Application of Near Infrared Spectroscopy to Pulp Yield and Kappa Number Estimation

Abstract

This thesis presents an investigation into near infrared (NIR) spectroscopy as a technique for determining pulp yield and kappa number for kraft pulp and black liquor samples. It is believed that proper spectra collection and preprocessing techniques combined with a linear regression analysis can produce models that accurately predict pulp yield and kappa number. Currently, no instrument exists for estimating these values simultaneously. Methods for estimating yield and kappa number consist of lengthy lab based wet chemistry techniques. NIR reflectance spectroscopy has the potential of providing a single, relatively simple instrument solution for both of these measurements. NIR transmission spectroscopy of the black liquor may provide further information and process control capability. The ability to predict yield and kappa number is a valuable process control technology for use in kraft mills.

Samples of pulp with yield and kappa number ranges typical of mills were generated from the batch kraft digestion of softwood chips and liquor of varying EA. NIR spectra of the samples were collected using little or no sample pretreatment. The idea was to analyze the samples under conditions similar to a non-idealized mill environment. Different prototype NIR spectrometers were used covering a major portion of the NIR spectrum. Correlations between the pulp yield, kappa number, NIR reflectance data of the pulp and NIR transmission data of the black liquor have been developed. These lab based calibrations were used to predict kappa number and yield values for lab generated pulp samples. The calibration models were also able to accurately predict kappa values for unknown mill pulp samples.