Ozone (O3) bleaching is a relatively new bleaching chemical that was studied in pilot scale in
several countries in the 1980s and introduced in pulp mills in the beginning on the 1990s. The
most well known installation is the Lenzing sulfite mill in Austria that started an ozone pilot
plant of 100 t/d in 1990. In 1992 the Franklin mill in the USA and the Mönsterås mill in Sweden
were the first kraft mills to include this bleaching stage on full mill scale. Today about 20 mills
in the world use ozone bleaching in their sequences. One of its merits is that softwood kraft pulp
of full brightness can be obtained with ozone together with oxygen and hydrogen peroxide stages
without the use of any chlorine containing chemicals. Ozone based totally chlorine free
bleaching is possible to use also for production of strong fully bleached softwood kraft pulps.
Ozone has also become interesting in combination with chlorine dioxide stages as a way to reduce
the demand of chlorine dioxide in ECF-sequences.
During the 1980s and 1990s the environmental concern