screen sc 3 after use in a cooking zone in a subsequent digester 6 which impregnation fluid bl has an alkali level of at least 15 g l the amount of impregnation fluid bl that is added to the vessel 3 lies between 5 10 m 3 adt preferably between 7 9 m 3 adt where u201c adt u201d is an abbreviation for u201c air dry tonne u201d of pulp the temperature of the impregnation fluid bl in the feed line 41 maintains a temperature of 115 150 u00b0 c and the chips level ch lev lies at least 1 2 meters over the fluid level and preferably 3 5 meters over the fluid level liq lev in order to facilitate drenching of the chips down into the impregnation fluid where the chips are thoroughly impregnated the weight from the chip volume above the fluid level assists in drenching the chips even if some residual air may be caught in the chips given non steam treated chips that maintain 25 u00b0 c with their naturally occurring moisture level 5 tonnes of fluid that maintains 139 u00b0 c are required in order to establish a temperature of approximately 115 u00b0 c in the chips mixture at the fluid level if a temperature of 100 u00b0 c is to be established in the chips mixture given the same basic conditions 5 tonnes of impregnation fluid that maintains 120 u00b0 c is required by adding the hot impregnation fluid in association with the fluid level ch lev most if not all the air present in the chips will be flashed out and the chips will sink in the impregnation fluid a line 42 withdraws spent impregnation fluid and steam condensate i.