Economic implications of moisture content and logging system in forest harvest residue delivery for energy production: a case study

Abstract

The need for improving the cost effectiveness of forest harvest residue utilization for bioenergy production has been widely recognized. A number of studies show that reducing residue moisture content presents advantages for transportation and energy content. However, previous research has not focused on the relative advantages of in-forest drying depending on the residue characteristics from different logging systems, comminution, and equipment mobilization. Residue drying curves were developed using finite element analysis for two primary Pacific Northwest logging systems. These curves were applied to a case study in Oregon in which mixed integer mathematical programming was used to optimize residue delivery to a hypothetical co-generation plant with a generating capacity of 6 megawatt-hours (MWh). Assuming that rear-steered trailers can access cable logging units, approximately 98% of the harvest residue generated by cable logging was delivered to the plant, compared with only 56% of residue generated with a ground-based system, mainly because collection costs incurred with ground-based system residues exceed cost benefits of drier material. By considering the energy content of drier residues, the amount of oven-dried metric tonnes (ODMT) needed to supply the plant can be reduced by 16% without affecting the energy output over a 24-month planning horizon. Lower ODMT demand and shifting to drier material decreases the overall production cost by 20.4%.