LOW TEMPERATURE GAS PHASE CONTINUOUS DIGESTER

摘要

A cellulose pulp continuous digester (e.g.for producing kraft pulp) is operated so that it has the advantages of a hydraulic digester yet has a gas-filled zone over the liquid level. A slurry of chips and cooking liquor is introduced into the top of the digester vessel through an inverted top separator. A liquid level is established below the inverted top separator, and a chips level is established below the inverted top separator (above or below the liquid level. A gas-filled zone above the liquid level includes compressed gas, and is at a temperature of less than 160 (preferably less than 120).degree.C and at a pressure of between 50-200 (preferably 80-150) psig. The digester may have a first diameter portion (about 3-5 meters) at the top and a second diameter portion (at least about seven meters) below the top, with the inverted separator in the first diameter portion, th e liquid level in the first diameter portion, and the chips level in the secon d diameter portion. A shoulder is provided between the first and second diameter portions and a withdrawal screen is preferably mounted just below the shoulder in the second diameter portion. A plurality of different liquor flows may be extracted from the inverted top separator.