A method for estimating wood chip brightness and its applications1This article is a contribution to the series The Role of Sensors in the New Forest Products Industry and Bioeconomy.

Abstract

Methods for estimating wood chip brightness are important in classifying wood chips in chip piles, stabilizing chip brightness in the pulping process, and reducing bleaching chemical consumption in pulp mills. They also allow us to understand and control factors including outdoor storage in the summer that affect chip and pulp brightness. An accurate off-line method for estimating wood chip brightness has been developed. The method involves a two-stage grinding of air-dried wood chips to powders with small particle sizes and narrow size distributions and measurement of ISO (International Standardization Organization) brightness of the resulting powders. Using this method, ISO brightness values of 20 mill or pilot-plant thermomechanical pulps (TMP) can be linearly correlated, with an r2 value of 0.885, with ISO brightness of the mill or pilot-plant wood chips. Analyses of wood chips and TMP samples taken from a TMP mill every month for 1 year show that both the chip and TMP brightness values are the lowest in July. The method can be used for laboratory analysis of chip brightness, monitoring of chip brightness monthly variation in pulp mills, and checking the accuracy of the on-line chip brightness measurement system.