Method for bleaching pulp with ozone with successive steps of lower

Abstract

A method for bleaching pulp with ozone and, more specifically, to a method for bleaching pulp without deterioration of pulp quality. The starting material is a medium consistency pulp with easy handling during transfer and dewatering, namely, pulp of a consistency of about 10% by weight to 20% by weight. During the initial stage of the ozone bleaching process, the reaction velocity is maintained higher, while during the latter stage of the bleaching process, cellulose attack is prevented. Specifically, pulp bleaching is done with ozone, while the pulp consistency during the bleaching process is lowered in a stepwise manner within the range for a medium consistency pulp. The decreasing of the pulp consistency in a stepwise manner during the bleaching process involves bleaching a pulp of a consistency within the range of about 10 to 20% by weight with ozone, subsequently dewatering the pulp and then diluting the pulp with water to provide a pulp consistency lower than the pulp consistency before dewatering, repeating the cycle composed of the dehydration, the diluting and the ozone bleaching steps one or more times, whereby the pulp consistency is lowered within the range of medium consistency in a stepwise manner.