Patent ID: 8197639

Claim:
A method for the continuous cooking of chemical cellulose pulp in a vapor phase digester, comprising: feeding a mixture of chips, that are to be cooked in a vapor phase digester, and a liquid to a top of the digester, the mixture fed to the digester having a liquid/wood ratio that exceeds 8:1, the mixture undergoing a dewatering process at the top of the digester in an inverted top separator, the inverted top separator feeding the mixture in an upward direction, withdrawing a first withdrawal liquid at the top separator that constitutes more than 50% of a liquid content of the mixture, feeding the chips and a remaining portion of the liquid out from the top separator to the top of the digester, establishing a pile of chips and a liquid volume inside the digester, the pile of chips being disposed above a liquid surface of the liquid volume, providing a withdrawal strainer and positioning the withdrawal strainer at a distance (a) from the liquid surface, the distance (a) being less than 0.5× of a diameter of the second withdrawal strainer, retaining the chips in the liquid volume for 0.1-15 minutes, the withdrawal strainer withdrawing a second withdrawal liquid below the liquid surface, the withdrawing of the second withdrawal liquid reducing the liquid/wood ratio at the top of the digester, and returning the second withdrawal liquid to the preceding chips treatment stage prior to the digester.