Fast Pyrolysis of Stored Biomass Feedstocks

Abstract

Biomass pyrolysis oils were produced from stored biomass feedstocks by rapid pyrolysis in a fluidized bed reactor. The feedstocks used for these studies were switchgrass, corn stover, and hybrid poplar. The woody and herbaceous feedstocks were stored in chip piles and bales, respectively, unprotected in an open field for 6 months. At the end of the storage period, biomass samples were taken from the interior of bales and the centers of chip piles for pyrolysis studies. The materials were ground to pass -20/+80 mesh and dried to less than 10% moisture content before pyrolyzing in the fluidized bed reactor. Pyrolysis was conducted at 500 °C and with less than 0.4 s apparent vapor residence time. Total liquid yields were as high as 66% for the hybrid poplar and as low as 58% for the corn stover. Moisture content of the oils was between 10 and 13%. Gas and char/ash yields were 10-15% and 12-22%, respectively. The char/ash yields were feedstock dependent, but storage influence was significant for only the corn stover feedstock. Gas and liquid yields were not influenced by storage time. The oils were highly oxygenated and had higher heating values (HHV) of 23-24 MJ/kg that decreased slightly with storage time for all the feedstocks except the switchgrass. The oils, as currently produced, are high in ash and alkali metals. Ultimately, they may be upgraded and used as boiler and turbine fuels.