BCTMP filtrate recycling system and method

摘要

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.

主权项

1. A process for making bleached pulp, comprising:
(a1) pressing a first unbleached pulp mixture to produce an unbleached pulp mixture and a first filtrate; and (a2) sending at least a portion of the first filtrate to a first location (2) of a second recycled filtrate loop; (a3) contacting the unbleached pulp mixture with a first recycled filtrate obtained from a first location (3) of a first recycled filtrate loop, to obtain a first pulp mixture having a first consistency; (b) bleaching the first pulp mixture, to obtain a first bleached pulp mixture; (c) pressing the first bleached pulp mixture, to obtain a first pressed bleached pulp mixture and a second filtrate; (d) sending at least a portion of the second filtrate to a second location (5) of the first recycled filtrate loop, wherein the second location (5) is downstream of and in fluid communication with the first location (3); (e) contacting the first pressed bleached pulp mixture with a second recycled filtrate obtained from a third location (6) 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 (6) is downstream of and in fluid communication with the second location (5); (f) bleaching the second pulp mixture, to obtain a second bleached pulp mixture; (g) pressing the second bleached pulp mixture, to obtain a second pressed bleached pulp mixture and a third filtrate; (h) sending at least a portion of the third filtrate to a fourth location (8) of the first recycled filtrate loop, wherein the fourth location (8) is downstream of and in fluid communication with the third location (6); and (i) recycling at least a portion of the third filtrate in the first recycled filtrate loop to the first location (3); to obtain the bleached pulp; wherein the second recycled filtrate loop is in fluid communication with the first recycled filtrate loop to either control a fluid level in the first recycled filtrate loop, to dilute a residual bleaching agent level in the first recycled filtrate loop, or a combination thereof.