Treatment of cellulose material with additives while producing cellulose pulp

A method of continuously producing chemical cellulose pulp from comminuted cellulosic fibrous material slurry, with a yield or strength increase, comprising:

• (a) continuously treating the comminuted cellulosic fibrous material slurry with a solution containing yield or strength-enhancing additive;
• (b) after (a) continuously displacing liquor containing at least some of the additive from (a) in a continuous counter-current treatment zone;
• (c) continuously recirculating liquor containing displaced additive from (b) to the slurry in (a);
• and, after (b),
• (d) continuously treating the material with an alkaline cooking liquor, at cooking temperature, to produce a cellulose pulp with higher yield or strength than if (a) were not practiced.

A method of continuously producing chemical cellulose pulp from comminuted cellulosic fibrous material slurry, with a yield or strength increase, comprising:

• (a) pretreating the cellulose material with an alkaline liquid, with or without the presence of an additive;
• (b) after (a), removing at least some of the free liquor from the slurry;
• (c) after (b), treating the comminuted cellulosic fibrous material slurry with a solution containing yield or strength-enhancing additive;
• (d) displacing the majority of the additive from the slurry by substantially continuous counter-current treating thereof prior to bulk delignification;
• and
• (e) treating the material with an alkaline cooking liquor, at cooking temperature to produce a cellulosic pulp with a higher yield or strength than if (c) were not practiced.