METHOD FOR DIGESTING WOOD CHIP BY ALTERNATELY CHANGING CHIPS HAVING DIFFERENT KAPPA NUMBERS IN THE SAME DIGESTER

摘要

PURPOSE: To rapidly change pulp to a desired Kappa number level in change of pulp of different kinds by changing an amount of digested liquid fed to a digester and a digestion temperature at a specific time. ;CONSTITUTION: A mixture of chips and a digestion liquid is introduced to the top of a digester 8 and the mixture and a necessary amount of an alkali are supplied through conduits 17, 19 and 20 to a transfer recycle return liquid. An active alkali is maintained in a range of 15-20% calculated as Na₂O per weight of absolute dry weight wood chip. When an alkali addition ratio is varied from a high value to a low value, the amount of alkali solution is increased 30-90 minutes before chips reach a digestion-based inlet and an inlet temperature of digestion zone is maintained 1-5°C higher than a desired temperature for 60-180 minutes. In the opposite case, the amount of the alkali solution is reduced to a desired level amount simultaneously with the arrival of the wood chips to the digestion-based inlet and an inlet temperature of the digestion zone is maintained at 1-4°C lower than a desired temperature for 30-90 minutes.;COPYRIGHT: (C)1993,JPO&Japio