Production of Sustainable Aviation Fuel from Renewable Feed Sources

Co-authors: Raghu Dronamraju, Principal Process Engineer, Fluor Canada & Jon Isley, Executive Technical Director, Fluor Canada

CO2 emissions from the transportation sector, including end-use sectors, account for approximately 23% of the total CO2 emissions globally. Based on current trends, these are projected to increase by nearly 50% by 2030 and more than 80% by 2050 [1]. Of this, aviation accounted for 2% of global energy-related CO2 emissions in 2022, having grown faster in recent decades than rail, road, and shipping [2]. In late 2022, International Civil Aviation Organization (ICAO) Member States adopted a goal to achieve net zero carbon emissions from international aviation by 2050. The agreement aims to reduce emissions within the sector itself directly from aviation activity, as opposed to via offsetting emissions through purchase of credits. Although it remains non-binding and lacks intermediate goals, member state governments are expected to produce action plans within their own national timeframe and capabilities [3]. In anticipation, and to meet a growing consumer demand, the world’s largest airlines have already taken it upon themselves to use and expand SAF in their current fleet [4][5][6][7].

To meet the target, get emissions on track and achieve Net Zero Emissions (NZE), several technical measures need to be taken such as adopting Sustainable Aviation Fuel (SAF), improvements in design of airframe and engine designs and operational optimization. SAF can reduce carbon dioxide emissions on a lifecycle basis by up to 80% when compared with conventional fossil jet fuel. Increasing the use of these fuels to get in line with the NZE scenario will require a significant ramp-up of investments in production capacity.

The primary SAF production strategies utilize a biological source of hydrocarbon feedstock to produce liquid fuel by processing the feedstock using one of several pathways. The most common feedstocks used today are vegetable oils (used and virgin) and animal fat. Emerging research and development on advanced biofuel technologies is unlocking more abundant and cheaper feedstocks such as agricultural residues, dedicated energy crops and municipal solid waste. Bio sourced feedstocks where carbon dioxide from the atmosphere is converted back to fuel through photosynthesis provides a circular source of hydrocarbon-based energy that achieves a net reduction of net carbon dioxide emissions while at the same time takes advantage of existing agricultural and jet fuel industry infrastructure.

Production of SAF from waste oils and fats and designated virgin oils requires pretreatment steps followed by hydrodeoxygenation and dewaxing. The main constituents in the oil are triglycerides with a glycerol back bone connecting three fatty acids. The hydrodeoxygenation reaction splits the oil into straight chain alkanes and propane. The dewaxing reaction further isomerizes the straight chain alkanes into branched isomers to meet the cold flow properties of transportation fuels.

The catalyst in the dewaxing reactor can be tailored to produce a mix of diesel and SAF by changing the final molecule length as desired. The SAF yield can be maximized by varying the operating conditions to produce SAF and renewable diesel of varying specifications. The consequence of maximization of SAF production is reduced cycle length of the catalyst and lower overall liquid yield with a corresponding increase in renewable gas and naphtha.

Process units designed for production of renewable diesel can be revamped for SAF production as the market requirements between renewable diesel and SAF change. Heat integration is optimized to convert from a diesel production to maximum SAF yield and achieve process efficiency. Fluor’s capabilities in plant design and layout, along with modular execution, allow for revamp and SAF integration into the existing renewable diesel plant. The equipment can be grouped with tie-ins to ensure that the revamp is integrated seamlessly with the rest of the plant.

Other process routes for production of SAF from biomass and other organic waste products includes gasification, hydrothermal liquefaction and pyrolysis. The raw material for gasification is very diverse ranging from agricultural, lignocellulosic, forestry wastes to urban solid waste. The gasification process is followed by Fischer-Tropsch synthesis and hydrocracking. The final hydrocracking step has many similarities in tailoring the final renewable fuel products as discussed above for fats and oils.

Hydrothermal liquefaction of biomass involves reaction with water to generate a higher energy density product with low oxygen content compared to pyrolysis. The process is capable of efficiently processing wet and dry biomass and generating “crude” oil that can be upgraded to liquid fuels including SAF after treatment and hydroprocessing. Hydrothermal liquefaction is still being commercially developed but offers the potential of efficiently converting biomass into the raw hydrocarbons needed for renewable process industries.

Regardless of the technological pathway, conversion of biologically sourced feedstocks into SAF is commercially viable and increasingly needed today to meet a growing consumer demand. The key to successful projects is to have partners that understand this technology landscape and can reliably provide the scope of services and facilities needed to make these projects a reality.

Fluor has been leading the industry in engineering commercial-scale facilities for new technologies. We provide owners and technology developers with expertise in scale-up, site selection, project management, process design, engineering, procurement, construction and start-up. This experience includes integration with existing refineries and utility systems to find synergies and efficiencies with both capital and operations. In the world of SAF, this means –

Maximize process energy efficiency by incorporating heat recovery and cogeneration systems.
Implement water conservation measures.
Practice proper waste management including disposal of solid waste and treatment of wastewater.
Use carbon capture, utilization and storage technologies in conjunction with SAF production facility. Additional credits can be achieved by sequestering carbon from biological sources.
Implement modularization strategies for construction and installation.

Fluor has designed and constructed more than 100 bio-related facilities including both chemical and biological routes from biomass to biofuels and has key experience for more than 25 years.

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