Importance

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Abstract

The invention discloses a method of continuous cooking cellulose fibrous material in a digester, said digester having a top and a bottom. The method of the invention comprises the steps of:—feeding a slurry comprising cellulosic fibrous material and cooking liquor into the top the digester,—feeding a first washing liquor into the bottom portion of the digester, which first washing liquor moves counter currently up through at least part of the digester,—removing pulp from the bottom of the digester,—feeding a second washing liquor into the center of the digester at least at the level of a first screen section,—feeding a third washing liquor into the center of the digester at the level of a second screen section, and—withdrawing the cooking liquor and the washing liquors from the first screen section and from the second screen section, which first screen section is arranged in a lower part of the digester and which second screen section is arranged below said first screen section. Thus, in accordance with the invention, a third washing liquor is added to the center of digester at the level of an additional, second extraction screen section arranged in the lower part of the digester. The method makes it possible to increase the production rate in the digester but still maintain or even increase the washing efficiency.

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First Claim