International Paper Company

Caifang F Yin

Jasper H Field

Kent Witherspoon

Christopher P Hung

Hugh P Gallagher

Jianhua Wang

A process for making bleached pulp comprises contacting an unbleached pulp mixture with a first recycled filtrate obtained from a first location () of a first recycled filtrate loop, to obtain a first pulp mixture having a first consistency; bleaching the first pulp mixture, to obtain a first bleached pulp mixture; pressing or dewatering the first bleached pulp mixture, to obtain a first pressed bleached pulp mixture and a second filtrate; sending at least a portion of the second filtrate to a second location () of the first recycled filtrate loop, wherein the second location () is downstream of and in fluid communication with the first location (); contacting the first pressed bleached pulp mixture with a second recycled filtrate obtained from a third location () of the first recycled filtrate loop, to obtain a second pulp mixture having a second consistency, wherein the second consistency is greater than the first consistency, and wherein the third location () is downstream of and in fluid communication with the second location (); bleaching the second pulp mixture, to obtain a second bleached pulp mixture; pressing or dewatering the second bleached pulp mixture, to obtain a second pressed bleached pulp mixture and a third filtrate; sending at least a portion of the third filtrate to a fourth location () of the first recycled filtrate loop, wherein the fourth location () is downstream of and in fluid communication with the third location (); and recycling at least a portion of the third filtrate in the first recycled filtrate loop to the first location (); to obtain the bleached pulp.

BCTMP filtrate recycling system and method

A process for making bleached pulp comprises contacting an unbleached pulp mixture with a first recycled filtrate obtained from a first location of a first recycled filtrate loop, to obtain a first pulp mixture having a first consistency; bleaching the pulp mixture, to obtain a first bleached pulp mixture; pressing or dewatering the bleached pulp mixture, to obtain a first pressed bleached pulp mixture and a second filtrate; sending a portion of the second filtrate to a second location of the first recycled filtrate loop, wherein the second location is downstream of and in fluid communication with the first location; contacting the pressed bleached pulp mixture with a second recycled filtrate obtained from a third location of the first recycled filtrate loop, to obtain a second pulp mixture having a second consistency, wherein the second consistency is greater than the first consistency, and wherein the third location is downstream of and in fluid communication with the second location; bleaching the second pulp mixture, to obtain a second bleached pulp mixture; pressing or dewatering the second bleached pulp mixture, to obtain a second pressed bleached pulp mixture and a third filtrate; sending a portion of the third filtrate to a fourth location of the first recycled filtrate loop, wherein the fourth location is downstream of and in fluid communication with the third location; and recycling a portion of the third filtrate in the first recycled filtrate loop to the first location.

This invention relates to an improved bleaching process for bleaching pulp comprising at least one bleaching stage which comprises treating a hardwood pulp with a bleaching agent comprising ClOin the presence of a weak base such as, for example, Mg(OH)preferably at pH from about 3.5 to about 6.5. The invention is also relates a bleaching process for bleaching pulp having two or more bleaching stages, at least one of which and preferably two of which comprises treating a hardwood pulp with a bleaching agent comprising ClOin the presence of a weak base such as, for example, Mg(OH)preferably at pH from about 3.5 to about 6.5.

Process of bleaching hardwood pulps in a D1 or D2 stage in a presence of a weak base

This invention relates to an improved bleaching process for bleaching pulp comprising at least one bleaching stage which comprises treating a softwood pulp with a bleaching agent comprising ClOin the presence of a weak base such as, for example, Mg(OH)preferably at pH from about 3.5 to about 6.5. The invention is also relates a bleaching process for bleaching pulp having two or more bleaching stages, at least one of which and preferably two of which comprises treating a softwood pulp with a bleaching agent comprising ClOin the presence of a weak base such as, for example, Mg(OH)preferably at pH from about 3.5 to about 6.5.

Process of bleaching softwood pulps in a D1 or D2 stage in a presence of a weak base

The specification discloses an improved bleaching sequence which provides significant reduction in filtrate volumes and amounts of absorbable organic halide (AOX), color, and chemical oxygen demand (COD) in the effluent. These reductions are achieved without adversely affecting the brightness and viscosity properties of the bleached pulp and without a high capital cost and operating cost penalty or impact on existing mill processes. The bleaching sequence according to the invention for reducing filtrate volumes is an E D E D or E D E D bleaching sequence wherein substantially all of the filtrates from the later bleaching stages are recycled to earlier bleaching stages and eventually treated in the initial E or E stage prior to discharge from the plant. An advantage of the invention is that pulp having a Kappa number of greater than about 25 for softwood and greater than about 15 for hardwood may be fed to the bleaching process while still providing a bleached pulp having sufficient brightness, viscosity characteristics and good pulp yield.

Elemental-chlorine-free bleaching process having an initial Eo or Eop stage

The invention is directed to a method for treating an aqueous waste material in order to reduce the volume of the material for disposal and/or landfill. In the method, an aqueous waste material containing organic compounds is contacted with calcium carbide under conditions which cause water and calcium carbide to react to produce acetylene and a residue. The acetylene is burned in the presence of the residue to further reduce the volume of material for disposal.

Method for treatment of an aqueous waste material

The invention described in the specification relates to a process and apparatus for reducing AOX, COD and color bodies from the filtrate streams generated by a kraft pulp bleaching sequence. The method involves vigorously mixing an F.sub.D filtrate with an F.sub.E filtrate to form a filtrate mixture and treating the filtrate mixture with a coagulating compound, a flocculating compound and recycled foam concentrate. After chemically treating the filtrate mixture, the mixture is foamed with air in order to capture floc which formed in the mixture. Concentration of the foam and recycle of the foam to the filtrate mixture has been found to significantly increase the concentration of and reduce the amount of solids generated in the treatment system.

Foam separation method for reducing AOX, COD, and color bodies of kraft

The invention described in the specification relates to a process and apparatus for the reduction of adsorbable organic halide (AOX), chemical oxygen demand (COD) and color bodies from the filtrates generated in a chlorine compound-containing pulp bleaching sequence. The method involves vigorously and intensely mixing certain pulp bleaching filtrates in order to lower the AOX content of the filtrate and the use of a peroxy compound and a ferrous salt catalyst to treat a combined filtrate streams thereby significantly reducing the level of AOX, COD and color in the effluent leaving the pulp bleaching plant.

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Mason, OH, United States of America

Caifang F Yin