On the Relationship Between Pulping Temperature and Kraft Pulp Kappa Uniformity at the Single Fiber Level, 2005 Engineering, Pulping & Environmental Conference

Temperature is one of the pulping variables that affects pulp kappa uniformity. Previous research has shown indirectly that higher pulping temperatures result in non-uniform pulp. The single fiber kappa analyzer (FKA) provides a means to directly measure pulp kappa uniformity and to investigate the relationships between digester operating conditions and that uniformity. In this study, 68 softwood pulp samples, cooked in 16 different trials in a commercial displacement batch digester, are analyzed with the FKA. These pulps are cooked at either 168º C or 176º C, while keeping target kappa near 20 by changing cooking time. A single fiber kappa distribution is obtained for each pulp sample. The coefficient of variation (COV) of the fiber kappa population distribution is used as a metric for pulp uniformity. In the study, the relationship between the kappa distribution COV and the pulping variables - cooking temperature, time-to-constant-temperature, and chip thickness distribution - is studied statistically by multiple linear regression analysis. Results of the analysis show that higher temperature and rapid time-to-temperature produce pulps that are more non-uniform. A negative effect of chip thickness on pulp uniformity was also observed although it was less significant as the chip thickness distributions in the trial cooks were relatively consistent.