Oxygen Delignification & Bleaching
After the pulp is washed in the Brown Stock Washers, it can be bleached. There are two types of bleaching systems:
Elemental Chlorine Free (ECF) - using ClO2 and Peroxide
Total Chlorine Free (TCF) - using Oxygen and Ozone
ECF is more popular as it is less expensive. It comes with a ClO2 plant that generates ClO2 from sodium chlorate and sulfuric acid in the presence of methanol.
TCF uses oxygen and ozone. It is more expensive but it suitable for producing pulp and supporting end uses that need to be devoid of elemental chlorine.