|  |
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%. |
|
| |
| |
|
