Drying, Grinding and Pelletization Studies on Raw and Formulated Biomass Feedstock's for Bioenergy Applications

Abstract

The United States has an abundant potential of biomass resources that can be used as bioenergy feedstocks; however, biomass in its raw, “as-harvested” form is not necessarily in a format (low bulk density and high moisture content) that meets the needs for the biofuel or bioenergy industry. Both high production and niche crops must be used together to meet the U. S. Department of Energy (DOE)’s goal to supply 36 billion gallons of renewable transportation fuels by 2022. To reach this goal, the United States must use more than just the common biomass sources such as corn stover, switchgrass, and other high production energy crops; it must also find ways to combine additional feedstocks as well. This study shows that the formulation of mixed feedstocks using niche and high production crops can produce feedstocks that meet the uniform format required by industry. Corn stover, switchgrass, lodgpole pine, and eucalyptus were combined during preprocessing followed by densification into pellets, resulting in a denser, higher energy value, more durable feedstock than the average of these fuels individually. This study also compares the energy consumption involved in preprocessing biomass. In the case of grinding energies for both Stage-I and Stage-II processes, corn stover and switchgrass consumed the least at about 19 and 34 kW hr/ton and 11 and 18 kW hr/ton, respectively, whereas the highest was both woody biomass types at about 94 and 43–49 kW hr/ton. The bulk density of pelletized blended feedstock is about 729 kg/m3 and is higher than what corn stover and switchgrass pelletized individually can achieve. The heating values are highest for woody biomass at about 18.37–19.30 MJ/kg and lowest for corn stover and switchgrass, which were both in the range of 16.74–16.97 MJ/kg. From these results, we can conclude that the physical and energy properties of blended feedstocks are better than just individually pelletized herbaceous biomass.