Black Liquor Treatment in Paper Pulping Process. Part 1

Hello, dears. This article is mainly about black liquor treatment in the paper pulping process. In this part I will introduce what is black liquor, the property of black liquor and what is the pollution that can be caused by black liquor. In the second part, I will explain how to deal with the environmental unfriendly black liquor issues. The second part will be posted after the Chinese New Year vacation. And There, no matter which country you are in now, I send you my best wishes.

What is black liquor

Black liquor refers to the washing liquid of pulp after digesting and washing in the process of sulfate or alkaline pulping process. The black liquor is black, which contains the inorganic substances in the cooking agent, the degradation products and organic acids of lignin, hemicellulose and cellulose, which are dissolved from the plant fiber raw materials. Inorganic substances include free sodium hydroxide, sodium sulfate, sodium sulfide, sodium carbonate, sodium and silica, which are combined with organic compounds.

Black liquor property

• Chemical property: Black liquor is colloidality, corrosivity and easy to oxidize.
  1. The colloidal substance in the black liquor is mainly composed of resin acid and fatty acid salt and hydrated glass colloid. When the gel enters the evaporator, it will accelerate the formation of scale and reduce the heat transfer coefficient.
  2. The causticity of black liquor is mainly due to its secondary steam and its condensed water containing volatile organic acids or various acidic sulphides. Therefore, it is highly corrosive to the equipment exposed to the secondary steam and its condensate, such as the outer wall of the heating tube of the after-effect steam chamber, the discharge system of the dirty condensate and the condenser, etc. The higher the vulcanization, the more corrosive it is.
  3. Easy oxidation of black liquor of sex refers to the black liquor after contact with the air of the inorganic sulphide and organic sugar easy to oxidation, thus reduce black liquor pH value, viscosity, easy to scale formation in the process of evaporation.
• physical property: The concentration of black liquor (solid content) is an important index to check and control evaporation.It is generally expressed in terms of baume.
• Black liquid viscosity：The high viscosity of black liquor is unfavorable to evaporative production, high viscosity leads to low heat transfer efficiency. Reducing measure is to raise the effective alkali content or raise the black liquid temperature.

What is the pollution of black liquor

The paper mill produces three kinds of waste water according to the process:

1. one is the pulping and cooking liquid, namely the black liquor of papermaking;
2. The second is the separation of black liquor after the washing, selection, floating water, also known as the middle water;
3. Three is the white water on the paper machine, white water can be processed and reused.

In fact, the water in the middle section is the part that is not completely extracted from the black liquid, which is usually less than 10% of the total amount, and the pollutants contained in the black liquor account for more than 90% of the total pollution emissions of the whole plant.

Therefore, paper black liquor is the main part of paper mill pollution.

• Black liquor contains a large amount of suspended solids, organic pollutants and toxic substances, which can cause serious pollution directly into the water body.
• The main hazard is that the waste water containing a large amount of fiber, pigment and inorganic salt will blacken the water body and have a special stench.
• The biochemical oxygen consumption (BOD) of paper black liquor containing high concentration of organic pollutants (BOD) is up to 5000-40000g/L, which will consume the dissolved oxygen in water and affect the water quality.
• The alkaline substances in the black liquor can cause the pH value of water body to rise sharply and destroy the balance of water environment.

To process the black liquor, CNBM now can provides the most efficient ways for you. In recent years, CNBM black liquid treatment technology has been further improved and developed. welcome the domestic and foreign customers to contact us, we will wholeheartedly provide you with quality service!