Patent ID: 6350348
Filing Date: 2002-02-26
Classification: D21C

Abstract:
A method of cooking comminuted cellulosic fibrous material to produce cellulose pulp in at least one batch digester comprising substantially sequentially:(a) introducing the material to the digester; (b) introducing a first liquor having a first effective alkali concentration to the digester; (c) treating the material in the digester with the first liquor; (d) displacing first liquor from the digester with a second liquor having a second effective alkali concentration, to produce a third liquor, displaced from the digester, having a third effective alkali concentration lower than the first effective alkali concentration; (e) treating the material in the digester with the second liquor; (f) displacing the second liquor from the digester with a fourth liquor having a fourth effective alkali concentration to produce a fifth liquor, displaced from the digester, having a fifth effective alkali concentration, lower than the second effective alkali concentration and between 20-40 g/l, expressed as NaOH; and (g) removing the treated material from the digester; and wherein the fifth liquor comprises at least some of the liquor to be used as the first liquor in (b) for a subsequent batch, and repeating (a)-(g) for the subsequent batch in the same or a different digester.