Study Concludes That Large-Scale Transport of Ethanol Could Negate Its Economic and Environmental Benefits Compared to Gasoline
|Emissions from ethanol transport in the CMU study applied to ethanol life cycle emissions from other studies. Emissions from transport are recalculated using the CMU results. Click to enlarge.|
A new study by researchers at Carnegie Mellon University (CMU) concludes that the emissions associated with the transport of ethanol could negate its potential economic and environmental benefits compared to gasoline. Emissions from ethanol transport estimated in the new work are up to two times those for ethanol transport in previous life cycle analysis studies.
To reduce economic and environmental costs, the CMU team recommends regional concentration of E85 blends for future ethanol production and use. An open-access paper on the study was appeared online 25 February in the ACS journal Environmental Science & Technology.
The rapid growth of ethanol production and use in the US has major infrastructure implications. In addition to the construction of additional production capacity, transportation of feedstock to biorefineries and of ethanol to markets will result in an increase in transport demand. Ethanol will be primarily produced in the midwest and will need to be transported long distances to major demand centers on the coasts. Increases in ethanol production will result in shifting transportation demand for corn, biomass feedstocks, ethanol, and byproduct, which will affect rail, barge, and truck transportation. The growth of the ethanol market and transportation demands must also compete with significant growth in other major freight transport categories.—Wakeley et al. (2009)
|Ethanol distribution model. Credit: ACS. Click to enlarge.|
The study by Chris Hendrickson and colleagues builds upon other research that indicated that ethanol transport costs in an optimized system, at $0.02/L of E16, are an order of magnitude greater than equivalent transport costs for gasoline, at $0.003/L. The new paper considers the effects of feedstock prices and transport on ethanol production costs, national distribution of an E85 blend for three production scenarios, and environmental impacts by presenting a comparative analysis for nationwide production and distribution systems of corn and cellulosic ethanol in the US. The three scenarios are:
Near Term Corn Ethanol is a baseline scenario that considers the production and distribution of 57 billion liters (15 billion gal) of corn ethanol, corresponding to current mandated upper limit of corn ethanol production in the US by EISA 2007. This amount of fuel production represents 8% of light duty gasoline consumption in 2006, calculated on an energy basis.
The EISA Biofuel Mandate for 2022 scenario considers the production and distribution of 136 billion liters of ethanol, with 57 billion liters of corn ethanol. For this analysis, it was assumed that the remainder would be supplied by cellulosic ethanol produced from switchgrass, though the mandate requires only 60 billion liters of cellulosics while the remainder could come from other advanced biofuels.
The Large Scale Cellulosics scenario considers large-scale production of cellulosic ethanol, for a total of 268 billion liters (70 billion gal) of ethanol.
Some 95% of greenhouse gas emissions from distribution result from fuel combustion, with the distribution of the ethanol from production facilities, whether by truck or rail, contributing the largest amount of emissions. The study did not consider the potential use of pipelines. The study found that, in an optimized model with full market penetration of E85, more than 70% of the ethanol would be transported by truck, with an average distance of 110 km. Of the remaining 30%, very little would be expected to travel by barge due to the competition with rail.
Transportation emissions calculated in this study for a large-scale ethanol production and distribution system could have a significant impact on life cycle emissions. Average estimated transport emissions agree with those in previous studies; however, there is a large range of emissions, depending on transport distances. Additional transportation requirements for cellulosic ethanol feedstock, similar to those for corn, could result in a doubling of total life cycle emissions if rail is not utilized. Transportation distances and emissions presented in the literature are applicable for regional ethanol production and distribution. However, they are not appropriate for long distance ethanol and/or feedstock distribution requirements, which are representative of a more realistic, nonoptimal nationwide ethanol system.
...This analysis assumes that ethanol will be produced and distributed in an optimized system designed to minimize costs. The actual system will likely have both higher costs and emissions, particularly if transport congestion is considered. Many factors could influence production and end market locations, including state and local government incentives and mandates. The analysis emphasizes the importance of regional alternative fuel strategies. Ethanol should be pursued in areas near feedstock production, while different transportation fuel alternatives, such as plug-in hybrids, should be explored in other areas remote from feedstock sources.—Wakeley et al. (2009)
Heather L. Wakeley, Chris T. Hendrickson, W. Michael Griffin and H. Scott Matthews (2009) Economic and Environmental Transportation Effects of Large-Scale Ethanol Production and Distribution in the United States. Environ. Sci. Technol., Article ASAP doi: 10.1021/es8015827