Utilization of mechanical separations to reduce the cost of ash reduction in corn stover in the feedstock supply chain

The viability of conversion facilities depends on feedstock supply systems that ensure low-cost, high-volume feedstock supplies, which meet the quality requirements of the conversion technology.  One feedstock component that significantly affects feedstock and product quality is ash, which is comprised of “physiological ash,” which is unevenly distributed among plant tissues depending on their function, and non-physiological ash or “introduced ash” from dust and contaminating soil.  The Biochemical platform has specified a 5 wt% ash specification to provide minimum conversion efficiency and process costs.  Mechanical separations can take advantage of the differences in ash content and composition among tissue types to reduce the amount of the biomass that must be chemically treated to meet this ash specification.  Anatomical fractions of corn stover were collected, ground to pass a ¾” screen, and size separated with 6 sieves ranging from 0.150-9.5mm.  The size fractions were analyzed for ash content and composition.  The majority of particles <0.6 mm originated from sheaths and husks, while the cobs particles were primarily >9.5mm.  Ash content was highest in the smallest size fractions, with leaf fractions <0.150 mm containing 69% ash.   LIBS analysis indicated uneven distribution of ash components among both anatomical fractions and size fractions.  The ash content of size fractions >2mm (84% of the biomass) already meet the ash specification.  The size fractions smaller than 2mm (16%) are the only biomass requiring chemical treatments to reduce the ash content.  This reduction in the amount of biomass needing treatment represents a significant savings in process costs.