Application of air classification, acid leaching and formulation to manage feedstock cost, quality and quantity for bioenergy

Biomass has significant potential to be used for production of fuels, chemicals and energy. However, in a given location, biomass availability, cost and quality can vary markedly. Strategies to manage these variables must be identified and implemented so that consistent low-cost and high-quality feedstocks can be delivered to biorefineries year round. In this study, we examine air classification combined with acid leaching as methods to mitigate high ash and to increase feedstock supply through the use of logging residues.  Air classification separated residues into light fractions which contained concentrated amounts of introduced soil ash; and depleted heavy fractions with relatively lower total ash content.  Acid leaching was applied to the light fractions and found to remove both soil contaminants and physiological ash.  Assuming a nine county supply region in South Carolina, formulation techniques were then used to develop blends of air classified and leached logging residues with pulpwood that met ash quality specifications (0.9% total ash and 1200 ppm alkali and alkaline earth metals) at the lowest possible cost for pyrolysis applications.  The lowest cost blend met both of the ash quality specifications and consisted of 12.5% pulpwood, 14.5% untreated logging residues and 73.0% air classified and leached logging residues at a cost of $92.88/ton.  This is a 20% reduction in feedstock cost compared to using only pulpwood at $116.73/ton.  In addition, available biomass quantities were increased in the nine county area through the use of logging residues by 380,000 tons per year.