Delimbing Hybrid Poplar Prior to Processing with a Flaiuchipper

Processing whole trees into pulp chips with chain flail delimber/debarker/chippers (DDCs) is costly. Production rates of DDCs are limited by the residence time required to remove limbs and bark. Using a pull-through delimber, we delimbed trees prior to flailing and chipping, with the objective of speeding up the latter processes. Pre-delimbing increased the productivity of the DDC by about 10 percent. The reduced cost of flail/chipping did not cover the additional cost of delimbing with the machine mix tested, but changes to equipment and operating conditions might improve the situation. In the test configuration, the delimber processed 175 trees per productive hour, about half as many as the DDC. Delimbing separated about 35 dry pounds oflimbs per tree, which may have higher value than the mixture oflimb and bark residues produced by the DDC from whole trees. Several paper companies in the Pacific Northwest are growing hybrid poplar in plantations on short rotations (less than 10 yrs) to supply some of their fiber needs. In the normal harvest sequence, these trees are mechanically felled and bunched, then forwarded to a landing with either a large front-end log loader or a grapple skidder. At the landing, the trees are delimbed and debarked with a chain flail processor, then chipped with a disc chipper (7,15). In most cases, the flail and chipper are combined into a single delimber/debarker/chipper (DDC). foliage is present. The residue takes up space in the flail's infeed and thus reduces capacity. In DDCs, the residue frequently bridges over the waste discharge chute, slowing production, reducing chip quality, and occasionally requiring that the machine be shut down and cleaned out. The large volumes of waste may also add to the following costs of operating the DDC: fuel, maintenance, and chain wear. Chain costs constitute a major part of total delimbing and debarking cost (13). Chains have been found to last as little as 12 or fewer loads, or in some cases up to 70 loads of chips (3). The waste stream from the flail is of low value; it may be utilized for fuel or compost, or if the value is too low it is piled and burned on site. Iflimbs can be separated from the bark portion of the residues, they may be suitable for a higher value use such as feedstock for the neutral sulfite semi-chemical (NSSC) pulping process that furnishes pulp for corrugated cardboard. Given the possible increase in value if the limbs can be separated, and the potential to increase flail/chipper productivity if the trees are delimbed prior to flailing, we decided to investigate alternatives to separate the activities. The possibilities included single-grip processors, irongate delimbers, and pullthrough delimbers, among others. A pull-through delimber was selected for this study because it was inexpensive and an excavator was available to feed it. Irongates are also inexpensive, but must be fed by skidders, rather than by the front-end loaders that have been Numerous studies have investigated the production rates of flails and/or the quality of the chips produced, including bark content (1,4,6,14). One of the limitations to a chain flail's productivity is the volume of residues (limbs, leaves, and bark) that must be separated from the bole wood and handled, especially during the summer months when fresh The authors are, respectively, Professor, Biological & Agricultural Engineering, Univ. of California, Davis, CA 95616; Head, Harvesting Research Group, CNR Wood Res. Inst., via Barazzuoli 23,1-50136 Florence, Italy; Fiber Farms Harvesting Manager, Boise Cascade Fiber Farm, PO Box 500, Wallula, WA 99363. This study was funded in part by the USDA Forest Servo Southern Res. Sta. under Cooperative Agreement SRS-30-CA-96-058. This paper was received for publication in July 2000. Reprint No. 9156. *Forest Products Society Member. ©Forest Products Society 2002. Forest Prod. J. 52(4):85-93. FOREST PRODUCTS JOURNAL VOL. 52, No. 4 85 Figure 1. Volvo front-end loader transporting whole trees. Figure 2. Delimbed trees being delivered to the DOC. The loader in the foreground handles the residues produced by the DOC. found to be effective for forwarding short-rotation trees (12). The objectives of this study were to: 1. Determine the productivity of a pull-through delimber when processing 6-year-old hybrid cottonwood trees; 2. Determine the effects of delimbing prior to flail debarking on: a) DDC productivity; b) Costs of delimbing, debarking and chipping; c) Chip quality; 86 d) DDC fuel usage; e) Flail chain wear; 1) Recovery of clean chips, limb material, and other residues.