(501e) Implications of Integrating Carbon Capture and Storage Technology into Sustainable Aviation Fuel (SAF) Production

From the early 20th century until today, air traffic has shown a relentless growth in passengers and goods mobilised, only disrupted by the mobility limitations imposed during the COVID-19 pandemic. At present, air travel accounts for 2-3% of global carbon emissions (ca. 800 Mt CO₂ per year). If no action is taken, international aviation is forecasted to become the second-largest emitter by 2050.² The International Air Transport Association (IATA) committed to cap the CO₂ emissions generated by international aviation to 2020 values and halve that output by 2050 by means of sustainable aviation fuels (SAFs). However, their high cost can jeopardize the economic performance of airlines limiting their use.³ To meet emissions mitigation targets and endorse technology development for SAF utilization, global market-based measures like CORSIA have been implemented. Under the CORSIA framework, specific lifecycle emissions values are assigned to a list of certified SAF production routes, allowing airlines to claim for emissions reduction bonuses. Only fossil carbon was evaluated to calculate those values, so potential emission reductions originated from carbon capture and storage technologies (CCS) within any biomass-to-SAF routes are excluded.⁴

The objective of this research was to investigate a CORSIA-eligible fuel process, that is suitable to incorporate carbon capture and storage technology, and compare the life cycle emissions score computed in this study with the one provided by CORSIA. The Fischer-Tropsch Hydroprocessed Isoparaffinic Kerosene (FT-IPK) pathway, an ASTM-certified route to produce jet fuel from waste wood, was the selected process to be evaluated. This study additionally contributed to resolve the lack of comprehensive assessment in determining the carbon balance linked to the production of aviation fuel from biomass.⁵ A complete and detailed model was developed in a validated and robust process simulation software (Aspen Plus) for the FT-SPK route for SAF production from wooden residue, which included feedstock pretreatment (biomass drying and torrefaction), biomass-conversion (entrained flow gasification, syngas conditioning and Fischer Tropsch island), carbon dioxide removal (Selexol process) and CO₂ compression, refining and upgrading stages (fractionation and isomerization), SAF yield maximization processes (oligomerization and wax cracking) and auxiliary unit operations (air separation unit and combined cycle gas turbine). The work examined the underpinning engineering process/steps and integrated a comprehensive lifecycle assessment (LCA) implemented in SimaPro software, with a well-to-wake approach (see Figure 1), were both fossil and biogenic carbon flows were accounted. The LCA enabled the tracking of all impact contributions to the final score of SAF, so the recommendations and conclusions derived from this study are based on rigorous scientific methodology and entail high confidence.

Results showed that, for the operational scale and process described, 145 t kg h^-1 pine wood was required to generate 185.1 MW of liquid FT hydrocarbon fuels. The biomass-to-liquid fuel efficiency was 51 %, calculated on a dry basis (16.95 MJ kg^-1). The CDR unit removed 95% of the CO₂ content from the syngas, allowing to capture 72% of the CO₂ generated during the whole biomass conversion process. The total electricity and heat consumption were 33.4 MWe and 140.5 MWth, respectively. The heat demand could be internally satisfied after performing heat integration due to the highly exothermic nature of biomass gasification and FT synthesis. External power supply was required since just 85 % of the power requirements could be co-generated at the CCGT. Thus, the produced fuel reported an energy intensity of 0.01 MJ/MJ liquid fuel, measuring two orders of magnitude below e-fuel production pathways.^6,7

The well to wake LCA reported 21.6 g of fossil CO₂e per MJ of FT-IPK produced, which indicates a 74% reduction in fossil carbon emissions (Jet A1 scores 81.8g CO₂e MJ^-1), a figure that rivals with the 50-90% reduction range reported by synthetic e-fuel pathways.^6,7 The value obtained is 49% higher than the CORSIA default lifecycle emissions value indicated for this route (8.3 g CO₂e MJ^-1).⁸ Differences on process configurations and computing assumptions where identified, which greatly affects the reported score. On this basis, transparency in the emissions estimation is pivotal when claiming for emissions reductions, to certainly achieve the emission mitigation targeted with this framework. Conversely, present jet turbine engines cannot run on this fuel due to the lack of aromatics content and low density. The ASTM certified a 50:50 mass FT-IPK and Jet A1 blend to operate a commercial aircraft, thus limiting the impact from using SAF, which emits 51.5 fossil CO₂e MJ-1 fuel used by the aircraft. When accounting fossil and biogenic carbon dynamics, i.e. the net CO₂ carbon balance of the system, using the ASTM-certified blend result in a positive CO₂ flow to the atmosphere estimated in 30.5 g CO₂e MJ^{- 1}. Adapting the engines to operate with 100% SAF would, conversely, result in net-negative emissions. A negative carbon flow of -20.0 g CO₂e MJ^-1 from the atmosphere to a geological could be generated. This finding suggests that a better strategy would be adapting the engines to operate this type of fuel, instead of attempting synthetic fuels to replicate the features of the conventional fuel to operate the existing engines.

References

[1] ICAO. Environmental Report Chapter Six - Climate Change Mitigation CORSIA 2019. 2019.

[2] UK Governemnt. Department for Transport. Jet Zero Consultation. 2021.

[3] Watson MJ, Machado P, da Silva AV, Rivera Y, Ribeiro C, Nascimento C, Dowling AW. Sustainable aviation fuel technologies, costs, emissions, policies, and markets: A critical review. Journal of Cleaner Production 2024; 141472. https://doi.org/10.1016/j.jclepro.2024.

[4] ICAO. CORSIA Supporting Document. COSIA Eligible Fuels - Life Cycle Assessment Methodology. 2019.

[5] The Royal Society. Net zero aviation fuels: resource requirements and environmental impacts. 2023.

[6] Liu CM, Sandhu NK, McCoy ST, Bergerson JA. A life cycle assessment of greenhouse gas emissions from direct air capture and Fischer-Tropsch fuel production. Sustain Energy Fuels 2020;4:3129–42. https://doi.org/10.1039/C9SE00479C.

[7] Rojas-Michaga MF, Michailos S, Cardozo E, Akram M, Hughes KJ, Ingham D, et al. Sustainable aviation fuel (SAF) production through power-to-liquid (PtL): a combined techno-economic and life cycle assessment. Energy Convers Manag 2023; 292:117427. https://doi.org/10.1016/j.enconman.2023.117427.

[8] ICAO. CORSIA Default Life Cycle Emissions Values for CORSIA Eligible Fuels. 2021.

[9] Almena A, Siu R, Chong K, Thornley P, Röder M. Reducing the environmental impact of international aviation through sustainable aviation fuel with integrated carbon capture and storage. Energy Conversion and Management 2024;303:118186