Compression of Baled Cellulosic Feedstocks

Open Access
Hofstetter, Daniel William
Graduate Program:
Agricultural and Biological Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 09, 2011
Committee Members:
  • Jude Liu, Thesis Advisor
  • specific energy
  • power
  • indiangrass
  • energy
  • densification
  • corn stover
  • Bale compression
  • switchgrass
  • wheat straw
Over the next decade, a significant portion of the renewable fuels used in the United States will come from cellulosic feedstocks for biofuel production. A large percentage of these cellulosic feedstocks will come from agricultural residues and dedicated energy crops. Currently, two of the largest obstacles when dealing with cellulosic feedstocks are transportation and storage efficiency. Since they are not available year round, feedstocks for biofuel must be harvested when available and then transported and stored until needed for production. Due to their low bulk density, cellulosic feedstocks are expensive to transport long distances, and require a large volume of storage space. Biomass compression may offer an economically viable solution to these problems. Bales of corn stover, indiangrass, switchgrass, and wheat straw were compressed to determine their compression behavior in baled form. On average, the volume of all bales that were compressed was reduced by 67.4%. The baled crops follow a nonlinear density vs. pressure relationship that can be accurately predicted using an exponential equation. As loading speed increased, the energy, power, and specific energy required to compress the baled herbaceous biomass crops also increased. However, since each crop behaved differently during compression, the speed interaction was dependent on type of crop. To achieve a 60% reduction in bale volume at the slowest compression speed (2.54 mm/s), switchgrass required 15.6%, 61.7%, and 55.4% more energy than indiangrass, corn stover, and wheat straw, respectively. There were no significant differences in power or specific energy required at the slowest speed (α = 0.05). At the fastest compression speed (106.7 mm/s), switchgrass required 32.4%, 59.4%, and 73.0% more energy, 12.9%, 20.5%, and 27.0% more power, and 11.1%, 6.1%, and 19.3% more specific energy than indiangrass, corn stover, and wheat straw, respectively.