Method for multistage bleaching using gaseous reagent in the first stage with controlled gas release

Abstract

A pulp bleaching line has an initial stage using gaseous bleaching reagent followed by its subsequent stages without intervening washing or pumping steps. The pulp is transported from the initial stage through a mixer in which the pulp is heated and/or dosed with bleaching chemicals and through the subsequent stage by retained gas pressure developed in the initial stage. A portion of the retained gas may be separated and purged from the mixer through a pressure regulating device to optimize pressure for processes which follow the mixer/heater. This permits elimination of a washer and pump normally provided between the initial reactor and subsequent bleaching stage.

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