Continuous process for digesting cellulosic material

Claim 1

IN A CONTINUOUS PROCESS FOR DIGESTING CELLULOSIC FIBROUS MATERIAL INCLUDING THE STEP OF: CONTINUOUSLY CHARGING CELLULOSIC FIBROUS MATERIAL INTO ONE END OF AN ELONGATED DIGESTER; IMPREGNATING THE CELLULOSIC FIBROUS MATERIAL WITH DIGESTING LIQUOR ADJACENT SAID ONE END OF THE DIGESTER, DIGESTING THE IMPREGNATED MATERIAL BY TREATING THE MATERIAL WITH HEATED DIGESTING LIQUOR WHILE PASSING IT THROUGH THE CENTRAL PORTION OF THE DIGESTER; WASHING THE MATERIAL ADJACENT THE OTHER END OF THE DIGESTER; AND DISCHARGING THE DIGESTED MATERIAL FROM SAID OTHER END OF THE DIGESTER; THE IMPROVEMENT WHICH COMPRISES CONDUCTING THE DIGESTING STEP IN TWO STAGES BY DIGESTING THE CELLULOSIC FIBROUS MATERIAL IN A FIRST DIGESTING ZONE IN THE CENTRAL PORTION OF THE DIGESTER WITH HEATED DIGESTING LIQUOR FLOWING THROUGH THE FIRST DIGESTING ZONE CONCURRENTLY WITH THE CELLULOSIC FIBROUS MATERIAL; DIGESTING THE CELLULOSIC FIBROUS MATERIAL IN A SECOND DIGESTING ZONE IN THE CENTRAL PORTION OF THE DIGESTER WITH A DIFFERENT DIGESTING LIQUOR FLOWING THROUGH THE SECOND DIGESTING ZONE COUNTERCURRENTLY WITH THE CELLULOSIC FIBROUS MATERIAL; SEPARATELY STRAINING OFF THE RESPECTIVE SPENT DIGESTING LIQUORS FROM THE TWO DIGESTING ZONES IN AN INTERMEDIATE ZONE THEREBETWEEN, THE STRAINING BEING CONDUCTED SIMULTANEOUSLY AND CONTINUOUSLY IN CLOSELY SPACED SEPARATING AREAS WITHIN THE INTERMEDIATE ZONE; WASHING THE DIGESTED CELLULOSIC FIBROUS MATERIAL FLOWING THE SECOND DIGESTING STEP WITH WASH LIQUD FLOWING COUNTERCURRENTLY WITH THE CELLULOSIC FIBROUS MATERIAL, THE WASH LIQUID BEING STRAINED OFF TOGETHER WITH SECOND STAGE DIGESTING LIQUOR, AND THEREAFTER DISCHARGING THE CELLULOSIC FIBROUS MATERIAL.