Farm-Scale biomass pelletizer performance for switchgrass pellet production

The impact of feedstock characteristics (moisture content, additive content) and operational parameters (die temperature, pelletizer speed) on pellet quality, plugging tendency, and pelletizer energy use was investigated for a smallscale pelletizer, suitable for on-farm use (∼70 kg h-1 rated output). Ground switchgrass (Panicum virgatum) was prepared in small (<1 kg) batches and run through a flat plate, rotating die pelletizer with 6 mm die holes and a die thickness of 25 mm. The resulting pellet quality and die flow (plugging tendency) were assessed using a subjective pellet quality scale. Results indicate that successful pelleting conditions were most consistently achieved by using a "premix" consisting of ground switchgrass and Distillers Dried Grains in a 3:7 ratio (mass basis) to condition the die, followed by the actual feedstock mixture. The highest quality pellets were obtained from switchgrass with a moisture content ranging from 12% to 18% (wet basis). Adding between 1% and 4% vegetable oil improved pellet appearance, while adding starch (1% To 5%) to the switchgrass feedstock did not yield quality improvements. Reducing the operating speed of the pelletizer resulted in improved quality of the pellets. Feedstock moisture content was positively correlated to pellet production rate and negatively correlated with pelletizer energy use.