An evaluation of existing and conceptual short-rotation energy plantation harvesting machines and systems

The literature was reviewed to determine the probable characteristics of short-rotation energy plantations. The influences these plantation characteristics would have on harvesting machine and system design were evaluated. Significant plantation and system characteristics affecting the harvesting of energy biomass include species, spacing, rotation, generation, row and road layout, plantation size, soil type, terrain, and end-product form.

A prototype short-rotation energy plantation harvester attachment for a medium-size farm tractor or skidder was described and is under construction. Tests were performed on two types of circular saws as severance devices. The tests concluded that circular carbide-tipped peg-tooth saws were an efficient method of cutting the stems, requiring only about 9 net horsepower and leaving very cleanly-cut stump surfaces.

The prototype harvester system and three other large existing or conceptual biomass harvesters were simulated on a 100 acre short-rotation energy plantation under three spacing and three rotation assumptions. Simulation results showed that wider (4' x 4' to 8' x 8’) spacings gave slightly lower harvesting costs and better productivities than 2' x 2' spacings. Rotations or generations with more volume per stem generally resulted in lower harvesting costs. The VPI short-rotation harvesting attachment system had harvesting costs and productivities comparable to the large, single-purpose machines (SIKOB harvester, Koch-Nicholson Mobile Chipper, and the Georgia-Pacific Biomass Harvester). The most favorable harvesting costs were about $10 per dry ton of chips; the most favorable system productivities were about 7 to 10 dry tons per hour.