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30 6.1 Available Data for Estimating Emissions As noted throughout the report, the research team has encountered some data limitations. The emissions data used for the development of the handbook come from ongoing research projects; it is not certification data. As such, the results of this project are also of a research nature, and the result- ing estimated emission factors will have an associated level of uncertainty. Once the fuels are available, then certification measurements will be made and the resultant emission factors should have increased certainty. The emissions scaling relationships that form the foun- dation of the emissions portion of this work will need to be reconsidered as additional data become available. Given the current lack of data, determining an appropriate methodol- ogy for scaling emissions is difficult, but not impossible, for both diesel engine and jet engine combustion. This stems from the relative lack of scientific understanding of how these emissions are formed during the combustion process (from any fuel, conventional or alternative); this is especially true for the formation of primary PM. For jet engine combustion, this lack of scientific knowledge is being addressed through detailed measurement campaigns of both conventional jet fuel and alternative jet fuels. As an example, considerable aircraft engine emissions data was acquired by the AAFEX research team, which became public at the January 2010 AIAA Aero- space Sciences Meeting. This includes data for all of the species considered here. Based on unpublished results from this study, it appears that consistent trends are starting to emerge. As noted in Section 3.2, these data should be used to augment or replace the preliminary scaling factors in this report. How- ever, primary PM production from diesel engine combustion is less well understood than jet engine combustion due to the additional factors that affect diesel combustion, such as cetane number. Because of these factors, there will be a limit to the accuracy of these estimates. The key to all of this is to use the best data available at the time of conducting an air- port analysis to modify the relationships herein. As noted in Chapter 5, changes in infrastructure costs due to alternative fuel use are marginal and could bring consider- able variation to the results. Fuel prices are influenced by mar- ket values and are prone to speculation that may not have any reasonable foundation. 6.2 Maturity of Alternative Fuels for Aviation There will be delays before alternative jet fuels will be avail- able for widespread use. This delay is the result of the funda- mental steps that are required to bring an alternative fuel to market. These include: ⢠The feedstock to create the fuel needs to be created in large quantities. (A large airport consumes â¼25,000 barrels per day of fuel, and the nation consumes 1.6 million barrels of jet fuel per day.) ⢠Processing facilities must be built to convert the feedstock into the final certified fuel. Multiple feedstocks are available for the production of SPK fuels. On a worldwide basis, natural gas that is stranded far from populations is available for F-T synthesis into an SPK fuel; in the United States, available natural gas resources are used for heating and electricity generation since these are more profitable. For SPK fuels created by the liquefaction of coal via F-T synthesis, a limitation exists in the lack of a sys- tem for carbon capture and sequestration that would support a widespread coal-to-liquids industry. Biomass could also be used to create an SPK fuel either by F-T synthesis or via hydro- treatment; however, the existing agricultural infrastructure is designed for the harvest of food crops, and the ability to har- vest large quantities of high-energy biomass that does not off- set food production is currently limited. Some testing is now C H A P T E R 6 Issues and Challenges
31 underway for growing fuel crops in rotation with food crops, such as growing Camelinabetween wheat crops when the fields would otherwise lie fallow. Also, there is considerable promise since multiple crops (e.g., Jatropha, halophytes, and algae) could yield large quantities of renewable oil on marginal land that is not otherwise suitable for agriculture. The construction of facilities to process these fuels will require considerable investment and time. Some examples merit consideration. The first example is the Oryx plant in Qatar that will convert natural gas to SPK fuels via the F-T process. The construction of the facility required two and a half years (not including the time for planning, permitting, etc.) at a capital cost of $950 million; it will produce roughly 34,000 barrels per day (24,000 of which will be diesel fuel). Such a facility could also be designed to produce a compara- ble amount of jet fuel since diesel and jet fuels have similar refining requirements. The second facility to consider is the Neste plant that is being built in Singapore to hydrotreat veg- etable oils to create an SPK diesel fuel. Scheduled for com- pletion in 2010 and at a cost of $850 million, it will produce roughly 15,000 barrels per day of fuel. These plants both cost nearly a billion dollars and could produce fuel sufficient for a medium- to large-sized airport. Several companies are in the process of planning F-T facili- ties for the conversion of coal to liquids (e.g., Rentech, BAARD Energy, and American Clean Coals Fuels), and the Solena Group has announced plans to develop an F-T facility to cre- ate SPK fuels from municipal waste. All of these facilities could come online early this decade. When completed, these facili- ties would have a combined capacity slightly over 100,000 bar- rels per day, of which some fraction could be available to jet fuel use. As an indication of the movement toward commercial- ization of alternative jet fuels, in December 2009, 12 airlines (Air Canada, American Airlines, Atlas Air, Delta Air Lines, FedEx Express, JetBlue Airways, Lufthansa Airlines, Mexicana Airlines, Polar Air Cargo, United Airlines, and US Airways) signed memoranda of understanding (MOU) with AltAir Fuels, LLC, and Rentech, Inc., to begin purchase negotiations for alternative aviation fuels. Two additional airlines (Alaska Airlines and Hawaiian Airlines) signed an MOU with AltAir fuels, and AirTran signed an MOU with Rentech. Based on these events, it is likely that over the coming decade, alter- native jet fuels will be available in quantities sufficient to meet the needs of a few large airports. 6.3 Implementation Realities The airports surveyed for this project were generally open to the idea of using alternative fuels as long as they met the current or new jet fuel specifications and were drop-in fuels. However, the airports generally take their cues from their ten- ant airlines since jet fuel use for aircraft exceeds the volume of fuel use for GSE by two or three orders of magnitude. While some airports were enthusiastic about the environmental benefits that could be gained by using alternative fuels, practi- cal considerations were also significant. The concerns expressed included: ⢠At airports that do not have fueling consortia, individual air- lines purchase and own their jet fuel, where it is usually com- mingled with other airlinesâ fuel in the fuel storage tanks. ⢠Aircraft fueling and GSE fueling are entirely separate, with different service companies responsible for each. ⢠Unless there were a guarantee that the alternative fuel would always be cheaper than diesel fuel for off-road equipment (considering all costs and subsidies), airports would want to maintain separate fuel storage and handling systems for GSE. None of the concerns expressed by airports are insur- mountable. However, each airport presents a unique set of hurdles that will have to be overcome to gain the benefits of using a single alternative fuel for both aircraft and GSE.
