Kamyr, Inc.

Ahlstrom Machinery, Inc.

Andritz-ahlstrom Inc.

Carl L Luhrmann

J Robert Prough

Bruno S Marcoccia

Richard O Laakso

C Bertil Stromberg

Jan T Richardsen

Mark D Barrett

Victor L Bilodeau

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

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liquor having a first sulfide ion concentration and sulfidity, black liquor is extracted from the material, liquid is withdrawn from the material and dilution liquid is added to the withdrawn liquid and the withdrawn liquid with dilution liquid is reintroduced.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.

Method of controlling the pressure of a continuous digester using an

Method for selectively increasing the sulfide ion concentration and

In the production of cellulose pulp (e.g. kraft pulp) utilizing a continuous digester having a number of different feed points for cooking (e.g. white) liquor and utilizing a high pressure feeder, the volume of cool white liquor that is applied to the feed system is reduced compared to conventional processing. This can cause excessive hammering, and damage the high pressure feeder and adjacent piping and equipment. In order to avoid this, liquid being recirculated from the top of the digester back to the high pressure feeder is cooled by passing it into a heat exchanger into heat exchange relationship with a cooler liquid, with the flow of coolant automatically controlled by sensing the temperature of the recirculated liquid. The temperature in the feed system can further be lowered by cooling the cooking liquor before it is added to the pulp slurry, as by passing it to a flash tank so that its temperature is reduced at least 10.degree. C., and the flashed steam can be used in an evaporator.

Top circulation line cooling for a modified cook digester

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Glens Falls, NY, United States of America

Carl L Luhrmann