Abstract
To meet Energy Independence and Security Act (EISA) cellulosic biofuel mandates, the United States will require an annual domestic supply of about 242 million Mg of biomass by 2022. To improve the feedstock logistics of lignocellulosic biofuels in order to access available biomass resources from areas with varying yields, commodity systems have been proposed and designed to deliver quality-controlled biomass feedstocks at preprocessing “depots”. Preprocessing depots densify and stabilize the biomass prior to long-distance transport and delivery to centralized biorefineries. The logistics of biomass commodity supply chains could introduce spatially variable environmental impacts into the biofuel life cycle due to needing to harvest, move, and preprocess biomass from multiple distances that have variable spatial density. This study examines the uncertainty in greenhouse gas (GHG) emissions of corn stover logistics within a bio-ethanol supply chain in the state of Kansas, where sustainable biomass supply varies spatially. Two scenarios were evaluated each having a different number of depots of varying capacity and location within Kansas relative to a central commodity-receiving biorefinery to test GHG emissions uncertainty. The first scenario sited four preprocessing depots evenly across the state of Kansas but within the vicinity of counties having high biomass supply density. The second scenario located five depots based on the shortest depot-to-biorefinery rail distance and biomass availability. The logistics supply chain consists of corn stover harvest, collection and storage, feedstock transport from field to biomass preprocessing depot, preprocessing depot operations, and commodity transport from the biomass preprocessing depot to the biorefinery. Monte Carlo simulation was used to estimate the spatial uncertainty in the feedstock logistics gate-to-gate sequence. Within the logistics supply chain GHG emissions are most sensitive to the transport of the densified biomass, which introduces the highest variability (0.2–13 g CO2e/MJ) to life cycle GHG emissions. Moreover, depending upon the biomass availability and its spatial density and surrounding transportation infrastructure (road and rail), logistics can increase the variability in life cycle environmental impacts for lignocellulosic biofuels. Within Kansas, life cycle GHG emissions could range from 24 g CO2e/MJ to 41 g CO2e/MJ depending upon the location, size and number of preprocessing depots constructed. However, this range can be minimized through optimizing the siting of preprocessing depots where ample rail infrastructure exists to supply biomass commodity to a regional biorefinery supply system.
Highlights
Post-industrialized economies rely on energy for almost all fundamental needs including food production, heat, transportation, manufacturing, and communication
The average corn stover-to-ethanol life cycle greenhouse gas (GHG) emissions for the two scenarios we examine in Kansas (Table 3) are 26 g CO2e/MJ ethanol and 25 g CO2e/MJ ethanol for Scenarios 1 and 2, respectively, 66% and 63% of the conventional system’s life cycle GWP
Estimates ranging from 3 g CO2e/MJ [35] to 17.5 g CO2e/MJ [47], aggregate energy input for both collection and harvest were larger than our study findings, suggesting that the GWP for the logistics supply chain will depend on equipment performance, including energy efficiency and age
Summary
Post-industrialized economies rely on energy for almost all fundamental needs including food production, heat, transportation, manufacturing, and communication. The use of fossil fuels have enabled large-scale industrial development, but growing concerns regarding energy security and the environment, climate change, have inspired the development of mandates for renewable energy from wind, biomass, and solar energy sources. Independence and Security Act (EISA) of 2007 requires that 61 billion L/year cellulosic ethanol replace petroleum-based transportation fuels. To meet this demand, an estimated 242 million Mg/year of biomass will need to be supplied to biorefineries that can process lignocellulose [1]. Sufficient biomass supply has been identified to meet these requirements through large-scale national assessments [2], and research is on-going concerning the logistics required to cultivate, harvest, transport, and process such large quantities of biomass into fuel. Our study focuses on the supply and logistics chain of the lignocellulosic ethanol produced from corn stover, an agricultural residue
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