TORREFACTION OF RAW AND BLENDED CORN STOVER, SWITCHGRASS, AND PRAIRIE GRASS

摘要

Torrefaction is a promising thermal pretreatment process to prepare biomass for use in energy production. Torrefaction of corn stover, switchgrass, and prairie grass at three selected temperatures (250 degrees C, 300 degrees C, or 350 degrees C) for 3 h was carried out using a laboratory-scale batch reactor. Torrefaction of a blend of these three feedstocks at the same conditions was also examined. The effects of temperature and feedstock type on the yields and properties of the products (bio-char, bio-oil, and torrefaction off-gases) were analyzed. The bio-char produced from all of the feedstocks had higher carbon content and higher heating value (HHV) and lower moisture content (MC) when the torrefaction temperature increased. The HHV of bio-chars produced at 350 degrees C were 25.15 MJ kg(-1) for corn stover, 27.94 MJ kg(-1) for switchgrass, 28.75 MJ kg(-1) for prairie grass, and 28.79 MJ kg(-1) for the blend. The carbon contents of the bio-chars increased from 42.36% to 60.31% for corn stover, from 43.94% to 70.95% for switchgrass, from 44.27% to 66.28% for prairie grass, and from 43.52% to 64.47% for the blend with torrefaction at 350 degrees C. The results also indicated that the bio-oil and off-gases produced at lower temperatures had low value for further utilization. The MCs of the bio-oils produced in the torrefaction process were very high: 52.41% to 71.75% for corn stover, 58.01% to 74.22% for switchgrass, 65.44% to 75.07% for prairie grass, and 79.70% to 83.33% for the blend. The concentrations of combustible gases (H-2 and CO) in the off-gas were less than 12% for all feedstocks. Compared to the individual feedstocks, the blend exhibited a very limited synergistic effect. Blending different biomass species for torrefaction may be an option to produce a uniform feedstock for biofuel production.