Fiber Recovery with Chain Flail Delimbing/Debarking and Chipping of Hybrid Poplar

Abstract This study determined how much wood was potentially available from short rotation hybrid poplar, and how much was actually recovered when trees were delimbed and debarked with chain flails and chipped. 31 groups of five trees each were measured and then processed. For trees larger than 50 kg total dry weight, potentially recoverable wood averaged 75% of total weight. Over 95% of this wood was converted into chips. Losses due to breakage by the flails, which show up in the bark discharge, amounted to 0.8 dry kg per tree and were relatively independent of tree size. Chipper reject wood losses averaged 2.3 dry kg per tree, but increased in almost direct proportion to tree size, from 1.2 kg for 50 kg trees, to 3.2 kg for 120 kg trees. For trees less than 50 kg total dry weight, potentially recoverable wood fraction was highly variable – from 50 to 75% of total weight. Because of breakage of small stems by the flail, wood recovery was also relatively low, ranging from 40 to 95%. Most of the wood loss for smaller trees showed up in the bark discharge rather than as chipper rejects. For larger trees, the chipper rejects represent the biggest opportunity for improving the recovery of wood fiber. Sharp chipper knives appear to be important for minimizing losses. Beyond that, it is not clear whether wood in the chipper rejects is the result of bole damage by the flail or chipper design characteristics.