US 6,280,568 B1Granted

Dissolved organic material control in a cellulose pulp continuous digester

AssigneeAndritz-Ahlstrom Inc.

InventorsBruno S. Marcoccia, J. Robert Prough, Richard O. Laakso, Joseph R. Phillips, Rolf C. Ryham, Jan T. Richardsen, R. Fred Chasse

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Abstract

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.

Claims7

Dependent claims

A single vessel hydraulic continuous digester assembly, comprising:

an upright continuous digester having a top and a bottom;
an inlet for a slurry of cellulosic material to be digested at the top of said digester, connected to a high pressure transfer device;
an outlet for digested pulp at the bottom of said digester;
a first cooking screen assembly located below the top of said digester;
a second cooking screen assembly located below said first cooking screen assembly;
first means for recirculating a first portion of liquid withdrawn from said first cooking screen into the interior of the digester at about the level of said first cooking screen assembly, and for extracting a second portion of the withdrawn liquid;
second means for recirculating a first portion of liquid withdrawn from said second cooking screen into the interior of the digester at about the level of said second cooking screen assembly, and for extracting a second portion of the withdrawn liquid;
means for adding a low dissolve organic material (DOM) liquid into said first portion of liquid being recirculated in each of said first and second recirculating means;
an extraction screen assembly below said second cooking screen assembly;
and
a third screen assembly located below said extraction screen assembly.

8 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/637,858Filed 15 Aug 2000 · division
Priority: 4 May 1993
Granted: 28 Aug 2001
Term ends: Not estimatedThe source records don’t support an estimate.

Classification13 codes

D21C 3/02
Pulping cellulose-containing materials: with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
D21C 3/22
Pulping cellulose-containing materials: other features of pulping processes
D21C 3/224
Other features of pulping processes: use of means other than pressure and temperature
D21C 3/24
Other features of pulping processes: continuous processes

Family

Application08/056,211Parent of this continuation-in-part · filed 4 May 1993
Application08/127,548Parent of this division · filed 28 Sep 1993
Application08/625,709Parent of this division · filed 3 Apr 1996
Application08/775,197Parent of this division · filed 30 Dec 1996
Application09/175,467Parent of this division · filed 20 Oct 1998
Application09/414,887Parent of this division · filed 8 Oct 1999
US 6,159,337 AParent of this division
US 6,086,712 AParent of this division
US 5,849,150 AParent of this division
US 5,620,562 AParent of this division
US 5,547,012 AParent of this division
Application08/127,548Parent of this continuation-in-part
US 5,489,363 AParent of this continuation-in-part
US 6,280,568 B1This patent

From the US filing history. Foreign family members aren’t listed.