Biomass pelleting experiments were designed to conduct single-pelleting of non-treated and steam exploded barley, canola, oat and wheat straw grinds obtained from 6.4, 3.2, and 1.6 mm hammer mill screen sizes by applying pressures of 31.6, 63.2, 94.7, and 138.9 MPa using a close-fit plunger die assembly (die length 135.3 mm and diameter of 6.30±0.5 mm).  Subsequently, pilot scale pelleting of non-treated and steam exploded straw was performed based on the conclusions derived from single-pelleting experiments.  The quality of pellets from close-fit plunger die assembly was ascertained by measuring their respective density and durability.  In addition, change in pellet density was measured after a storage period of one month to ascertain its dimensional stability.  The density of pellets from non-treated and steam exploded agricultural straw significantly increased with an increase in applied pressure at any specific hammer mill screen size.  The pellet density of steam exploded straw grinds at any specific hammer mill screen size and pressure was significantly higher than non-treated straw grinds.  At any specific hammer mill screen size, the durability of pellets from non-treated straw grinds did not show any significant change with an increase in applied pressures.  However, durability of pellets from non-treated straw grinds significantly decreased with a decrease in hammer mill screen size from 6.4 to 1.6 mm at any specific applied pressure.  High durability values (>80%) were observed for pellets of non-treated straw grinds at 6.4 mm hammer mill screen size and for pellets from steam exploded straw grinds at all hammer mill screen sizes and applied pressure levels.

During pilot scale pelleting, customization of grounds straw material was also performed by adding steam exploded biomass in increments of 25% to non-treated ground straw for respective biomass at specific grind size.  In addition, the straw samples were ground using 0.8 mm hammer mill screen size to improve their flowability through the pellet mill.  Subsequently, the straw samples were conditioned to 17.5% moisture content and 10% flaxseed oil content to increase the bulk density and flowability of grinds, which resulted in the production of pellets.  The steam conditioning of straw grinds during pelleting was not performed in order to minimize energy input.  The pellet mill produced pellets from ground non-treated straw at hammer mill screen sizes of 0.8 and 1.6 mm and customized samples having 25% steam exploded straw at 0.8 mm.  However, the steam exploded ground straw did not produce pellets.  In general, density of pellets increased with a decrease in screen size from 1.6 to 0.8 mm.  However, no significant differences in density values were observed for non-treated samples at 0.8 mm and customized samples.  Bulk density of straw pellets significantly varied with grind size and customization, and was found highest for customized straw.  The durability of pellets significantly increased with a decrease in grind size for non-treated samples from 1.6 to 0.8 mm.  However, the addition of steam exploded straw to non-treated straw at 0.8 mm screen size significantly decreased the durability.  The durability of pellets was negatively correlated to pellet mill throughput and was positively correlated to specific energy consumption.