Biomass fractionation methods for ash removal: sieving, anatomical, and air classification

Pine forest residues are an important biomass feedstock for the thermochemical conversion platform.  The ash content of these residues decreases the efficiency of the conversion process, either through the presence of unconvertible material, or the degradation of catalysts and conversion products.  Three methods were used to separate loblolly pine forest residues into distinct fractions, and ash was measured in each fraction.  Ash was most concentrated in the lightest fractions obtained using air classification (8-15 wt%).  Sieving for size classification also yielded fractions elevated in ash content, with the smaller size fractions (>1.19mm) containing the highest concentrations of ash (2.3-6.0 wt%).  Anatomical fractionation proved to be least effective at concentrating ash, with the highest ash content found in the needles (2.2%) which made up less than 1.5% of the total biomass by weight.  Removal of these high ash fractions from the bulk of the biomass reduced the ash content of the remaining sample in all cases; however air classification was the most effective at concentrating the most ash in the least amount of biomass.  As an example, when the two air classified fractions with the highest ash content were removed, 41% of the ash was removed from the sample while removing only 6.7% of the biomass.  With the removal of these high ash fractions, the resulting ash content of the bulk sample was reduced from 1.69% to 1.07%.  Air classification is an effective ash reduction tool that can be used to enhance the quality of feedstocks for thermochemical conversion.