Estimates of dry matter losses during harvest and storage of herbaceous biomass are needed to determine harvest efficiency and net biomass yield. Losses of switchgrass (Panicum virgatum L.) biomass stored in large round bales as affected by protected and unprotected conditions in three experiments during 1992 to 1995. We also measured the losses of dry matter (DM) during the harvesting operation each year and determined the quantity and quality of runoff water from stored bales during one year. In Experiment 1, “Alamo” switchgrass was harvested in August 1992 and stored in 275 kg bales unprotected outside on a grass sod for six months. In Experiments 2 and 3, switchgrass was harvested in November of 1993 and 1994, respectively, and stored in 370 kg bales for one year inside on concrete, outside on a grass sod unprotected from the elements, or outside on a gravel pad. In each experiment, the biomass was field dried to 11 to 19% moisture and baled. The bales were weighed at the beginning and end of the storage period to determine DM losses. In Experiment 1, DM losses during six months of storage were 13% of the original bale dry weight. In Experiments 2 and 3, there were no differences (P > 0.05) in DM losses (average of 5%) among outside treatments during the 12 months of storage. There were no biomass losses for bales stored inside in Experiment 2; however, there was a 2% loss in Experiment 3. Losses of DM during baling ranged from 1 to 5% depending on moisture concentration in the biomass at baling. Larger losses were associated with drier biomass, presumably because of more shattering. Quality and quantity of runoff water from bales were not different (P > 0.05) from runoff water of control plots.

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 degrees C and with less than 0.4 s. 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 will be upgraded and used as boiler and turbine fuels.

'Alamo' switchgrass (Panicum virgatum L.) was harvested in two different years and stored as large round bales, unprotected outside, for 26 weeks. Fresh and scored switchgrass samples were analyzed for their structural and non-structural constituents. These summative analyses of the switchgrass showed differences in the composition of materials harvested at different rimes and indicated that the compositions changed during storage.On a dry weight, whole biomass basis, significant differences were observed in the extractives (+3%), ash (+1%), hemicelluloses (-1.4%), and cellulose (-4%) components of the switchgrass harvested in October 1991 relative to August 1992. The bales from the switchgrass harvested in October 1991 were exposed to high rainfall (65 cm) during storage and experienced much greater weathering than bales from the second harvest. The largest change in composition occurred in the ethanol-extractable component. The switchgrass showed a significant loss of extractives in both the weathered outer layer (11%) and the unweathered inner fraction (8%) of the bales prepared from the first harvest. Switchgrass harvested in August 1992 underwent much smaller compositional changes compared to the October 1991 harvest.The extractives in switchgrass and other grasses may contain substantial amounts of fermentable carbohydrates. If so, their loss during storage could have a significant impact on the conversion of switchgrass into ethanol. This is an example of the feedstock assessment research being conducted to determine the influence of harvest and storage conditions on the thermochemical and biochemical conversion of various biomass feedstocks into fuels and chemicals. The results of this research are expected to provide a guide to agricultural practices that optimize production of feedstocks for conversion into fuels. (C) 1996 Elsevier Science Ltd.

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 degrees 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.

Thermochemically converting biomass feedstocks to fuels is one of the major thrusts of renewable energy research at the National Renewable Energy Laboratory. Among several thermochemical routes is the fast pyrolysis process which produces liquid fuels from woody and herbaceous biomass feedstocks. Because of the large variability in the composition of biomass feedstocks due to plant variety and environmental factors, it is important to assess how these variabilities affect the properties of thermochemical liquid fuels (bio-oils) produced from these resources. Similar varieties of switchgrass (Panicum virgatum L.) that were grown at three different locations and three hybrid poplar clones that were grown at one location were used in these studies. The feedstocks were pyrolyzed in a fluidized bed reactor at 500{degrees}C. The gas products were analyzed on-line and the liquid products were analyzed for elemental composition and higher heating values. Apart from small difference in the yield of char/ash, the yields of pyrolysis oils and gases were similar for switchgrass feedstocks grown at all three locations. The char/ash yields ranged from 21.1 to 22.9%; total liquids (organic liquids + water) yields ranged from 59%-60.5%; and the gas yields ranged from 11%-12% (wt). The higher heating values (HHVs) of the oils weremore » similar (24.3-24.6 MJ/kg). For the hybrid poplar feedstocks, total liquids (65%-69%), char/ash (10%-11%), and gas yields (15.6%-17%) were similar for all three poplar clones; however, the elemental composition and the HHVs of the pyrolysis oils had statistically significant differences. The NC5260 pyrolysis oils had lower HHV (22.0{+-}0.5 MG/kg) compared to the DN clones (23.2{+-}0.3 MJ/kg). The yields of total liquids and organics for the three clones were higher than those for the switchgrass feedstocks. The gas yields for the hybrid poplar clones were higher than for the switchgrass, but had compositions similar to those of the switchgrass feedstocks.« less