Investigation of biochemical biorefinery sizing and environmental sustainability impacts for conventional bale system and advanced uniform biomass logistics designs

Abstract

The 2011 US Billion-Ton Update 1 estimates that there are enough agricultural and forest resources to sustainably provide enough biomass to displace approximately 30% of the country's current petroleum consumption. A portion of these resources are inaccessible at current cost targets with conventional feedstock supply systems because of their remoteness or low yields. Reliable analyses and projections of US biofuels production depend on assumptions about the supply system and biorefi nery capacity, which, in turn, depend on economics, feedstock logistics, and sustainability. A cross-functional team has examined optimal combinations of advances in feedstock supply systems and biorefi nery capacities with rigorous design information, improved crop yield and agronomic practices, and improved estimates of sustainable biomass availability. Biochemical-conversion-to-ethanol is analyzed for conventional bale-based system and advanced uniform-format feedstock supply system designs. The latter involves 'pre-processing' biomass into a higher-density, aerobically stable, easily transportable format that can supply large-scale biorefi neries. Feedstock supply costs, logistics and processing costs are analyzed and compared, taking into account environmental sustainability metrics.

Uncertainties in Life Cycle Greenhouse Gas Emissions from Advanced Biomass Feedstock Logistics Supply Chains in Kansas

“…With the exception of a recent study [18], most prior LCA studies of bio-ethanol [10,11,13,14,37] have assumed a conventional harvest and biomass delivery in bale format, resulting in relatively low (approximately 10%) net life cycle GHG emissions [11]. Here, we focus on identifying and characterizing uncertainties in advanced agricultural residue harvest, collection, storage, transport, pre-processing, and delivery operations to bio-ethanol facilities in the U.S. Midwest that arise due to variability in: (1) the sustainable harvest yield, defined as the quantity of corn stover removal set to maintain erosion and soil carbon within tolerable levels [2]; (2) transportation of the agricultural residue to depots that process and densify the biomass; (3) depot facility size, which influences equipment and energy throughput per unit of biomass; and (4) long-distance transport of the densified biomass delivered to the bio-ethanol facility.…”

“…The study also emphasized that the processing technology was critical to cost-reduction for the commodity system, a point also addressed by Shastri et al [16] and Uria-Martinez et al [17]. Recently, Argo et al [18] evaluated several environmental sustainability impacts (100-year global warming potential (GWP), rainfall (green water) and groundwater through irrigation (blue water) footprints), and costs for advanced logistics designs that employ densification steps for preprocessing agricultural residues and grasses in depots for long-haul transport to centralized biorefineries designed on the biochemical platform. Their results showed that the commodity system reduced both spatial and temporal variability and thus stabilized the cost of the feedstock logistics and supply chain.…”

“…For the counties we consider in Kansas, biomass marginal access costs begin at $40/ton and can be as high as $80/ton depending upon the available supply within each county. Wakeley et al [25] and Argo et al [18] varied biorefinery capacity in their studies in order to examine the range of transportation cost and GHG emissions. In this study, the biorefinery capacity was fixed at 800,000 dry matter tons (DMT)/year.…”

“…Argo et al [18] assumed in their model that the feedstock was transported from field to depot by semi-truck and from depot to biorefinery by rail given that railcars are capable of carrying a greater volume of goods with the minimal variable cost per mile. Thus, we assumed that distribution by truck is preferred for transport from field to depot, and rail is preferred for long distance transportation from depot to biorefinery.…”

“…The authors found that more than 300,000 tons of CO2e could be avoided if all unnecessary transportation were eliminated. Moreover, Argo et al [18] found that the logistics of the commodity system results in lower production costs than the conventional one when the biorefinery capacities are above 5000 Mg/day. A study by INL acknowledged that the transportation cost savings in the commodity system does not completely offset the costs associated with the pelleting and regrinding at all transport distances.…”