Pretreatment of chips with white liquor prior to a treatment with black liquor
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United States of America Patent
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-
Sep 18, 2007
Grant Date -
May 19, 2005
app pub date -
Dec 13, 2002
filing date -
Dec 14, 2001
priority date (Note) -
Expired
status (Latency Note)
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Abstract
The method is for the manufacture of cooked cellulose pulp in which the starting material, preferably chips, undergoes a successive increase in temperature towards cooking temperature. This is done while the chips are first treated in a pre-treatment zone in which the main part, greater than 50%, of fresh white liquor necessary for the cooking stage is added, after which this alkali-rich treatment fluid is withdrawn and replaced to a major extent by black liquor. The alkali-rich treatment fluid that has been withdrawn after the pre-treatment stage is then added to the cooking stage, which is why the addition of fresh white liquor to the cooking stage is reduced to an equivalent amount. Maximal yield-enhancing effect is obtained using poly-sulphide-rich white liquor during the pre-treatment at a temperature in the interval 60.+-.40.degree. C. and retention time in the interval 2-60 minutes, preferably 2-10 minutes.
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