Abstract: A process control method for adjusting chemical application in response to the pulp brightness and/or lignin content is realized by utilizing a coupled control feedforward, feedback or combination feedforward/feedback control system, wherein brightness measurements are made between successive lignin content measurements and adjustments made to the chemical application in response to a comparison value.

Abstract: The use of hot water extraction (pH 7-8, 165.degree. F.) in place of an alkaline extraction in pulp bleaching sequences between an ozone delignification stage alkaline wash and a brightening stage allows higher strength pulp to be achieved at essentially the same brightness levels using reduced overall amounts of bleaching chemicals. In addition, effluents from pulp washing stages following these treatments can be recycled without generating scale in process equipment because the solubility of salts that could form such scale is significantly greater in these effluents.

Abstract: A method for reducing or eliminating the formation of salt scale upon process equipment caused by precipitation of insoluble salts during the bleaching of pulp. The pulp is subjected to a bleaching sequence which includes a plurality of pulp treatment steps, wherein at least one pulp treatment step is conducted under alkaline conditions and at least one pulp treatment step is conducted under acidic conditions. A filtrate stream which contains dissolved insoluble salts therein is thus generated, and at least a portion of the filtrate stream is combined with an alkaline stream and pulp to cause the salts to associate with the pulp, thus removing the salts from the filtrate stream to reduce or eliminate the formation of salt scale upon process equipment during the bleaching of the pulp.

Abstract: A process control for adjusting bleaching agent application in response to the pulp brightness and/or K number is realized by utilizing a coupled control feedforward and/or feedback control system or combination thereof wherein brightness measurements are made between successive K number measurements and adjustments made to the bleaching agent application in response to a comparison value.

Abstract: A method for reducing or eliminating the formation of salt scale upon process equipment caused by precipitation of salts during the bleaching of pulp. The pulp is subjected to a bleaching sequence which includes a plurality of pulp treatment steps, wherein at least one pulp treatment step is conducted under alkaline conditions and at least one pulp treatment step is conducted under acidic conditions. A filtrate stream which contains dissolved salts therein is thus generated, and at least a portion of the filtrate stream is combined with an alkaline stream and pulp to cause the salts to associate with the pulp, thus removing the salts from the filtrate stream to reduce or eliminate the formation of salt scale upon process equipment during the bleaching of the pulp.