Advantages with ozone as a bleaching agent:
A powerful oxidant already at low temperature
Fast reactions, a short retention time (as a small reactor) is sufficient
Possibility of recycling filtrates to chemical recovery
Efficient delignification of all types of chemical pulps.
Ozone is produced on site through silent electrical discharge in a gas stream containing oxygen. Ozone quantities required for pulp bleaching (typically 1-10kg/Adt), are most economically produced from oxygen. The feed gas should be essentially free from water and organic compounds. Today the upper practical limit of ozone concentration is about 13%.