Sulfide Profiling for Increased Kraft Pulping Selectivity, 1996 Pulping Conference Proceedings

Jian Er Jiang

Ahlstrom Machinery

Don. W. Herschmiller

H. A. Simons Ltd.

At about 13-14 kappa number, addition of all available sulfide to the beginning of a cook was found to increase the brownstock pulp yield by about l% on wood, and pulp viscosity by 20% Pulping rate and pulp strength properties were also improved by sulfide profiling. It can be concluded that the beneficial effects of sulfide profiling on pulping selectivity and on brownstock strength are more pronounced in the lower kappa range. The improved pulping selectivity makes it possible to extend modified kraft cooking from about 18 kappa number to about 13 kappa number, without any noticeable loss in pulp yield and strength properties. Keywords: Kraft pulping, sulfide, profile, selectivity, modified cooking, extended delignification

Results from kinetics studies suggest that the effect of hydrosulfide concentration on pulping varies in the three phases of kraft delignification [l-6]. The fast initial phase shows an apparent zero-order reaction kinetics with respect to hydrosulfide concentration, provided the sulfidity is above a certain minimum. In the bulk phase, an apparent reaction order of approximately 0.4 can be assigned [1,2,4]. A high concentration of hydrosulfide ions near the transition from the initial to the bulk phase also improves pulping selectivity [6-8]. In the slow residual phase, delignification is independent of the sulfide concentration [1,2,4]....