Rapid D/Z and Z/D Stages for Delignification of Southern Pine Kraft Pulp, 2002 International Pulp Bleaching Conference Proceedings

Charles E. Courchene, Thomas J. McDonough, Mark K. Turner

Partial replacement of chlorine dioxide with ozone in an initial delignification stage can provide bleach cost savings, extend ClO2 generator capacity, and reduce the generation of bleach plant filtrate AOX and color. In addition, capital savings can be realized with the use of short retention times for both the D and Z stages. The purpose of the work described in this paper was to develop data for (D/Z) and (Z/D) delignification of southern pine in a way that takes advantage of the rapid reaction rates of both chlorine dioxide and ozone. A series of laboratory experiments were done with (D/Z)E and (Z/D)E delignification stages in a two-level factorial to determine the effects of retention times, order of chemical addition, total kappa factor, temperature, consistency, carry-over, and level of ozone substitution on the extent of delignification of a southern pine kraft pulp. Only kappa factor, temperature, presence of carry-over, and level of ozone substitution were found to be significant factors. Rapid D and Z stages (0.5-1 min) were as effective as longer retention time stages. Additional experiments were done to compare (D/Z)(EPO) and (Z/D)(EPO) stages to D(EPO) for determining the optimum level of ozone addition.