From Tree Cutting to Pulping: The Impact of Tree Storage Time on Pulp Mill Economics, 2011 PEERS Conference

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Variability in wood properties represents a major impact on pulp quality and the cost associated with pulp production. Frequently, accounting data which looks at green tons of wood across the mill scales and the tons of pulp produced suggests that the pulp mill has impacted 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 the tree is brought across the scales at the mill upon accounting yield and operating cost. Percent weight loss (assumed to be changes in moisture content) were determined for Pinus taeda, Eucalyptus Dunni and Eucalyptus Grandis over a twelve week period in the winter and summer seasons. Wood samples were obtained immediately after being harvested in the forest. 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 TPD mill with a 55% pulping yield on OD fiber, the difference between using fresh cut wood verses cut trees which have been stored for 12 weeks is 1130 green tons. Assuming the mill pays $45/green ton, the change in green log usage between fresh cut and 12 week old logs can cost the mill $50850 per day.