Transpirational Drying Effects on Energy and Ash Content from Whole-tree Chipping Operations in a Southern Pine Plantation

Newly announced North American bioenergy projects will likely increase the demand for woody biomass substantially over the next five to ten years. High harvesting and transportation costs for woody biomass from forests are commonly identified as key constraints to expanding this new industry and meeting expected wood fiber demand. In addition to a cost-competitive feedstock, wood energy facilities prefer drier raw material to maximize energy content and cleaner material with less dirt or grit to minimize the ash remaining after combustion. We examined extended transpirational drying times of felled trees to study their correlation with moisture, ash, and energy content. We compared production rates and material properties for three drying treatments of felled trees in a 14-year old planted loblolly pine stand: (1) drying in the field for approximately eight weeks, (2) drying in the field for approximately four weeks, and (3) freshly felled (or green) trees. A range of operational variables including fuel consumption, knife wear, chipper productivity, the number of stems per linear foot of trailer, and tons per linear foot of trailer were also compared. INTRODUCTION Higher market prices for fossil fuels as well as proposed policy changes to support renewable energy and reduce carbon emissions have recently led to a large number of bioenergy projects being announced which will consume woody biomass. Projects announced for North America as of September 2009 will substantially increase wood energy capacity and will potentially consume more than 60 million green tons of wood biomass feedstock (RISI 2009). A survey of top state forestry officials recently identified high harvesting and transportation costs for woody biomass from forests as the top constraint to expanding this potential new industry (Aguilar and Garrett 2009).