Trade-offs between fuel chip quality and harvesting efficiency in energy plantations

Single-pass cut-and-chipping with modified foragers currently represents the most efficient technique for harvesting fuel chips from short rotation forestry (SRF). Modified foragers are designed to produce small chips, in the 25-30-mm length range. However, chip length settings can be adjusted for obtaining different commercial products. In that regard, it is important to determine the trade-offs of chip length manipulation, which may affect machine performance. This study tested the same modified forager designed for producing 30-mm chips, under variable chip length settings. In particular, chip length setting was adjusted both downwards to a minimum length of 5 mm (microchips), and upwards to a maximum length of 90 mm (billets). As expected, any setting adjustments that deviated from optimum values resulted in performance decline. Downward alterations of chip length setting resulted in a steady performance decline, which peaked at the shortest length setting (5 mm). Under that setting, productivity was 56% lower and diesel fuel consumption was 183% higher than under the optimum 30-mm setting. In contrast, upward alterations of chip length setting resulted in an immediate and moderate decay of machine performance at the very first increment, followed by the absence of further significant decline as additional increments were introduced. Reducing target chip length below 30 mm doubled or even quadrupled the proportion of fine particles (<3 mm) in the total chip mass, which detracted from chip quality.