Method and apparatus for maintaining a water balance during impregnation and digestion of cellulosic material

Claim 1

IN THE CONTINUOUS PULPING OF CELLULOSIC RAW MATERIAL WHEREIN SAID RAW MATERIAL IS SUBJECTED TO IMPREGNATION WITH AND IMPREGNATION LIQUOR CONTAINING AN AQUEOUS SOLUTION OF DIGESTING CHEMICAL IN AN IMPREGNATION SYSTEM THEREBY TO IMPREGNATE SAID MATERIAL WITH DIGESTING CHEMICAL IN A PREDETERMINED WEIGHT RATIO AND WHEREIN WATER ENTERS SAID IMPREGNATION SYSTEM AS MOISTURE WITH THE RAW MATERIAL AND AS WATER WITH THE DIGESTING CHEMICAL AND LEAVES SAID SYSTEM WITH THE IMPREGNATED RAW MATERIAL, WHILE MAINTAINING A WATER BALANCE IN THE SYSTEM COMPRISING: MAINTAINING A POOL OF IMPREGNATION LIQUOR IN AN IMPREGNATION ZONE, CONTINUOUSLY FEEDING SAID CELLULOSIC RAW MATERIAL TO SAID POOL, INTRODUCING HEATED IMPREGNATION LIQUOR TO SAID IMPREGNATION ZONE, SAID HEATED IMPREGNATION LIQUOR BEING OF A TEMPERATURE HIGHER THAN THE TEMPERATURE OF LIQUOR IN SAID POOL, CONTROLLING THE TEMPERATURE OF SAID HEATED IMPREGNATION LIQUOR TO CAUSE A PORTION THEREOF TO FLASH AND FORM PROCESS STEAM, THE AMOUNT OF SAID HEATED IMPREGNATION LIQUOR FLASHED BEING SUCH AS TO MAINTAIN THE LEVEL IN SAID POOL SUBSTANTIALLY CONSTANT AND THEN REMOVING SAID PROCESS STEAM FROM THE SYSTEM.