Densification of biomass using a pilot scale flat ring roller pellet mill

The production characteristics from a pilot scale flat ring die pellet mill were evaluated for four different biomass materials (miscanthus, corn stover, switchgrass, and wheat straw) to determine the effect of moisture preconditioning upon pelletization. The moisture content of the material entering the pellet mill was 10%, 15%, 20% and 25% for miscanthus, switchgrass, and wheat straw; while, only 15%, 20%, and 25% moisture content was evaluated for corn stover. For miscanthus, switchgrass, and wheat straw at the highest moisture content (25%), pellet formation was readily achieved with the percentage of pellets produced being 92%, 92%, and 96%, respectively. Corn stover preconditioned to a moisture content of 15% resulted in the highest rate of pellet formation, lowest specific energy requirement, and similar durability to other measured moisture contents. For the differing biomass materials, the specific energy requirements for the flat ring pellet mill was measured and varied between 101 to 324 kWh/Mg depending on the crop and moisture content. With energy consumption being one of the primary costs of pelletization, the on-farm/localized pelletization of biomass using a flat ring die pellet mill may be impaired by the high specific energy requirements of pelletization relative to other pellet mill designs.