(604aj) Ash Reduction Methods to Provide Least Cost Feedstocks for Conversion Processes

Aston, J. E., Idaho National Laboratory
Lacey, J. A., Idaho National Laboratory
Westover, T. L., Idaho National Laboratory
Thompson, D. N., Idaho National Laboratory

Biomass contains inorganic constituents (referred to as ash) that inhibit downstream applications such as pyrolysis, combustion, gasification, and fermentation through various mechanisms.  Thus, the presence of ash adversely affects the value of feedstocks by increasing the required feedstock volumes, and/or by lowering the conversion yields of the feedstock for a given application.  This provides an economic driver to understand the cost/benefit relationships for ash removal.  

There are several ways to reduce the ash composition in feedstocks, including crop-harvest methods, mechanical separations, and chemical separations.  We will describe work investigating mechanical and chemical separations of southern loblolly pine that will contribute to a process cost model informed by the kinetic and thermodynamics of ash removal, and the subsequent unit operation requirements.  The nature of the data collected will allow this model to be independent of a given ash specification.  This work considers not only total ash reduction but the changes of the composition of the remaining ash, which effects various downstream applications differently.  Mechanical separations considered include sieving (size fraction separation) and air classification (density fraction separation).  Chemical separations considered include water leaching and acid leaching.  Initial data has identified the ash concentrations in mechanically sieved loblolly forest thinnings, and suggested that only specific fractions may require chemical treatment for the bulk material to meet potential specifications.