content application_number US 78470785 A description in the following batch cooking methods with one and two cooking liquor exchanges are proposed for being able either to cook to kappa numbers in the range 20 25 or to cook to kappa numbers in the range 30 35 with raised viscosity level the basic layout for batch cooking with one liquor exchange is shown in fig1 to provide increased selectivity in delignification fig1 shows a flow chart block diagram for batch cooking by using the method according to the invention fig1 shows a digester in different stages 1 5 of the cooking cycle in stage 1 chips are filled and liquor is charged into the digester in stage 2 cooking phase 1 is performed in stage 3 displacement of strong liquor takes place in stage 4 the second cooking phase is performed and in stage 5 blowing is performed at the beginning of the cooking the digester 8 is charged with wood via line 9 and white liquor via line 10 and also with a certain amount of strong black liquor via flow 1 from the strong liquor tank 11 at 170 u00b0 c after completed cooking blowing is carried out to the blow tank 12 stage 5 at 100 u00b0 c from which the pulp is pumped via line 13 to the pulp washing plant 14 where the pulp is washed with washing liquor via flow 7 the filtrate is collected via line 6 in washing filtrate tanks 15 from which it is pumped via line 16 through a heat exchanger 17 and heat exchanged against strong liquor at 170 u00b0 c which is passed via line 18 at 90 u00b0 c to evaporation the washing filtrate thus heated is collected.