Patent ID: 6159336
Filing Date: 2000-12-12
Classification: D21C

Abstract:
A method for continuously producing pulp, comprising the steps of:providing a finely divided fiber material, a transport fluid and an impregnation zone;providing a digester to facilitate a cooking reaction, the digester having a separator at a top portion of the digester and a first screen girdle section disposed therein, the separator having a separation zone and a cooking liquor inlet zone, the digester having at least one cooking zone;providing an amount of cooking liquor required for the cooking reaction;transporting the fiber material and the transport fluid to the impregnation zone;heating and impregnating the fiber material disposed in the impregnation zone;passing the heated and impregnated fiber material from the impregnation zone to the first cooking zone;separating the transport fluid from the heated and impregnated fiber material in the separation zone of the separator of the digester;supplying a first portion of the amount of cooking liquor at the cooking liquor inlet zone of the separator of the digester;obtaining a first effective alkali concentration in the first cooking zone that is at least 35 grams per liter;passing the fiber material and the cooking liquor through the first cooking zone;cooking the fiber material in the first cooking zone;withdrawing a first amount of a spent liquor from the first screen girdle section in the digester, the spent liquor having an effective alkali level of at least 13 grams per liter; andtransferring a substantial portion of the first amount of the spent liquor withdrawn at the first screen girdle section in the digester to the impregnation zone.