Economic implications of grinding, transporting and pretreating fresh versus aged forest residues for biofuel production

The moisture content in forest harvest residues is a key factor affecting the supply cost for bioenergy production. Fresh harvest residues tend to contain higher amounts of water thus making transportation inefficient. Additionally, fresh harvest residues contain greater amounts of needles and bark that may reduce the content of polysaccharides, thus, affecting the production of liquid fuels derived from cellulosic components. In this study, we estimated the downstream economic effect in the supply chain of collecting, grinding, transporting and pretreating fresh versus aged residues. Specifically, we analyzed the effect of feedstock moisture content on grinder fuel consumption, bulk density, needles and bark content and polysaccharides proportion. Fresh forest harvest residues were 60% moisture content (wet basis) and aged forest residues were 15% moisture content. The bark and needles proportion is 6.1% higher in fresh versus aged residue. Polysaccharides were 26% higher in aged residue as compared to fresh residue. On a dry tonne basis, the cost of grinding fresh residues was about the same as aged residues. However, considering the difference in bulk density on transportation cost and the difference in polysaccharides yield, the value gain for in-field drying range from USD 29.6 to 74.9 per oven-dry tonne.

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