Patent ID: 6123807
Filing Date: 2000-09-26
Classification: D21C

Abstract:
A method for continuously producing pulp, comprising:providing a finely divided fiber material, a transportation liquid and an impregnation zone, the impregnation zone maintaining a cooking pressure;providing a digester having a top portion and a bottom portion and at least one strainer girdle disposed therein, the digester being adapted to facilitate a cooking reaction, the digester having a concurrent cooking zone at the top portion of the digester, the concurrent cooking zone having a beginning and an end;providing the digester with a total amount of cooking liquor;mixing the finely divided fiber material with the transportation liquid to form a slurry;while mixing the finely divided fiber material, transporting the slurry to the impregnation zone;while transporting the slurry, prevailing the cooking pressure in the impregnation zone;transferring a hot black liquor to the impregnation zone;while transferring the hot black liquor, heating the fiber material disposed in the impregnation zone to a first temperature that is below 140 degrees Celsius and thoroughly impregnating the fiber material by exposing the fiber material to the hot black liquor;while heating the fiber material, passing the fiber material through the impregnation zone in a direction that is concurrent with a flow direction of the hot black liquor;while passing the fiber material through the impregnation zone, separating and withdrawing a substantial portion of the transportation liquid from the slurry in the digester;while separating and withdrawing the transportation liquid, transferring the heated and thoroughly impregnated fiber material from the impregnation zone to the concurrent cooking zone;while transferring the heated and impregnated fiber material, supplying at least 60% of the total amount of the cooking liquor to the concurrent cooking zone of the digester;while supplying the cooking liquor, obtaining a first level of effective alkaline that is at least 35 grams per liter at the beginning of the concurrent cooking zone;while obtaining the first level of effective alkaline, withdrawing spent liquor, that have passed through the concurrent cooking zone of the digester, at the strainer girdle of the digester, the spent liquor having an effective alkali level of at least 13 grams per liter;removing pulp from the bottom portion of the digester; andmaintaining a second temperature in the beginning of the concurrent cooking zone that is higher than the first temperature of the impregnation zone, the second temperature being below 160 degrees Celsius.