Ahlstrom Machinery, Inc.

Kamyr, Inc.

Andritz-Ahlstrom Inc.

Andritz Inc.

Richard O Laakso

J Robert Prough

Bruno S Marcoccia

R Fred Chasse

Joseph R Phillips

C Bertil Stromberg

Rolf C Ryham

Jan T Richardsen

Kaj Henricson

Carl L Luhrmann

Keith Vogel

John F Bolles

Auvo K Kettunen

Michael D Meredith

Patrick J Sullivan

Jay J Miele

Jen T Richardsen

A method is disclosed for extracting liquor from a cellulose slurry for a continuous digester comprising the steps of: providing the cellulose slurry of liquor and chips of cellulose fiber material to a separator; extracting a first stream of liquor from the separator; extracting a second stream of liquor from the separator, where the second stream has an effective alkali (EA) concentration greater than the EA concentration of the first steam; outputting the first stream from the separator and outputting the second stream from the separator separately from the second stream, and outputting a condensed slurry from the separator to a digester vessel.

Continuous digester having a sectioned top separator with multiple liquor extraction ports

In the feeding of a slurry of comminuted cellulosic fibrous material to a digester (continuous or batch) in the production of chemical pulp, one of the tanks used in the feed system (which preferably includes a high pressure feeder) may be eliminated without consequent loss of its function by providing a single tank with the combined functions of controlling the level of liquid in a slurrying conduit which supplies slurry to a slurry pump, and storing and substantially continuously supplying liquid to a make-up liquid pump connected to the digester. The single tank preferably surrounds the slurrying conduit and is substantially concentric, and in liquid communication, with it. A gap of 3-48 inches may be provided between the bottom of the conduit and a connection to the slurry pump. A screen or strainer may be provided in the gap, which is substantially surrounded by the tank. The return system from the low pressure outlet of the high pressure feeder to the slurrying device (like the conduit and tank surrounding it, or a conventional clip tube) may be devoid of one or more of an in-line drainer, level tank, centrifugal separator, and surge tank.

Chip feeding to a comminuted cellulosic fibrous material treatment vessel

Kraft pulp of increased strength and bleachability may be produced with decreased consumption of effective alkali, and at a lower H factor, by keeping the dissolved organic material (DOM) concentration low substantially through the entire kraft cook, including by extracting high DOM liquid from at least one part of a continuous digester and replacing it with much lower level DOM liquid. Existing pulp mills having two-vessel hydraulic, one-vessel hydraulic, or other systems may be retrofit to provide for extractions and additions of low DOM dilution liquor (including substantially DOM-free white liquor). Also, commercial size batch digesters (8 tons per day of pulp or more) can be operated with low DOM liquor to produce increased strength pulp. Using dilution with low DOM liquor also results in reduced H factor and effective alkali consumption, and increased bleachability.

Dissolved solids control in pulp production

Dissolved organic material control in a cellulose pulp continuous digester

A cellulose pulp continuous digester (e.g. for producing kraft pulp) is operated so that it has an inverted top separator and is hydraulically filled to above the level of the inverted top separator, and may be substantially completely hydraulically full. A plurality of different liquor flows may be extracted from the inverted top separator, and an in-line drainer may be provided in a conduit through which liquid is extracted.

Continuous digester with inverted top separator

Kraft pulp of increased strength and bleachability may be produced with decreased consumption of effective alkali, and at a lower H factor, by keeping the dissolved organic material (DOM) concentration low substantially through the entire kraft cook, including by extracting high DOM liquid from at least one part of a continuous digester and replacing it wit much lower level DOM liquid. Existing pulp mills having two-vessel hydraulic, one-vessel hydraulic, or other systems may be retrofit to provide for extractions and additions of low DOM dilution liquor (including substantially DOM-free white liquor). Also, commercial size batch digesters (8 tons per day of pulp or more) can be operated with low DOM liquor to produce increased strength pulp. Using dilution with low DOM liquor also results in reduced H factor and effective alkali consumption, and increased bleachability.

Dissolved organic materials control in cellulose pulp production

A method of controlling the pressure of a vertical continuous comminuted cellulosic fibrous material (wood chip) digester is provided using a pressure-control extraction in a zone relatively insensitive to changes in the flow rate of liquid introduction or removal. The method comprises controlling the pressure in the digester primarily (or substantially exclusively) by varying the flow rate of liquor extracted from the pressure-control extraction to maintain the pressure in the digester at a desired superatmospheric level while avoiding non-uniform, unstable material movement in the counter-current washing zone; and introducing dilution liquid into the digester at the at least one recirculation-dilution loop. The pressure-control extraction is preferably substantially the upper extraction in the digester. Substantially except during excessive over pressure and under pressure conditions the extraction flow from the main extraction is maintained substantially constant. Substantially only during excessive over pressure and under pressure conditions pressure control may also be practiced by controlling the rate of dilution into the at least one recirculation-dilution loop, and the extraction from the main extraction.

Method of controlling pulp digester pressure via liquor extraction

DOM control in cellulose pulp production

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, the liquid level in the first diameter portion, and the chips level in the second 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.

Low temperature gas phase continuous digester

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 chips are heated by recirculating and heating liquid using a recirculation loop below the chips level, and a countercurrent flow zone is preferably provided.

Continuous digester with a low temperature gas-phase

Digester systems for producing paper pulp from comminuted cellulosic fibrous material take into account the level of dissolved organic materials (DOM), such as lignin, hemi-cellulose, and cellulose, maintaining the DOM level at about 100 g/l throughout the cook (particularly kraft cook). In order to make sure there is sufficient liquid to slurry the material in the feed system of a two vessel system, some liquid is withdrawn from the circulation conduits between the digester and impregnation vessel, cooled, and fed to the feed system. In a vapor phase digester, the level of liquid at the top of the digester is more precisely controlled by circulating some of the withdrawn liquid from a circulatory loop of the digester to the level tank associated with the feed system. An in-line drainer may be provided in the feed system between a make-up liquor pump and a liquid inlet conduit leading to the top of an impregnation vessel. Within the digester, a set of extraction/dilution screens is provided specifically positioned and spaced from each other, and with respect to a reintroduction conduit opening, so that mixing of different DOM concentration liquids is minimized.

Continuous digester having means for implementing low dissolved solids

Low dissolved solids control in pulp production

The sulfide ion concentration and sulfidity of kraft cooking liquor during kraft cooking of cellulose pulp is selectively increased. After treatment in a first treatment zone in which impregnation or kraft cooking takes place using a kraft cooking liquor having a first sulfide ion concentration and sulfidity, black liquor is extracted from the material, liquid is withdrawn from the material and dilution liquid is added to the withdrawn liquid and the withdrawn liquid with dilution liquid is reintroduced. In a second treatment zone after the first zone a second kraft cooking liquor is introduced having a second sulfide ion concentration and sulfidity greater than the first sulfide ion concentration and sulfidity (typically by about 20-50%), including by manipulating controlling the flow rate of extraction and the flow rates of withdrawal of liquid and addition of dilution liquid. The pressure of the continuous digester is controlled in a unique manner that avoids disruptions to the column of pulp continuously moving downwardly in the digester, anywhere in the digester, but particularly avoids non-uniform, unstable material in the countercurrent washing zone. The pressure is controlled by withdrawing liquid from, and introducing liquor into, the digester at at least one additional extraction-dilution loop aside from the main extraction of the digester and the wash dilution liquid introduction mechanism below the wash screens. Pressure can also be maintained (e.g. at about 130-170 psi) by also controlling the amount of wash dilution liquor, and by varying the extraction flow.

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Queensbury, NY, United States of America

Richard O Laakso