Submitted to: Environmental Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/22/2011
Publication Date: 12/28/2011
Citation: Wilson, T., Mcneal, F.M., Spatari, S., Abler, D.G., Adler, P.R. 2011. Densified biomass can cost-effectively mitigate greenhouse gas emissions and address energy security in thermal applications. Environmental Science and Technology. 46(2):1270-1277. Interpretive Summary: There has been significant effort to quantify the life cycle greenhouse gas emissions for ethanol production from bioamss; however, little information is available describing the potential of densified switchgrass for reducing greenhouse gas emissions when used for heat and power generation. In this study, we measured the energy use from switchgrass seed to biomass production and quantified the net life cycle greenhouse gas emissions of densifying the biomass as pellets, cubes, and briquettes. We found that switchgrass harvest season, due to feedstock moisture content, and type of densified end product had the largest effect on greenhouse gas emissions. This information will help biomass crop producers and biomass conversion facilities meet their goals of producing a quality product with the greatest greenhouse gas benefits.
Technical Abstract: Determining the life cycle greenhouse gas benefits of biofuels has been critical for quantifying their potential for meeting governmental mitigation targets. Little work has been conducted to determine the life cycle greenhouse gas benefits of using biomass for heat or power generation, even though this pathway, like ethanol, could also lead to reduced oil imports. The objective of this study was to quantify energy use from switchgrass seed to biomass production and quantify the net life cycle greenhouse gas emissions of densifying the biomass as pellets, cubes, and briquettes. Each phase of biofuel production differs in which sources of greenhouse gases dominate the analysis. We found that mitigating for prior land use history and removing plant species previously occupying the field (e.g. row crops, pasture) was a significant source of greenhouse gas emissions during both seed production and switchgrass establishment for biomass production. During switchgrass production, soil nitrous oxide emissions became the most import source of greenhouse gases. However the dominate factors affecting the quantity of greenhouse gas emissions associated with the final product were switchgrass harvest season and the type of densified product. When replacing heating oil, switchgrass offset at least 40% more oil than conversion to ethanol.