and requirements of pulping and papermaking
Time: 2022-07-26 Source: Wuhan Bonnin Technology Ltd.

The pulping and papermaking process is the process of dispersing the fiber raw materials into single fibers. The purpose is to dissolve the lignin in the raw materials and increase the specific surface area of ​​the fibers. The process and requirements of pulping are divided into:

1. Sawing: The logs must be sawn into a certain length to meet the requirements of the subsequent sections. The chipper requires the log length to be 2-2.5m, and the grinder requires the log length to be 0.6-1.2m.

2. Peeling: Due to the low fiber content and high impurity content of the bark, the cooking efficiency will be reduced, the consumption of cooking drugs will be increased, the dust in the pulp will increase, and the strength will decrease. Therefore, when producing pulp with higher quality requirements, it is generally required to remove the outer bark.

3. Removing knots: In order to avoid the influence of knots on the quality of the grinding stone and wood pulp during wood grinding, the wood segments sent to the grinder need to remove the knots.

4. Chipping: In order to meet the production needs of chemical wood pulp cooking and wood chip grinding, logs must be chipped. The chipped wood chips should be uniform in length, thickness and neat. The general specifications of wood chips are: 15--20mm long, 3--5mm thick, and the width is not limited, but it is hoped that it does not exceed 20mm. After chipping, the round screen should be screened, and the qualified rate of log wood chips is required to be greater than 85%.

5. Pulping: It refers to the production process of using chemical methods or mechanical methods or a combination of both methods to decompose plant fiber raw materials into natural pulp (unbleached pulp) or further bleaching into bleached pulp.

6. Washing: After the fiber raw materials are cooked, nearly 15-50% of the substances are dissolved in the cooking liquid. The cooking liquid discharged at the end of cooking is collectively referred to as waste liquid. The purpose of washing is to fully wash the pulp and extract the cooking liquid with a higher concentration and temperature for the alkali recovery process to recover organic or inorganic substances in the waste liquid. Chemical pulp still contains undecomposed components after washing. Coarse fiber bundles, groundwood pulp also contains coarse wood strips, large wood chips and coarse fiber bundles. In addition, during the collection, transportation, storage and production of raw materials, mud, fly ash, iron wire, plastic and other debris will also enter. These substances not only affect the quality of the paper, but also damage the machinery and equipment, making the production not smooth. Therefore, the above impurities must be removed by screening and purification.

7. Bleaching: The main purpose of the bleaching process is to remove the colored substances in the fiber to obtain pulp with a certain whiteness and appropriate physical and chemical properties.