wall section that has been extended downwards the additional extra nozzles 34 are evenly distributed around the circumference of the digester and they are present in such a number that the distance around the circumference between neighbouring extra nozzles is less than 3 meters preferably less than 2 meters it is appropriate that the nozzles have an opening that delivers a concentrated jet into the column of pulp but they may have openings that are oval or slits in the direction around the circumference addition of fluid may in one extreme variant in which it is desired to achieve greater volumes of added fluid between the extra strainer section and the lower strainer section also take place through what is essentially one single continuous slit that runs around the circumference it is advantageous for achieving the best penetration effect into the column of pulp that the slit of the openings of the nozzles are subject to a controlled drop in pressure for the establishment of a high injection velocity of fluid into the column of pulp the lower strainer section 2 is constituted by at least one row of strainers preferably by at least two rows of strainers as is shown in fig2 where each row of strainers 3 a 3 b consists of strainer plates or rod strainers arranged in the direction of the circumference around the digester a collecting channel 20 is arranged at each row of strainers 3 a 3 b for the cooking fluid that has been withdrawn.