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APPENDIX D Production Technologies for Alternative Jet Fuels While different technologies exist for the production of alternative fuels, the primary differences are the pathways used to convert materials to fuels. For alternative jet fuels, current technology pathways include (a) hydrotreatment of vegetable oils and/or animal fat to produce bio-synthetic paraffinic kerosene (bio-SPK) (also known as hydroprocessed esters and fatty acids), and (b) FT synthesis of biomass and/or coal and natural gas to produce SPK (see Figure 9). Esterification of vegetable oil or animal fat can be used to produce biodiesel (also known as fatty acid methyl ester, or FAME), but the process is not suitable for alternative jet fuels. Other promising pathways include fermentation, lingo-cellulosic conversion, and pyrolysis of biomass. In terms of processing technologies, this report focuses on FT and HEFA processes because they are the most advanced and have the highest likelihood of becoming commercially available in the short term. For example, aviation alternative fuels using the FT and HEFA processes have already been certified. In addition, several FT and HEFA projects have been proposed and are in devel- opment (see Appendix K). D.1 Fischer-Tropsch One process for producing alternative fuels of all kinds, not just jet fuel, is the Fischer-Tropsch process. The FT process uses a chemical reaction to transform a carbon-rich feedstock, such as coal, natural gas, or biomass, into a hydrocarbon fuel. There are variations of the FT process, depending on the feedstock. If the feedstock is coal, the process is known as "coal-to-liquid" or CTL. If the feed- stock is natural gas, the process is called "gas-to-liquid," or GTL. If the feedstock is biomass, the process is called "biomass-to-liquid," or BTL. Some FT facilities use a variation of the FT process, operating a biomass-and-gas-to-liquid (BGTL) or coal-and-biomass-to-liquid (CBTL) process. The typical product distribution of FT production runs is approximately 30% gasoline, 40% jet fuel, 16% diesel, and 14% fuel oil (IATA 2009). Jet fuel produced via this process is often referred to as synthetic paraffinic kerosene. If a higher proportion of concentration of a specific product is desired, such as jet fuel, further processing is required, but it would increase the pro- cessing cost and reduce the overall yield of the plant (Hileman et al. 2009). Carbon capture and sequestration involves capturing the gaseous CO2 released during a produc- tion process and capturing it through storage or by converting it into other carbon compounds that are not released into the atmosphere. 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 atmos- phere. Research is being conducted in finding more efficient means of capture, storage, and con- version (Herzog and Golomb 2004). These include algal systems that could potentially convert the gaseous carbon dioxide into carbon-based compounds and carbon-based oils through photo- synthetic activity. Other alternatives for CO2 storage include depleted oil and gas reservoirs and 84
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Production Technologies for Alternative Jet Fuels 85 Bio-derived feedstocks Fossil fuel feedstocks Vegetable oil/ Coal/natural gas Biomass animal fat Hydro- Esterifi- Fischer-Tropsch treatment cation synthesis Biodiesel Bio-SPK (FAME) SPK (HEFA) Figure 9. Current technology pathways for the production of alternative fuels. Adapted from Altman (2010). unminable coal seams. However, available technologies are still very expensive, and the regula- tory regime around CCS has not been fully developed. More information on CCS can be obtained from "Carbon Capture and Sequestration Technologies" (MIT 2011) and Technologies: Carbon Sequestration (NETL 2011). D.2 Hydroprocessed Esters and Fatty Acids HEFA is refined from plant oils (see Figure 10). During the HEFA process, raw oils react with hydrogen (hydrotreatment step), producing the by-products water and carbon dioxide. These by-products remove excess oxygen from the raw oils. Next, the deoxygenated oils again react with hydrogen to undergo hydrocracking--breaking long hydrocarbon chains into smaller ones. During the product separation stage, fuels are extracted by grade. In a typical refining run, the yield for jet fuel is about 10% of the overall output (Bauen et al. 2009). With selective cracking, the yield for jet fuel rises to 50% to 70% of the overall output, but with the same losses in yield and cost performance as with FT. D.3 Main Characteristics of the Fischer-Tropsch and HEFA Processes Table 17 lists the main characteristics of the FT and HEFA processes. A key conclusion from the comparison of HEFA and FT technologies is that FT is suited for large-scale operations in which a large number of products, particularly large quantities of gases and heavy liquids, can be managed in an advantageous manner. This large-scale operation also Hydrogen Bio-derived Jet fuel, diesel oil Deoxygenation Selective Hydrocracking/ Product Separation Isomerization Water, CO2 Figure 10. Notional diagram of the HEFA process. Adapted from Anumakonda (2010).
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86 Guidelines for Integrating Alternative Jet Fuel into the Airport Setting Table 17. Characteristics of the FT and HEFA processes. Characteristic Fischer-Tropsch SPK (FT SPK) Hydroprocessed Renewable Jet (HEFA or bio-SPK) Feedstock Biomass, coal, natural gas. Plant oils or animal fats. Cost of feedstock Very low for biomass. High for commercial plant oils Low for coal. (e.g., soybean) because of Medium for natural gas. high demand. High for plant oils not currently produced at commercial scales (e.g., Camelina) but expected to decrease as scale is achieved. Medium to low for animal fats. Cost of feedstock High infrastructure and Medium to high for extracting gathering and logistics procurement costs for biomass plant oils, but low for collection and transport. transporting plant oils with Low for natural gas. existing infrastructure. Medium for coal. Medium to high for animal fats. Production costs Low marginal cost of production. Low to medium marginal cost of production. Scale Very large (300 million GPY Medium (7.5 million GPY minimum, 3 billion GPY typical). minimum, 90150 million GPY typical). Product quality High (meets critical jet fuel High (meets critical jet fuel properties--like freeze and flash properties--like freeze and points--defined in the ASTM flash points--defined in the specification). ASTM specification). By-products Large quantities (60%80%) of by- Moderate quantities (~20% products: diesel, high molecular 30%) of renewable diesel, LPG waxes, lights, naphtha, LPG. and naphtha. Capital requirements FT plants are very large--larger Depends on scale. Smallest than typical crude oil refineries. practical scale is about 7.5 Small-scale FT plants are being million GPY for about $50 proposed, but typical capital million; larger scale of 70 investments are about $500 million million GPY for about $250 for small scale (75 million GPY) million. and running up to billions of dollars for large scale (750 million GPY). Plant area or physical Typical refinery size footprint is 10 Large-scale refinery is about footprint to 15 acres. one-tenth the size of a standard refinery--roughly 1 to 2 acres. Life-cycle GHG footprint Very large for coal gasification Low for land-based plant oils without CCS. ignoring land use. Medium for natural gas. Very low for sea-based plant Low for biomass ignoring land-use oils (e.g., algae). change. Medium for plant oils including Medium for biomass including land-use change. land-use change. necessitates adequate supply of large quantities of feedstock, achievable either by a robust feed delivery infrastructure or a concentrated source of feedstock. This is the reason that FT technol- ogy has been successful when coal or natural gas has been used as the feedstock, with FT plant sites co-located with or in proximity of large coal mining operations or oil and gas drilling oper- ations. The scattered and distributed nature of biomass availability makes it a challenging prob- lem for BTL plants. Co-feeding some amount of biomass along with coal for CBTL plants is sometimes a partial solution of this problem. Key challenges for HEFA technology are the restricted supply of plant oils and the resulting high price of these oils for alternative jet fuel production; however, as production of plant oils increases and the supply chains of these feedstocks strengthen, the potential exists for HEFA pro- duction to become commercially viable. Incentives and long-term supply contracts may be required to help this industry get started and grow. With time, as the supply chains for bio-
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Production Technologies for Alternative Jet Fuels 87 Bio-derived feedstocks Fossil fuel feedstocks Vegetable oil/ Coal/natural gas Biomass animal fat Hydro- Esterifi- Cellulose Fermentation/ Pyrolysis/ Fischer-Tropsch treatment cation conversion hydrolysis liquefaction synthesis Biodiesel Ethanol/ Bio-SPK (FAME) Bio-SPK alcohols SPK SPK (CRJ) (FRJ) (PRJ) SPK (HEFA) Future technology pathways Figure 11. Current and future technology pathways for the production of alternative fuels. Adapted from Altman (2010). derived feedstocks, including plant oils, biomass, and agricultural residue evolve, it is also con- ceivable that BTL and CBTL technology may also become economically viable at scale. D.4 Other Refining Technologies Other candidate technologies for producing aviation alternative fuels or bio-SPK include cel- lulosic conversion, fermentation, and pyrolysis. These pathways are currently known as catalytic renewable jet, fermentation renewable jet, and pyrolysis renewable jet, respectively (see Figure 11). These processes produce jet fuel from sugars obtained directly from cane, sorghum, or other sugar-producing feedstocks, or indirectly by extraction from cellulosic feedstocks. These processes are still in the development phase and no short-term commercialization is expected; however, these pathways have the potential to one day offer other options for alternative fuel production. More information about these processes is available from the National Advanced Biofuels Con- sortium (NABC 2010) and the Advanced Biofuels Association (ABFA 2011). ABFA and its mem- bers work closely with CAAFI and its sponsors to align policy and technical matters.