Black Liquor Treatment in Paper Pulping Process. Part 2

Last week, we have talked about what is the black liquor and what kind of pollution can be caused by black liquor. This week, we'll talk about how to process black liquor. CNBM is pretty mature in black liquor treatment. If you need paper pulper machines or equipment, or you have any questions about paper pulping, please leave us messages and our professional staff will give you a free consultation online.

How to process black liquor

Handling of paper-making black liquor is the key to the paper industry wastewater treatment, at present, the commonly used papermaking black liquor treatment technology are alkali recovery method, flocculation precipitation, membrane separation, acid analysis method, aerobic activated sludge process and biological technology method, etc. Among them, alkali recovery method is the most widely used paper black liquor processing method.

Combustion of alkali recovery

Alkali recovery technology is a mature technology of black liquor processing in papermaking, which has been widely used in various regions. According to different working principle, it can be divided into combustion method, electrodialysis method and black liquid gasification method.

The complete process of combustion method can be divided into four processes: extraction, evaporation, combustion, causation - lime recovery. The basic principle is concentrating black liquor in the combustion furnace, then the organic sodium salt will turn into inorganic sodium salt, then add lime to it and it will turn into sodium hydroxide, to achieve the goal of recovery of alkali and heat energy.

Extracted from black liquor from pulp, wood pulp (grass) dilute black liquor concentration is low, it must be get rid of most of the water by evaporation system, concentration to the concentration of 45% to 80%, then the concentrated black liquor is sprayed into the alkali recovery boiler combustion chamber of a stove or furnace, heat from the burning of black liquor can be used to process or power generation. Black liquor of organic sodium salt in the reaction furnace into molten sodium carbonate, and the supplement of glauber's salt reduction into sodium sulphide, the melt from a base at the bottom of the furnace, dissolves to form green liquor containing a small amount of iron ions. The obtained green liquor reacts with lime, and the sodium carbonate is caustic to sodium hydroxide. The clarified liquid is called white liquid and can be reused for pulping and cooking. The white clay produced by causation is calcined at high temperature, and lime can be recovered for causticization.

The recovery process technology of combustion method is mature and stable, but the engineering investment is larger, which is suitable for larger paper enterprises. Currently, the treatment of black liquor mainly adopts combustion method to recover alkali. But in the alkali recovery susceptible to black liquor combustion method, the interference of silicon components: silicon dioxide and alkali in black liquor generated sodium silicate, easy formation of scaling in the combustion process, and affected the alkali recovery process smoothly. The content of silicon in wood pulp is low, so the alkali recovery is successful, and the alkali recovery can reach 95-98%. However, due to the shortage of forest resources in China and the relatively abundant grass resources, the paper industry structure is formed with straw pulp papermaking, and the high silicon content in the black liquor of grass slurry affects the effect of alkali recovery.

Electrodialysis method

The process of electrodialysis usually adopts the circulating process, the black liquid is circulating through the anode chamber, and the dilute lye is circulated through the cathode chamber. Under the action of the direct current field, Na+ enters the cathode chamber through the positive membrane, and produces the NaOH with electrolysis, which can be used to recover the alkali. The anode chamber black liquor is constantly acidified due to the electrolysis of H+, and in a certain degree, most of the lignin precipitation is precipitated out. Electrodialysis method is simple in process, easy to operate, less investment in equipment and easy to automate. In order to improve the alkali recovery and reduce the power consumption, the electrode and diaphragm need to be improved.

Black liquor gasification

In addition to the above two methods, black liquor is widely used in foreign countries. The principle is to vaporize the black liquid in a high temperature and fast reactor and convert the organic matter into a clean fuel gas for the gas turbine. Black liquor gasification is more effective than traditional combustion recovery, and it is a promising technology for the energy production and recycling of pulp and paper industry.

The paper pulp system of CNBM improves the black liquid pollution

Paper black liquor has caused serious pollution to the environment and also wasted valuable resources. With continuous research and practice, CNBM has found effective ways to recycle the alkali recovery and other resources, so that the comprehensive utilization and pollution control of paper black liquor has achieved good results.

In recent years, CNBM black liquid treatment technology has been further improved, welcome the domestic and foreign customers to contact us, I will wholeheartedly provide you with quality service!