The Impact of Log Moisture Content on Chip Size Distribution When Processing Eucalyptus Pulpwood

Abstract

Chip moisture content and especially its uniformity impact kraft pulping. However, the effect of pulp log moisture content on chip quality during chip production is not well known. Chip size distribution is important in kraft pulping as it impacts chemical use, pulp quality and recovery. This study investigated the influence of two pulp log drying periods (1 and 2 weeks) on chip moisture content and chip size distribution when chipping eucalypt pulp logs. In addition, the effect of three log classes (base, middle and top logs) on chip moisture content and chip size distribution were also analysed. Within the respective log classes, moisture content of chips produced from logs dried for 2 weeks was 5.5% to 13.2% lower than moisture content of chips produced from logs dried for 1 week. Chip moisture content also decreased with decreasing log size for both log drying periods. One week dried logs produced chips with 1.0% less over-thick chips than 2 week dried logs (1.5% versus 2.5%). One week dried logs also produced chips with 4.2% to 7.2% less accepts than chips produced from 2 week dried logs within respective log classes. Across both drying periods, over-thick chip production increased with decreasing log size, while the amount of accepts produced decreased with decreasing log size. Logs dried for 2 weeks produced chips with significantly less under-sized chips than logs dried for 1 week. Two week dried logs produced chips with 4.4% to 7.7% less pins and 0.7% to 1.0% less fines than 1 week dried logs within respective log classes. For both log drying periods, the amount of under-sized chips produced increased with decreasing log size.