ECF bleachability comparison between conventional kraft and kraft-AQ softwood pulp

The lignin content of kraft pulp entering the bleach plant can be lowered through the use of extended delignification cooking technology or through the use of oxygen delignification This work compares the bleachability of these two extended delignification processes as well as the conventional kraft process. The extended delignification technology used in this work was the Kraft-AQ process. The ECF bleach sequence employed in the comparison was DEopDD. Conventional kraft and kraft-AQ pulps studied had initial kappa numbers ranging from 15 to 30. Different overall bleach plant kappa factors were studied to determine the stoichiometry of bleaching for each of the cooking/delignification processes. The kraft-AQ cooking/delignification process gave us the best bleachability in terms of brightness, chemical requirement, and pulp viscosity.