ADVANCED ATLINE KAPPA MEASUREMENTS WITH NIR- SPECTROSCOPY FOR FIBRELINE OPTIMIZATION

摘要

With increasing worldwide competition, pulp and paper manufacturers require greater emphasis on cost reduction, increased product efficiency and quality, while minimizing environmental impact. Although the chemical recovery process plays a critical role in the economic viability of pulp mills, efficient operation of the digester is equally important to ensure excellent yield and product quality. The kappa number of pulp, or residual lignin content, estimates the extent of delignification in the cooking process and is a critical parameter for digester and bleaching processes. To optimize cooking yield and product quality, kappa number is used as a feedback parameter to automated control algorithms, allowing for adjustments to the liquor charge and time-temperature profile of the digester, as well as the bleaching chemical charge in the bleach plant. Kappa measurement has become even more critical due to greater variability in chip quality (i.e., moisture content, size distribution, and species mixtures) necessitating varying cooking conditions; thus greater demand on more frequent kappa measurements. Although many online analyzers exist for kappa measurement, at-line measurement is still required as cross-checks. Results from the application of the advanced spectroscopic technique indicate that kappa accuracy from operator-to-operator and from lab-to-lab is within ≤ 1 kappa unit. The calibration and validation results from various mill installations illustrate that residual lignin measurement using NIR spectroscopy, as per described technique, is linear from 5 kappa to 120 kappa, and is independent of wood species. Correlation coefficient (R~2) of 0.98 is obtained for wet pulp and accuracy within 0.7 kappa unit. For unbleached finished pulp sheets, accuracy is within ±0.5 kappa unit and correlation coefficient of 0.99 (R2). This paper will present the results obtained from the mill implementation and will also briefly discuss the improvements in digester operations resulting from better kappa determination, along with savings from reduced process variability. Applications in product segregation will also be discussed.