From tree cutting to pulping: the impact of storage time on pulp mill economics

Abstract

Variability in wood properties has a major impact on pulp quality and the cost associated with pulp production. Frequently, accounting data for green tons of wood across the mill scales and the tons of pulp produced suggest that the pulp mill has affected the pulp yield because the tons of purchased wood divided by the tons of pulp produced changes. The current work examines the impact of the time — from when a tree is harvested in the forest to the time it is brought across the scales at the mill — on accounting yield and operating cost. Percentage weight loss (assumed to be changes in moisture content) were determined for Pinus taeda, Eucalyptus dunni, and Eucalyptus grandis over a 12-week period in the winter and summer seasons. Wood samples were obtained immediately after being harvested. The percentage weight loss within the first 5 days of storage varied from 2% to 13%, depending upon species and season, and reached 36% after 11 weeks of storage. For a 1000 tons/day mill with a 55% pulping yield on o.d. fiber, the difference between using fresh-cut wood verses cut trees that have been stored for 11 weeks is 1130 green tons. Assuming the mill pays $45/green ton, the change in green log usage between fresh-cut and 11-week-old logs can cost the mill US$50,850 per day.