Renewable fuels play a prominent role in today’s challenging task of emission reduction and independency from conventional fuels in all energy sectors. In order to meet the IATA (International Air Transport Association) emission reduction target of a cut of 50 % in aviation CO~2~ emissions by 2050 compared to 2005, significant efforts concerning alternative fuel synthesis and utilization have to be undertaken. Sustainable aviation fuels (SAF) were introduced into commercial aviation in 2008 and by 2019 more than 180,000 commercial passenger flights with blends using up to 50% SAF have been performed. Within this field, Fischer-Tropsch-Synthesis (FTS) is one of currently four pathways that can produce drop-in SAFs in form of paraffinic hydrocarbons.

Already in 1999, Sasol’s Semi Synthetic Jet Fuel (SSJF) made from coal and natural gas was applied as a 50 % blending component at Johannesburg Airport, demonstrating the feasibility of FT blending fuels early on. These industrial-scale FT plants however display disadvantages by on applying coal as a fossil feedstock and not being load flexible. In this regard, the compact container-scale PtL plant concept as developed by Ineratec GmbH offers a sophisticated and ecologically beneficial approach. In this decentralized Power-to-Liquid approach, syngas is obtained by reverse water-gas-shift reaction of CO~2~ and H~2~. CO~2~ can also be produced directly via “direct air capture” (DAC) which has been demonstrated for various prototypes, e.g. within the German nationally funded project Kopernikus. Therefore Fischer-Tropsch-synthesis has the potential of utilizing surplus energy but also low-cost renewable energy from sources worldwide more efficiently, while also being almost CO~2~ neutral (closed CO~2~ cycle) within the process at the same time. The herein regarded units of Ineratec consist of synthesis gas production from CO~2~and H~2~O via RWGS, Fischer-Tropsch synthesis for the production of long chain hydrocarbons and can be connected to direct air capture unit for CO~2~ production and electrolysis. Besides using renewable feedstocks, the compact FT plants offer the benefits of energy efficient recycling of offgas, a flexible process performance in the minute range and optimized heat removal. Furthermore, on-site Fischer-Tropsch plants present fuel independency and a minimization of ecological and economic factors. This is attractive since aviation and airports experience increasing pressure to introduce renewable solutions not only at small but also at large airports.

The combustion properties of non-hydrotreated Fischer-Tropsch fuels produced in container scale PtL plants have been regarded for their suitability for aviation purposes before, demonstrating their short ignition delay time, high heating value and significantly lower sooting tendency. However, these crude FT products display a high content of olefins, which might cause problems concerning temperature- and storage stability. Therefore in iterative steps, using GCxGC chromatography to determine the chemical composition and by investigating selected “fit for purpose” chemophysical properties for aviation, hydrotreatment and distillation were adapted and optimized as post-processing steps to the compact plant to obtain a FT fuel that would meet the ASTM D7566 criteria. For the postprocessed FT fuel blending analysis was performed utilizing data from the CRC world fuel survey to evaluate the range of blending ratios of the FT fuel with conventional jet fuels determined by identified limiting factors.


Potential of Decentralized Container-Scale PtL Plants for Aviation: From Crude to Post-Processed FT-SPK

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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