CONTINUOUS COOKING WITH COOL IMPREGNATION AND DOM CONTROL

摘要

A method of treating wood chips allows chemical pulp (e.g. kraft pulp) to be produced having enhanced fiber strength properties. In a first zone or stage the chips are cool impregnated (e.g. at a temperature of about 60-120 ~C) with a first alkali-containing liquid (25-35 g/l expressed as NaOH). In the top of a continuous digester (13) in a second zone or stage (between the screen assemblies 17, 25) the chips are then treated with a second alkali-containing liquid having an alkali concentration at least 5 g/l less than the first liquid (e.g. 10-20 g/l) and a temperature of between about 120-160 ~C (e.g. 130-150 ~C). An extraction (25) typically takes place to effect the change in treatment zones. After the second zone the chips are cooked in a cooking zone or stage (32) at about 140-180 ~C (e.g. 150-170 ~C), and at a higher temperature than in the second zone.