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11.09

Introduction

Biofuels such as biodiesel and ethanol have recently emerged as potential solutions to achieving long-term sustainability in the transportation sector. In certain forms, utilizing certain pathways, biofuels can be nearly carbon neutral while consuming only a small fraction of the quantity of fossil fuels consumed today. Yet, there are a number of challenges which must be overcome if biofuel vehicles are to ever penetrate mainstream transportation markets. Two such challenges are addressing the total fuel-cycle emissions of biofuel pathways and developing adequate transport, distribution and infrastructure systems for biofuel processing and delivery. This is the second article in an ongoing series on biofuels for transportation; this article provides a discussion on the two aforementioned biofuel challenges.

Emission Impacts of Biofuels

One often-used indicator of biofuel emissions is the “carbon requirement,” which is the total carbon dioxide (CO₂) emissions from a biofuel technology, excluding those captured by the cultivation of the original source of biomass, divided by its specified energy output, measured in kilograms of CO₂ per megajoule (kg CO₂/MJ). Simply, the carbon requirement is the carbon dioxide output per delivered energy output, considering the tail pipe only (Elsayed et al., 2003). A 2003 study by Sheffield Hallam University in the United Kingdom found that the carbon requirements for biofuels varies considerably depending on the type of fuel and feedstock. Figure 1 presents the carbon and total greenhouse gas requirements for various biofuels along with reference results for a relevant sample of conventional sources of energy.

Figure 1: Carbon and Greenhouse Gas Requirements (click to enlarge)

Data Source: Elsayed et al.  (2003)

The results show that biofuels not only produce considerably less emissions on a CO₂/MJ basis when compared to regular gasoline and ultra low sulfur diesel, but emissions also vary greatly depending on the type of fuel and feedstock considered. Excluding ethanol from wheat straw, which has an uncharacteristically low carbon profile, the carbon requirement differs by a factor of nearly threefold from the lowest- to highest-polluting biofuel type. In terms of total greenhouse gas requirement, biodiesel from oilseed rape is the most polluting biofuel considered by the authors, but still produces about half of the total greenhouse gases of gasoline or ultra low sulfur diesel.

 The carbon requirement methodology is heavily flawed, however, due to its lack of inclusion of feedstock-stage carbon sequestration benefits. That is, the carbon requirement measurement does not consider the carbon captured by the cultivation of the original source of biomass. A prominent transportation analysis methodology which does capture the feedstock stage is the total fuel-cycle analysis (TFCA). TFCAs typically separate emissions into two components: upstream emissions and downstream emissions. Upstream emissions include emissions from all activities associated with recovering and transporting fuel feedstock, as well as refining, storing, and delivering fuel to refueling stations  (Winebrake et al., 2000). Upstream activities are typically separated into two groups: feedstock-related stages and fuel-related stages. Downstream emissions include emissions from vehicle refueling and operation, and are sometimes referred to as vehicle operation stages (Winebrake et al., 2000). Each stage in a fuel-cycle includes activities that produce GHG and criteria pollutant emissions. “These emissions are typically caused by fuel combustion during a particular stage, although some noncombustion emissions occur (e.g., natural gas emissions from pipeline leaks and evaporative losses in refueling.)” (Winebrake et al., 2000, p. 103).

The most widely-used tool for determining total fuel-cycle energy use and emissions is the Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) model developed by Argonne National Laboratory. GREET is an Excel-based model which includes more than 100 fuel production pathways and more than 70 vehicle/fuel systems. The model calculates consumption of total energy, fossil fuels, petroleum, coal, and natural gas; emissions of CO₂-equivalent greenhouse gases; and emissions of six criteria pollutants (anl.gov, 2008). To demonstrate the importance of including the impact of the feedstock stage when discussing biofuel emissions, here the results of a simplified GREET simulation are presented. The simulation reveals that on a well-to-wheels fuel-cycle basis, some biofuels demonstrate tremendous environmental advantages over gasoline or diesel vehicles—advantages far in excess of those shown by Elsayed et al. in their carbon requirement analysis. Figure 2 presents the results of a simplified GREET simulation for vehicles utilizing gasoline, conventional diesel, two grades of biodiesel (from soy beans), two forms of ethanol (from corn and sugar cane biomass), gasoline vehicles with a low-level ethanol blend (E15), and methanol vehicles.[1]

Figure 2: Fuel-Cycle Greenhouse Gas Emissions (click to enlarge)

As is evident in the figure, on a total fuel-cycle basis, vehicles using a pure biodiesel blend (i.e. BD100 or soyoil), produce a fraction the amount of emissions produced from gasoline or diesel vehicles. E85 vehicles using sugar cane as a feedstock produce about half as many emissions as gasoline vehicles, and even E85 with corn as a feedstock have substantial emissions benefits over gasoline vehicles. If one were to consider only the downstream emissions, biofuels, although showing some promise, would not look nearly as promising as when the total fuel-cycle is considered. The bottom line is that carbon neutrality of biofuels depends heavily on feedstock selection.

A critical concern that is not captured in GREET analyses, nor in most fuel-cycle analyses, is the emissions impact of converting forests and grasslands into cropland for the production of biofuels. While not a major issue in the United States due to the country’s plentiful existing farm lands (and strictly protected forests), land conversion is a prominent issue in many developing nations. Deforestation and land conversion will be discussed in full depth in a later installment of this series on biofuels, but as a precursor, consider the following brief discussion on the emissions impact of converting forests and grasslands into cropland.

In a recent study, Searchinger et al. (2008) found that the greenhouse gas savings from corn-based ethanol would equalize and therefore “pay back” carbon emissions from land-use changes in 167 years, meaning GHGs increase until the end of that period. This is based on an increase in ethanol usage by 56 billion liters (14.8 billion gallons) and an increase in farm land of 10.8 million hectares (26.7 million acres). According to the authors, over a 30-year period, counting land-use change, GHG emissions on a per-mile basis from corn ethanol is nearly double those from gasoline. The authors further found that even if corn ethanol caused no emissions except those from land-use change, overall GHGs would still increase over a 30-year period. The authors argue that in Brazil, if displaced ranchers convert rainforest to grazing land, the payback period could rise to 45 years. Thus, by including the carbon impact of land use changes, the authors show that biofuels are extremely polluting versus gasoline vehicles.

Hence, there are multiple methods for considering the emissions impacts of biofuel vehicles and each method has its own set of flaws. Although fuel-cycle analyses are likely the most common, this type of analysis often neglects the important carbon impacts of land-use changes, which have been found to potentially be extremely substantial. While the fuel cycle analysis may show an overall decrease in carbon emissions, the land-use changes could entirely cancel out the benefits of the lesser-polluting fuel cycle of biofuels.

Biofuel Infrastructure

A report by the U.S. Congressional Research Service says that there are significant barriers to developing the expanded infrastructure needed to deliver a greater quantity of biofuels to the market . The report explains that expanding production of ethanol will likely strain existing fuel supply infrastructure, and in some cases entirely new infrastructure will be necessary to handle a high percentage of ethanol in gasoline.

The report further explains that there are critical distribution issues with biofuels that have yet to be addressed, such as the fact that ethanol-blended gasoline tends to separate in pipelines causing delivery problems, and that ethanol is corrosive and may damage existing pipelines. Thus, unlike petroleum products, ethanol and ethanol blended gasoline cannot be shipped by traditional pipelines in the United States. Even if the fuel could be widely distributed by pipeline, the authors point out that ethanol must be moved from rural areas in the Midwest to more populated areas, which are often located along the coasts. This shipment is in the opposite direction of existing pipeline transportation, which moves gasoline from refiners along the coast to other coastal cities and into the interior of the country.

According to a Wall Street Journal article, due to the fact that ethanol cannot be transported by pipeline in the United States, increased ethanol production is straining railroads already taxed by the burgeoning shipments of coal, containers and grain (Brat and Machalaba, 2007). The authors quote the Association of American Railroads and point out that ethanol shipments via rail have increased substantially, nearly tripling from 2001 to about 106,000 rail carloads in 2006 and increasing to at least 140,000 in 2007.

One possible solution is to upgrade the U.S. pipeline infrastructure by coating the interior of the pipelines with epoxy or some other corrosion-resistant material. Alternatively, pipeline operators could replace all susceptible pipeline components with more durable pieces. However, either option would be an extremely costly endeavor, thus raising the price of the fuel for the end-consumer.

Elsewhere, the problems are not as severe. Bomb et al. (2007), for example, argue that in Europe it is feasible for bioethanol (from sugar and starch) and biodiesel to use the distribution infrastructure designed for gasoline and diesel with no major changes. The authors maintain that biodiesel can use the transport, storage and retail systems of diesel, but bioethanol faces a few difficulties. To avoid some problems, Bomb et al. argue, bioethanol can be converted to ethyl tertiary butyl ether (ETBE) and then blended with gasoline, but this is also a complex and expensive procedure.

Conclusion

This article has discussed two major challenges with biofuel development for transportation systems, namely, the carbon and emissions debate, and the availability or lack thereof, of adequate production and distribution infrastructure. While no emissions-measuring method has proven itself as ultimately superior, analyses of carbon requirements and total fuel-cycle emissions show most biofuels to be cleaner than gasoline. However, inclusion of land-use impacts can completely cancel out such cleanliness, and prove biofuels to be even worse environmentally than gasoline. Moreover, infrastructure issues are substantial for biofuels, with numerous analyses showing that the United States is simply not ready to produce or distribute biofuels on a large-scale. Whether to fortify the current infrastructure or construct new systems from scratch, the investments required to allow biofuels to further penetrate mainstream transportation markets will be immense. In the next installment of this series, a dialogue will be provided on issues of land availability, deforestation and land conversion.

 References

 anl.gov. (2008). The Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) Model. Argonne, IL: Argonne National Laboratory. Retrieved 24 September, 2009, from http://www.transportation.anl.gov/modeling_simulation/GREET/index.html

Bomb, C., McCormick, K., Deurwaarder, E., & Kaberger, T. (2007). Biofuels for transport in Europe: Lessons from Germany and the UK. Energy Policy, 35, 2256-2267.

Brat, I., & Machalaba, D. (2007). Can Ethanol Get A Ticket To Ride? New York, NY: Wall Street Journal. Retrieved 28 September, 2009, from www.trademarkplasticscorp.com/images/Can%20Ethanol%20Get%20a%20Ticket%20to%20Ride.pdf (free PDF version)

Elsayed, M. A., Matthews, R., & Mortimer, N. D. (2003). Carbon and Energy Balances for a Range of Biofuels Options. Sheffield, UK: Resources Research Unit, Sheffield Hallam University.

Searchinger, T., Heimlich, R., Houghton, R. A., Dong, F., Elobeid, A., Fabiosa, J., et al. (2008). Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change. Science, 319, 1238-1240.

Winebrake, J. J., Wang, M. Q., & He, D. (2000). Toxic emissions from mobile sources: A total fuel-cycle analysis for conventional and alternative fuel vehicles. Paper presented at the 93nd Annual Meeting of the Air and Waste Management Association, Salt Lake City, UT.

Yacobucci, B., & Schnepf, R. (2007). Ethanol and Biofuels: Agriculture, Infrastructure, and Market Constraints Related to Expanded Production. Washington, DC: US Congressional Research Service.

Patrick E. Meyer is a doctoral student and research associate at the University of Delaware’s Center for Energy and Environmental Policy and is also a research associate with Energy and Environmental Research Associates, LLC., Pittsford, New York, specializing in energy and environmental life-cycle analysis. Meyer also serves on the IEEE-USA Communications Committee and is IEEE-USA Today’s Engineer Energy, Environment & Sustainability Editor.

Comments may be submitted to todaysengineer@ieee.org.