Farm-Scale Biomass Pelletizer Performance for Switchgrass Pellet Production

摘要

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 small scale pelletizer;suitable for on-farm use (-70 kg hr-1 rated output). Ground switchgrass (Panicium 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 pelletquality 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) followed by the actual feedstock mixture. The highest quality pellets were obtained from switchgrass with a moisture content ranging from 11 to 17% (wet basis). Adding between 1% and 4% vegetable oil improved pelletquality slightly; while adding starch to the switchgrass feedstock did not yield noticeable improvements. Power consumption by the pelletizer averaged 0.22 kwh per kg for feedstock at 14% moisture and 1% oil; but dropped to 0.16 kwh per kg when the oil content was increased to 5%. Reducing the operating speed of the pelletizer resulted in improved quality of the pellets.