ECONOMIC AND ENVIRONMENTAL IMPLICATIONS OF CORN STOVER DENSIFICATION OPTIONS FOR BIOFUEL IN MINNESOTA

Low bulk density of corn stover and associated transportation needs have been recognized as an obstacle for large-scale utilization of corn stover for biofuel feedstock. Densification of corn stover reduces transportation needs, while it also demands additional energy and incurs costs. The merit of densification is also subject to the mode of transportation and distance, which in turn depends on the size of biorefineries. In this study, cost and CO2 emission implications of grinding and pelletizing corn stover for ethanol production are examined. Five different logistics scenarios are compared based on conditions in Minnesota, where truck/rail transportation, handling, and processing costs and associated CO2 emissions are calculated for various biorefinery capacities. Pelletizing options are the least-cost option for biorfineries larger than 277 million liters of annual capacity (MLY), while the round bales via truck option is the least-cost option for biorfineries smaller than 277 MLY. However, pelletizing options generally exhibit poorer performance in terms of their CO2 emissions. Ground corn stover via rail generates the least CO2 emissions for biorefineries larger than 130 MLY. For smaller ethanol plants, the round bales via truck option is found to be the most favorable option from the CO2 emission perspective. The results show that pelletizing is economically attractive for mid-size to larger biorefineries, while environmentally unattractive due to its large electricity use regardless of the size of biorefinery. The analysis shows a clear trade-off between environmental and economic objectives, and highlights the needs of addressing the high energy consumption of the pelletizing process.