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What Are the Main Characteristics of Alternative Jet Fuels? 19 increases the chances that these technologies can reach commercial scale and add significant pro- duction to the alternative jet fuel supply pool. Furthermore, production costs for these technolo- gies are mostly driven by process maturity instead of feedstock cost, which is the case for HEFA. These technologies are still in the early stages of R&D and have yet to be tested in actual air- craft. As of this writing, flight programs are planned for both FTJ and CTJ. In the case of FTJ, a program is planned in Brazil in 2012 (see Table 1). In the case of the CTJ, the U.S. Air Force is teamed with Swedish Biofuels to execute a flight program on a Gripen fighter aircraft in 2014. Based on the pace of R&D and ASTM qualification activities as proven by the FT and HEFA experience, these fuels could be qualified in the 2013 to 2015 time period. Readers are advised to review the resources listed in Section 1.6 to stay current with these developments. How water intensive is the production of alternative jet fuel? Water use is a topic that frequently comes up during the discussion of alternative jet fuels. Depending on the specific way in which feedstocks are recovered and processed, water consump- tion for the production of alternative jet fuels may be comparable to or larger than the water amounts required for conventional jet fuel production (Stratton, Wong, and Hileman 2010). The water impact of alternative jet fuels should be evaluated by considering the feedstocks and conversion technologies separately. There are two water components pertaining to feedstocks: consumption and pollution. In terms of water consumption, traditional feedstock crops, such as soybeans, require large amounts of freshwater. In contrast, new bio-derived crops, such as switchgrass, do not need irrigation. Nontraditional crops like Camelina and Jatropha can grow in arid areas. Algae can grow in brackish water or seawater, which would limit the consumption of freshwater; however, freshwater needs also depend on the specific process used for algae growth and processing. In terms of water pollution, fossil feedstocks and traditional feedstock crops contribute runoff from fertilizers and pesticides. Regarding conversion technologies, the need for cooling is what drives water impact. The impact varies widely, from extensive to minimal, with the type of cooling and conversion technology. FT requires substantial cooling and is generally more water intensive than hydroprocessing per unit of energy produced. The water use of a HEFA facility is less than that of a Fischer-Tropsch facility. HEFA production involves the use of hydrogen, which in combination with the oxygen present in plant oil feedstocks produces net water from the process chemistry. What is carbon capture and sequestration? Carbon capture and sequestration involves capturing the gaseous CO2 released during a produc- tion process and storing it or converting it into other carbon compounds that are not released into the atmosphere. CCS technologies are being explored for manufacturing processes in which CO2 would be released into the atmosphere, such as the FT process to make alternative jet fuel. CCS will help lower the life-cycle GHG footprint of alternative jet fuels by preventing CO2 in the processing stage from being released into the atmosphere. Enhanced oil recovery, a process in which CO2 is injected into oil fields, is a known technology for carbon sequestration that has been used for decades (DOE 2011a). Research is being conducted to find more efficient means of capture, stor- age, and conversion. These include algal systems that could potentially convert the gaseous carbon dioxide into carbon-based compounds and carbon-based oils through photosynthetic activity. 2.4 Environmental Benefits of Alternative Jet Fuels What are the potential environmental benefits of alternative jet fuels? This handbook focuses on two main potential environmental benefits of alternative jet fuels. First, the overall life-cycle GHG footprint may be lower than that of conventional jet fuel. Second,
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20 Guidelines for Integrating Alternative Jet Fuel into the Airport Setting PM emissions may be lower. Reductions in NOx have been documented for alternative ground fuels relative to conventional diesel fuel, but there is currently no evidence to suggest that the same benefit extends to alternative jet fuels. The following sections discuss the GHG and PM benefits. What are the potential life-cycle greenhouse-gas benefits of alternative jet fuels? Compared with petroleum-based jet fuel, alternative jet fuels may have a lower GHG footprint when the entire life cycle of the fuel is considered. Life-cycle analysis (LCA) as it applies to jet fuel consists of estimating the amounts of various substances produced (or consumed) during the complete process of obtaining and using the fuel. This process is broken down into various stages as the fuel is transformed from its raw form, transported, and used. Appendix E contains a more detailed description of the life-cycle GHG analysis process. When reviewing the detailed LCA, consider the following observations: · The results depend greatly on the feedstock and the processing pathway to jet fuel; · There is substantial uncertainty in the impacts of land-use change, and this drives uncertainty in the overall GHG footprint; and · Best practices for such analysis are still evolving, particularly with regard to social equity (e.g., fuel-versus-food impacts). Are there estimates of life-cycle GHG footprints for different alternative jet fuel pathways? In order to illustrate the range of estimates that might be expected, we include results from a recent report (Stratton, Wong, and Hileman 2010) that analyzed several pathways to drop-in aviation fuels requiring no alterations in aircraft or storage facilities. Figure 2 shows the life-cycle GHG emissions for various combinations of feedstocks relative to conventional jet fuel. As Figure 2 shows, depending on assumptions (particularly those associated with land-use changes associated with growth of the feedstocks), these pathways were estimated to have life- cycle GHG emissions ranging from less than 1% of the conventional crude petroleum pathway to over 8 times greater than this pathway. Several pathways have estimated life-cycle GHG emis- sions that are less than half of that of crude to conventional jet fuel (switchgrass to FT fuel, Jat- ropha oil to HEFA, and Salicornia to HEFA and FT fuel). What are the potential benefits of alternative jet fuels with respect to local air quality? Another potential benefit of using alternative jet fuels is the reduction in emissions that affect local air quality, in particular SOx and PM. These emissions can lead to respiratory diseases such as asthma, and they are major contributors to acid rain, smog, and reduced visibility. Salicornia to HEFA and FT Algae oil to HEFA Jatropha oil to HEFA Rapeseed oil to HEFA Palm oils to HEFA Soy oil to HEFA Coal and Biomass (w/ CCS) Switchgrass to FT fuel Coal to FT fuel (no CCS) Natural gas to FT fuel Oil shale to jet fuel Oil sands to jet fuel Crude to ULS jet fuel Crude to conventional jet fuel 0 1 2 3 4 5 6 7 8 9 Figure 2. Relative life-cycle GHG emissions of several pathways for alternative jet fuels (conventional jet fuel = 1.0; adapted from Stratton, Wong, and Hileman 2010).