Recycling method of alkaline pulping by-product

Abstract

The invention relates to a recycling method of an alkaline pulping byproduct. Lignin and alkali in black liquor are separated through step-by-step multiple acidification concentration. The method comprises the following steps: neutralizing the black liquor by using flue gas to reduce the pH value of the black liquor, separating out lignin in the black liquor, greatly improving the concentration of the lignin, enabling the lignin in the black liquor to form large particle precipitates with compact structures by using sulfuric acid and/or a flocculating agent, filtering out the lignin, and further dehydrating the lignin to obtain a lignin product. And causticizing the residual clear liquid after the lignin is stripped by lime, respectively cooking the plant raw material and washing the paper pulp, and using the obtained insoluble calcium salt as a building material. The method can be used for alkaline pulping of woody plants and non-woody plants. And technical support is provided for realizing net zero emission of carbon dioxide.

Description

technical field [0001] The invention relates to the processing and utilization technology of by-products of papermaking, in particular to a method for recycling by-products of alkaline pulping. technical background [0002] At present, the alkali recovery furnace is used to recover caustic soda and lignin in the production of pulp by the alkali process. Although this method does not have direct black liquor discharge, the alkali recovery furnace requires huge investment, long installation and commissioning period, and high operating cost, so that the small pulping enterprise with an annual output of 50,000 tons of pulp cannot implement it and has to close it. Even large and medium-sized pulp mills have the ability to implement this technology, the large amount of black liquor formed by cooking plant raw materials and washing pulp is concentrated by evaporation to remove water, and then burned to remove lignin to recover caustic soda. Using this method not only has low utili...

AI Technical Summary

Problems solved by technology

Using this method not only has low utilization value of lignin, but more importantly, the evaporation and concentration of black liquor needs to consume a large amount of fuel, so that its operating cost is very high. At the same time, the combustion of fuel and black liquor also generates a large amount of carbon dioxide. At present, these Carbon dioxide is directly emitted into the atmosphere and pollutes the air, which is completely contrary to the goal of "double carbon"