Method and a device for preparing cellulose pulp

Abstract

A method and an apparatus for preparing cellulose pulp, in which a lignin-containing raw material is impregnated with impregnation liquor and the impregnated raw material is cooked. The black liquor obtained by cooking is concentrated in an evaporation plant integrated in a chemical recovery plant. In the impregnation, the lignin-containing raw material is impregnated with a circulating alkaline impregnating liquor, which impregnating liquor is concentrated by evaporating water from it in at least one evaporator unit of the evaporation plant arranged in the chemical recovery plant of a pulp mill.

Description

CROSS REFERENCES TO RELATED APPLICATIONS [0001] This application claims priority on Finnish Application No. 20041288, filed Oct. 4, 2004, and Finnish Application No. 20055289, filed Jun. 6, 2005, the disclosures of which are incorporated by reference herein. STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT [0002] Not applicable. BACKGROUND OF THE INVENTION [0003] The invention relates to a method for preparing cellulose pulp and to an apparatus for implementing the aforementioned. [0004] The purpose of pulping is to remove, from a lignin-containing raw material, the lignin which binds fibers to each other, and to detach the fibers from each other so that they can be utilized in the manufacture of cellulose and / or paper. When wood is used as the raw material, cooking is preceded by chipping of the raw material, i.e. chopping of the wood to the optimal size required by the pulping process. In sulphate cooking, or so-called kraft pulping, the...

AI Technical Summary

Benefits of technology

[0024] In addition to the numerous advantages mentioned above, the invention has the advantage that the hydrogen sulfide concentration of the impregnation liquor to be used in the impregnation stage can be raised as high as possible, compared to the hydrogen sulfide concentration of white liquor, wherein the yield from the cooking stage following the impregnation stage is improved. Furthermore, thanks to the reactions between lignin and sulfide in the impregnation stage, the bulk step of pulping becomes faster. Moreover, less water is conveyed with the impregnated chips into the cookin

Problems solved by technology

In particular, the thickness of a chip affects the distance and rate of penetration of chemicals into the central parts of the chip.

If the impregnation is insufficient and the rate of raising the temperature is too high, delignification will only take place in the surface layers of the chips, and the alkali concentration will decrease before it reaches the inner parts of the chips.

Furthermore, undesired reactions of condensation of lignin will be possible in the areas with an alkali deficiency, and the separation of the fibers will be incomplete.

However, this method only provides. a relative increase in the concentration of hydrogen sulfide ions when compared to the content of hydroxide ions, and the absolute hydrogen sulfide concentration is not necessarily very high compared to white l

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