Papermaking process should strengthen washing, screening and purification

After chemical cooking of plant fiber raw materials, 50~85% pulp is obtained, and nearly 15~50% of the substances are dissolved in the cooking liquid. The cooking liquid discharged from cooking is collectively referred to as waste liquid.

The purpose of washing is to separate the waste liquid of the pulp to ensure the cleanliness of the pulp, and to create good operating conditions for the screening and bleaching of the next process. It is necessary to protect the washing waste liquid as much as possible to have a higher slurry, so as to facilitate drug recovery or comprehensive utilization. Therefore, it is necessary to use less water on the premise of ensuring the quality of pulp washing.

Screening is also an indispensable and important link in the pulping process. The cooked pulp contains 1~5% undissolved matter.
For wood pulp, it is mainly bark, knots, strips, wood chips, etc.; online consultation
For straw pulp, it is mainly grass knots, rattan seeds, etc. In addition, there are non-fibrous impurities such as sediment, gravel, iron filings, etc. customer service 1
According to the requirements of pulp quality, these fibrous and non-fibrous impurities must be separated and removed from qualified pulp fibers through screening and purification processes. customer service 2
The so-called screening refers to the use of certain mechanical equipment to remove fibrous impurities in the pulp. It can be divided into rough selection and selection. Purification is mainly to remove non-fibrous impurities. 4 Customer Service 3
For unwashed pulp, most of the waste liquid is free in the flow space between fibers, about 80-85%, and about 15-20% of the waste liquid exists in the fiber cell cavity and cell wall,by   during the washing process, most of the free waste liquid is relatively easy to separate out. It can be extruded by pressing force, which can be static pressure of washing or external mechanical pressure. For the waste liquid in the cell cavity and cell wall, it is not possible to rely on a simple extrusion method. Only the diffusion method is used, and the concentration difference between the washing water and the waste liquid is used to diffuse the dissolved substances contained in the waste liquid.

Therefore, the washing of pulp must use a variety of principles of action. Mainly diffusion, filtration, extrusion, etc. A certain kind of washing equipment is often based on one function process, and other functions are supplemented.
Although there are various insoluble impurities with different properties in the pulp, two principles are generally used to distribute these impurities:
The pulp is separated by sieving according to its size, shape, and shape, and this process is called pulp screening; the other is by gravity drop or centrifugal separation according to the proportion of impurities larger than that of fibers. A process called purification.
In the actual production process, two methods are often combined to constitute the technological process of pulp screening and purification.


Post time: Jan-12-2022