Study of on-line pulp Kappa number determination with spectrometry during batch pulping

摘要

Aiming at the difficulties and problems of on-line measurement of pulp Kappa number during batch pulping, this paper proposed a new measuring idea, which was to predict the lignin content in pulp through the measurement of dissolved lignin in cooking liquor with modern spectrum technology. According to the difference between the sulfite cooking and Kraft cooking, it was discovered that the absorption of red liquor from masson's pine in 460-580 nm wave range resulted mainly from lignin-sulfonate with high molecular weight, where the absorption of black liquor from masson's pine in 800-900 nm wave range resulted mainly from Kraft lignin, and Kappa number maintained a linear relationship with the absorbency of the cooking liquor within the wave range. Mathematical models of on-line Kappa number determination with visible spectroscopy and near-infrared spectroscopy (NIRS) were developed by chemometrics for batch sulfite and Kraft cooking. After applying to sulfite pulp mill, the results showed that the new measuring method was much better than manual method. It was obviously that with this new method 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 could be controlled within +-2 unit.