Papermaking White Water Closed, Resulting In Waste Accumulation, How To Do?

Mar 01, 2023

Technology collation

With the improvement of the closed circulation degree of the white water of paper machine, the accumulation and concentration of interfering anionic impurities in the wet part will be higher , and the problem of anionic waste will be more obvious, just like lipid in the blood, which needs to be dealt with in time.

Anionic wastes include hemi cellulose, lipophilic extract, lignin, neutral polysaccharide, charged polysaccharide, protein, etc. And colloidal particles are composed of extracts, carbohydrates, and lignins.

These substances are divided into two categories: dissolved and colloidal.

Dissolved and colloidal substances are the most important components in the closed cycle of papermaking wastewater.

Dissolved substance (DS) and colloidal substance (CS) in white water are collectively referred to as colloidal substance (DCS).

In papermaking system, the content of anionic garbage can be expressed by cationic demand CD of slurry filter.

DCS harm and source
The main harm caused by the accumulation of anionic waste is as follows:

① The anionic substance in DCS is the main component of anionic garbage, in high concentration, it will weaken the use of cationic additives.

② Colloids are viscous and easy to deposit, which is an important cause of secondary adhesive obstacles.

③ Excessive accumulation of DCS leads to deterioration of chemical environment of water system and abnormal operation.

④ Increaseing the water treatment load and chemical dosage, hinders the process water closed circulation and causes rot pulp.

On one hand ,DCS comes from soluble wood extract (small seed lignin, starch, sugar, etc.) ,resin and other natural substances, on the other hand, it comes from waste pulp mixed with adhesive substances. At the same time, the chemical additives added in the papermaking process and the fine fiber fragments in the pulp are also important components of DCS.

The geometric size of these substances is generally less than 10μm, so it is quite difficult to control, and the control object is limited to colloidal substances (CS).

Effect on paper property

After the system closed cycle, the anionic waste will directly affect the operation of paper machine and the quality of paper.

However, due to the different raw materials, types of paper and production conditions of paper mills, there is no unified evaluation standard for the effect of closed white water cycle on paper performance.

For newsprint, the breaking length, tensile strength, breaking index, elongation and binding force all decreased with the increase of DCS. In terms of optical properties, the whiteness decreases with the increase of pollutants, and the light scattering coefficient, light absorption coefficient and opacity generally increase with the increase of pollutants.

The results show that that CS has more influence on the breaking length of newsprint than DS.

For cardboard and packaging paper, the physical strength is not adversely affected, but has an improvement, cardboard break resistance and annular compressive strength indicators are rising, and the accumulation of oil substances in the white water system will greatly reduce the physical strength of the paper.

Measures to reduce "blood fat"

DCS is usually controlled by chemical methods in modern papermaking systems.

The most effective way to reduce the influence of anionic waste in papermaking system is to pretreat the pulp with anionic waste catcher (ATC) or fixating agent.

ATC is generally linear low molecular weight polymers with high positive charge density, including inorganic ATC and organic ATC, such as polyamine, polyethylenimine, polydiallyl dimethyl ammonium chloride and some inorganic aluminum compounds (aluminum sulfate, polyaluminum chloride, etc.).

These substances have a strong charge neutralization ability, can reduce the interference material to cationic requirements, so as to reduce the negative impact on cationic additives.

ATC forms small pairs with soluble anionic impurities through charge neutralization or adsorption bridging, which are retained and fixed on the fiber filler after flocculation.

It is generally added before pulp to other cationic additives, sometimes must be added as early as possible to control the cationic requirements of the system.

The type of ATC has an important influence on its use effect. Research shows that different ATC has different effects on colloidal substances and fine components. Organic ATC can effectively reduce the cationic demand on fiber surface. When reducing the cationic demand of interfering substances, organic ATC should be the first choice.

Compared with inorganic ATC, the biggest advantage of organic ATC is that it is not affected by pH value, has no effect on the paper system and small amount, the effect is obvious.

In addition, retention and fixation agents (neutralizing and fixing AT) can also be added to the network part, so that a part of CS is taken away with the page. Or by means of gas floating sand filter can make the clarification of water of dealing with solid content dropped to under five ㎎ / L, and then USES the membrane method or biological membrane method system processing, to remove the water dissolved organic matter and soluble salt.

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