Process for manufacturing bleached pulp including recycling
AssigneeChampion International Corporation
InventorsGerald E. Maples, Joseph R. Caron, John A. Fleck
Life of this patent
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Abstract
A process for bleaching wood pulp is provided comprising subjecting the wood pulp, after brown stock washing, to an oxygen delignification stage, a washing sequence, a first chlorine dioxide bleaching stage, an oxidative extraction stage, optionally at least one final chlorine dioxide bleaching stage and then recycling the filtrate from the oxidative extraction stage counter-currently through the bleaching plant and brown stock washing. Additionally, and quite beneficially, the filtrate from the first chlorine dioxide bleaching stage is also recycled counter-currently through the brown stock washing thereby significantly reducing the environmental impact associated with the manufacture of bleach wood pulp.
Claims52
A process for manufacturing bleached wood comprising subjecting wood pulp having a Kappa Number equal to or less than about 30 after at least one brown stock washing stage to the following steps:
- a first acidic bleaching stage wherein the pH at some point during said bleaching stage is less than 7;
- and
- an oxidative alkaline extraction stage wherein the pH at some point during said extraction stage is greater than 7;
- and said process further comprising:
- subjecting said pulp to an acid wash wherein the pH at some point during said acid wash is less than 7, prior to said first acidic bleaching stage to remove all or a portion of non-process metals contained in said pulp;
- recycling countercurrently all or a portion of the filtrate from said first acidic bleaching stage and all or a portion of the filtrate from said oxidative alkaline extraction stage as wash water to said at least one brownstock washing stage and to a weak black liquor to form a weak black liquor which comprises said recycled filtrates;
- recycling said weak black liquor to a black liquor evaporation stage to produce a strong black liquor which comprises chloride and/or potassium salts and sulfur containing compounds;
- combusting said strong black liquor to produce a smelt stream and a flue gas comprising particulates which comprise chloride and/or potassium salts and sulfur containing compounds and separating said smelt stream and said flue gas;
- treating said flue gas to separate said particulates as ash, and treating said ash to form a component relatively low in chloride and/or potassium salts and relatively rich in sulfur containing compounds and a component comprising chloride and/or potassium salts;
- and
- recycling said component relatively low in chloride and/or potassium salts and relatively rich in sulfur containing compounds to the strong black liquor and discharging said component comprising chloride and/or potassium salts;
- and
- recycling said smelt to a causticizing system to regenerate pulping liquor.
A process for bleaching wood pulp comprising subjecting the wood pulp after brown stock washing to the following steps:
- a first acidic bleaching stage wherein the pH at some point during said bleaching stage is less than 7;
- and
- an oxidative alkaline extraction stage wherein the pH at some point during said bleaching stage is greater than 7 and said process further comprising:
- treating all or a portion of filtrate from said first acidic bleaching stage to remove from said filtrate all or a portion of non-process metals contained in said pulp to form treated filtrate;
- recycling countercurrently all or a portion of said treated filtrate from said first acidic bleaching stage and all or a portion of filtrate from said oxidative alkaline extraction stage as wash water to said at least one brownstock washing stage to a weak black liquor forming a weak black liquor which comprises said recycled filtrates;
- recycling said weak black liquor to a black liquor evaporation stage to produce a strong black liquor which comprises chloride and/or potassium salts and sulfur containing compounds;
- combusting said strong black liquor to produce a smelt stream and a flue gas comprising particulates which comprise chloride and/or potassium salts and sulfur containing compounds and separating said smelt stream and said flue gas;
- treating said flue gas to separate said particulars as ash and treating said ash to form a component comprising chloride and/or potassium salts and a component relatively low in chloride and/or potassium salts and relatively rich in sulfur containing compounds;
- and
- recycling said component relatively low in chloride and/or potassium salts and relatively rich in sulfur containing compounds to said strong black liquor and discharging said component comprising chloride and/or potassium salts;
- and
- recycling said smelt to a causticizing system to regenerate pulping liquor.
Dependencies are inferred from the claim text.