Theory and Practice of Ozone Bleaching

Abstract

Ozone bleaching began on an industrial scale in 1992 in connection with increasing environmental pressure and customers’ demand for Elemental Chlorine Free（ECF）and Total Chlorine Free（TCF）bleached pulps. Ozone bleaching did not immediately reach its optimal efficiency from a technical viewpoint, but had to face several issues during its early years. By improving mixing technology, better understanding ozone chemistry on pulp components and tuning the whole process, ozone bleaching sequences made it possible to produce a pulp quality similar to or better than conventional ECF would do. They mark a clear milestone in the development of environmentally sound bleaching methods. Today the choice of ozone may still be motivated by ecological requirements but it is mostly justified by the economical savings resulting from chemical cost reduction. They allow combining high brightness and strength with cost efficiency. Ozone bleaching is conducted either at medium or high pulp consistency, depending on ozone bleaching process suppliers. The choice of one process over another depends on a number of factors – including investment costs, carry-over load, bleaching filtrates recirculation and bleach plant temperature profile and others.