Advances in high tonnage supply systems for southern pine biomass

In this study, a high-tonnage harvesting system designed specifically for southern pine bioenergy stands was built, deployed, and evaluated in a production setting.  The system consists of a new track-type feller buncher, high-capacity wheeled skidder, in-woods chipper, and high-capacity chip trailers for trucking transpirationally-dried wood.  The Tigercat 845D feller buncher used a prototype shear felling head and incorporated several options to maximize small-stem productivity. In plantations and natural stands, the feller buncher produced approximately 100 green tons of biomass per productive machine hour (gt/PMH) and 120 gt/PMH, respectively. The ability of the feller buncher to maintain high productivity in stands with smaller diameter stems is something not achieved in previous feller buncher designs.  The feller buncher was paired with a single Tigercat 630D skidder and high-capacity grapple; with measured productivity up to 143 gt/PMH. Transpirational drying of woody biomass was tested at multiple locations.  Drying times of 72 days in late summer resulted in mean wood moisture content of 26% for skidder bunches and 39% for large piles at roadside as compared to moisture contents of 55% to 58% for freshly cut trees.  The project demonstrated achievement of maximum legal payloads on high-capacity chip trailers with transpirationally-dried wood. Transportation costs of chips (for 50-mile haul at $4 per mile) were reduced by as much as $5 per dry ton for wood dried to 35% MC. The entire procurement system must be optimized to take full advantage of productivity gains achieved with machines and transpirational drying techniques developed in this project.