Two-stage continuous digestion with removal of liquor in first stage and recirculation of liquor in second stage

Claim 1

A TWO-STAGE CONTINUOUS PROCESS FOR PRODUCING RELATIVELY HIGH QUALITY KRAFT PULP FROMA CELLULOSIC STARTING MATERIAL IN THE FORM OF CHIPS HAVING ALKALI-SOLUBLE LIGNIN COMPONENT AND A CELLULOSE COMPONENT COMPRISING THE STEPS OF FIRST DIGESTING SAID CHIPS IN A FIRST ALKALI COOKING LIQUOR FOR A PERIOD OF TIME SUFFICIENT TO FORM A PARTIALLY COOKED CHIP MASS IN WHICH A PREDETERMINED PORTION OF THE ALKALI-SOLUBLE LIGNIN COMPONENT OF AISA CHIP MASS IS DISSOLVED RESULTING IN A SUBSTANTIAL INCREASE IN THE DISSOLVED LIGNIN CONTAINED IN SAID FIRST COOKING LIQUOR, CONTINUOUSLY ADVANCING SAID CHIPS IN A GENERALLY HORIZONTAL PATH WHILE MAINTAINING AN ELEVATED TEMPERATURE AND EQUIVALENT PRESSURE AND PROVIDING A VAPOR PHASE ABOVE SAID COOKING LIQUOR, RECIRCULATING SAID FIRST COOKING LIQUOR THROUGH SAID CHIP MASS DURING SAID FIRST DIGESTING STEP TO MAINTAIN THE CONCENTRATION OF SAID FIRST COOKING LIQUOR SUBSTANTIALLY UNIFORM, REMOVING A SUBSTANTIAL PORTION OF SAID FIRST COOKING LIQUOR AND THE DISSOLVED LIGNIN FROM SAID PARTIALLY COOKED CHIP MASS, FURTHER DIGESTING SAID PARTIALLY COOKED CHIP MASS WITH A SECOND ALKALI COOKING LIQUOR HAVING A RELATIVELY LOW CONCENTRATION OF DISSOLVED LIGNIN THEREIN, CONTINUOUSLY ADVANCING SAID PARTIALLY