Patent ID: 8753477

Claim:
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.