Process for continuously cooking chemical pulp in a digester system consisting of at least one vessel for impregnating and cooking comprising an inlet into which a mixture of chips and process liquid is fed. The chips are impregnated at a predetermined impregnation temperature Timp, and cooked at a predetermined cooking temperature Tcook, after which dissolved pulp is fed out at the outlet of the digester system. Process liquid which is continually extracted is retained outside the digester system during a dwell time, t, of at least 30 min, without any heating above 140 DEG , and thereafter returned to the digester system to a position which is substantially at the same level as the extraction, or downstream thereof, and thereby constitute part of the process liquid in the subsequent treatment zone. The process results in improved tear strength, beatability, bleachability and reduced colour reversion, and increased yield across the digester.
US 7217338 B2 (2007-05-15); JP 4292082-B2 (2009-07-08); EP 1454009 B1 (2010-06-30); BR 0214632-B1 (2013-06-04)