Patent ID: 6699357
Filing Date: 2004-03-02
Classification: D21C

Abstract:
A process for a continuous cooking of wood chips at elevated pressure and temperature in a vertical digester for production of chemically dissolved pulp, comprising:providing the digester with a top and a bottom and introducing the wood chips and a cooking liquor at the top of the digester; establishing a cooking zone in the digester; maintaining a mean cooking temperature in the cooking zone at a temperature of between 135Â° C. and 180Â° C.; maintaining the mean cooking temperature for a wood chip dwell time of at least 45 minutes; extracting used cooking liquor from the digester and away from a cooking process via an extraction arrangement disposed between a pretreatment system and the bottom of the digester; conveying a first quantity (Q1) of the extracted used cooking liquor to a unit; discharging pulp from the bottom of the digester into a line; feeding the pulp in the line, at a pressure level that does not induce cooking of the pulp, to a pressure diffuser; expelling a liquid of the pulp to obtain a filtrate having a high temperature being not more than 20Â° C. below the mean cooking temperature; extracting a first portion of the liquid disposed in the pressure diffuser and conveying the first portion to the recovery unit, the first portion of the liquid representing a second quantity (Q2) of the used cooking liquor extracted from the process, the first quantity (Q1) and the second quantity (Q2) representing a total quantity of used cooking liquor extracted from the process; conveying a second portion of the liquid back to the bottom of the digester; and regulating a ratio of between the first quantity (Q1) and the second quantity (Q2) of the used cooking liquor so that (Q2)>(Q1).