Study of On-line Measurement of Pulp Kappa Number With Spectrometry During Pulping, 2002 Technology Summit Proceedings

Wenhao Shen, Huanbin Liu, Yimin Xie

Aiming at the difficulties and problems of on-line measurement of pulp Kappa number during batch pulping, this paper proposes a new measuring idea, which is to predict the lignin content in pulp through the measurement of dissolved lignin in spent liquor with modern spectrum technology. According to the difference between the Kraft cooking and sulfite cooking, the absorption of black liquor from masson's pine in 800-900nm wave range resulted mainly from Kraft lignin, where the absorption of spent liquor from masson’s pine in 460-580nm wave range resulted mainly from lignin-sulfonate with high molecular weight, and that Kappa number maintained a linear relationship with the absorbency of the spent liquor within the wave range. Mathematical models of on-line Kappa number determination with near-infrared spectroscopy (NIRS) and visible light were developed by chemometrics for batch Kraft and sulfite cooking. After applying to sulfite pulp mill, the results showed that the new measuring method is much better than the manual method. It is successful to control sulfite pulp Kappa number and predict the end point of pulping during cooking process. The first grade ratio of pulp has been improved from 55% to 70%. The pulp Kappa number can be controlled within ±2 unit.