Bio-Digest: Sustainable aviation fuel with integrated carbon capture and storage
The Bio-Digest series brings you the latest in biomass and bioenergy research, presented in easy-to-digest summaries, to keep you informed about the rapidly evolving bioenergy landscape.
Reducing the environmental impact of international aviation through sustainable aviation fuel with integrated carbon capture and storage
Alberto Almena (University of Salamanca), Regina Siu (formerly Aston University), Katie Chong (Aston University), Patricia Thornley (Aston University), and Mirjam Röder (Aston University)
Without intervention, international aviation is projected to become the second-largest source of global greenhouse gas (GHG) emissions by 2050. Sustainable aviation fuels (SAF) are the only short-term mitigation strategy for a sector still heavily dependent on fossil fuels. SAFs include fuels produced from biomass, and synthetic fuels (e-fuels).
Global market-based measures such as CORSIA (Carbon Offsetting and Reduction Scheme for International Aviation) aim to support the aviation industry in reducing emissions and encourage the deployment of SAF. The CORSIA framework assigns emission values to certified SAF production routes, thus allowing airlines to claim emissions reduction bonuses when they use those fuels. The CORSIA approach to calculating emissions only considers fossil carbon. Biogenic carbon flows are excluded because it is assumed that they are climate neutral (ie, the amount of biogenic carbon emitted is equal to that sequestered during biomass growth).
Future biomass-to-SAF production could be integrated with carbon capture and storage (CCS) to support greater emission reductions and potentially net negative emissions (ie, permanent removal of atmospheric carbon). This research evaluated the effect of integrating CCS with a CORSIA-eligible fuel process and aimed to address gaps in biomass-to-SAF emissions assessments. We developed a detailed model of the production of SAF from pine wood, via the Fischer-Tropsch Hydroprocessed Isoparaffinic Kerosene (FT-IPK) pathway with CCS. This model was integrated with a comprehensive lifecycle assessment (LCA), carried out using a well-to-wake approach.
Key learnings
- Biomass-to-SAF production with CCS can offer significant emission reductions compared to conventional jet fuel
LCA of SAF produced with CCS indicated a 74% reduction in fossil GHG emissions compared to conventional jet fuel, when biogenic emissions are assumed to be carbon neutral. This figure is comparable to the 50-90% range reported by synthetic e-fuel pathways, but the energy demand was two orders of magnitude lower.
- Credible evaluation of the environmental performance of biomass-dervied SAF requires consideration of biogenic and fossil carbon dynamics
By excluding biogenic carbon flows from emissions calculations, the CORSIA approach overlooks the impact of other biogenic emissions and excludes the negative carbon flow created from the atmosphere into geological storage when CCS technology is incorporated into the biomass-to-SAF conversion process.
- Flying with net negative emissions is possible if engines operate on 100% SAF
Current certifications would see engines run on a 50:50 blend of SAF with conventional jet fuel rather than on 100% SAF. Considering both fossil and biogenic carbon flows, LCA found that the net carbon balance of a system using this 50:50 blend is 30.5 g CO2e MJ-1. If engines were adapted to run on 100% SAF, this would allow flights with overall net-negative emissions of -20.0 g CO2e MJ-1.
- Transparency is pivotal when claiming for SAF emissions reductions
Our calculated emissions score for FT-IPK SAF was 49% higher than the CORSIA default value, because different process configurations and modelling assumptions have a significant impact on the emissions calculations. Transparency around emissions calculations under the CORSIA framework is therefore essential.
- Feedstock requirements will be a limiting factor for bio-derived SAF
Using all of the UK’s domestic forestry residues for SAF production would meet just 0.7 % of the UK’s aviation fuel demand. Clearly, in the future a mix of low-carbon fuels and solutions, including biofuels, must coexist.
