Experimental study on torrefaction of corn stover, switchgrass, and prairie grass

Biomass is known as the only source for production of renewable liquid transportation biofuels. Lignocellulosic biomass has an advantage over other biofuel feedstocks, such as corn starch, soybeans, and sugar cane, because it can be produced quickly and at significantly low cost but not to compete to food crops. Nonetheless, transportation and storage are still big issues for sending lignocellulosic biomass feedstocks to bio-refinery facility to be converted into biofuels due to their low bulk density, high moisture, and biodegrading properties. The presenting study was trying to address those issues by torrefaction pretreatment. Torrefaction of corn stover, switchgrass, and prairie grass was carried using a lab scale batch reactor. The reactor was heated up to the selected temperature (250°C, 300°C, or 350°C) and kept at the final temperature for a period of 3 hours. The effect of raw materials and temperatures on the properties of the torrefied products (solid biochar, liquid bio-oil, and gaseous syngas) was analyzed. These products were characterized with heating value, pH value, moisture content, etc. The heating values of bio-char increased with temperature of torrefaction while the yields on a weight basis decreased. The bio-chars produced have hydrophobic properties and higher heating values than the raw materials.