Ozone Delignification/Bleaching

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 was introduced as a bleaching chemical on industrial scale in the beginning of the 1990s. The primary driving force was to achieve full pulp brightness without using of chlorine containing chemicals. Today ozone is used in both TCF and ECF bleaching. Since ozone is a powerful bleaching agent it means reduced consumption of other bleaching chemicals.

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%.