Practical Aspects of On-Line Chip Moisture Measurement, 1998 Pulping Conference Proceedings

Wood chip moisture content is a significant raw material variable impacting pulping conditions. Usual methods of oven drying small samples for 16 to 24 hours produces a lag-time effect that cannot be used for digester operation compensation and control. On-line continuous measurement can be used to detect chip moisture in real time, with excellent comparative accuracy to oven drying individual samples. Nuclear sources measure chip profiles and report large scale moisture content averages of chips on a moving conveyor belt, whose accuracy is greater than hand samples. Data illustrating high levels of seasonal, daily, and momentary moisture variation demonstrates the value of instantaneous measurement and reporting. Digester modeling of chips whose moisture is assumed to be constant, but whose actual daily moisture varies within normal ranges (standard deviation of 2%), shows that kappa number variation can be as high as +/- 0.78.