In our previous insight article, we examined various Sustainable Aviation Fuels (SAF) and the role that federal and state incentives play in enhancing their financial viability. Many of these incentives increase when the SAFs offset more conventional emissions. While these processes yield significant emissions reductions, several subprocesses within the SAF supply chain still depend on fossil fuels. In this insight, we use Sesame to quickly identify and evaluate opportunities for further decarbonization within a specific SAF pathway.

The Pathway: HEFA

Hydroprocessed Ethers and Fatty Acids (HEFA) remains the most commercially established  option for sustainable aviation fuel (SAF), according to NREL’s Sustainable Aviation Fuel State-of-Industry Report. In this analysis, we examine a HEFA plant built in Washington state, where some of the strongest per-gallon incentives for SAF are currently available. The HEFA pathway starts with high-oil crops, such as soybeans, corn, or jatropha. These feedstocks are harvested (typically using diesel machinery), dried, and processed into bio-oil. From there, the bio-oil undergoes the HEFA process, requiring additional hydrogen and process heat. After hydroprocessing, the fuel is ready for blending. As shown in Figure 1, US average HEFA SAF creates 30.4 g per MJ of fuel. For scale, traditional jet fuel produces 83.5 g per MJ.

Figure 1: Breakdown of cradle-to-grave jet fuel emissions for the HEFA production pathway. HEFA necessitates a significant amount of process heat, typically supplied by natural gas (NG).

 

Decarbonizing Further
While this is already a significant upgrade from traditional jet fuel’s cradle-to-grave emissions, within this production pathway are opportunities to further reduce emissions of HEFA fuel and increase economic incentives:

• Substitute diesel-powered farming equipment with electric alternatives

• Decarbonize the process heat used in both oil refinement and HEFA

• Use solar energy for the electricity needs of oil refinement and HEFA

• Implement green hydrogen in HEFA instead of blue hydrogen

• Capture carbon from HEFA vents

By implementing all of these solutions, HEFA can achieve a 93% reduction in emissions compared to the traditional 69% reduction (as seen in Figure 2).

Figure 2: Decarbonization opportunities present in the HEFA production pathway. The remaining emissions are from Indirect Land Use Change (ILUC) considerations.

While numerous opportunities for decarbonization exist, some options come with prohibitive costs. We will examine the changes that can be made at the fuel production plant in greater detail. The following sections explore the trade-off between cost and emissions, using current Washington and federal financial incentives as the deciding factor. Sesame’s software platform simplifies the investigation of costs and emissions associated with these alternatives.

The results from this investigation are present in Table 1. Costs are represented as minimum selling price (MSP), which is similar to the levelized cost of product SAF. We’ll break down each case individually below. 

 

Green Hydrogen

The HEFA process requires hydrogen for hydrotreating the resulting fuel. In the base case, it is assumed that this is Blue Hydrogen: hydrogen produced from natural gas, which has had a significant portion of emissions captured during the production process (2.6 grams of emissions per megajoule). Green Hydrogen, primarily synthesized through electrolysis, can provide hydrogen with nearly zero upstream emissions.

With the IRA’s $3 credit for Green Hydrogen, the feedstock change results in an increase in price of $1.44 per gallon for a reduction of up to 2.6 grams of emissions per megajoule. When considering Washington’s incentive for percentages of emissions reduction, green hydrogen costs $1.29 more per gallon. If green hydrogen is produced locally through owned wind turbines and electrolysis, the price with incentives is still approximately 22 cents more per gallon.

 

Decarbonize Process Heat

The largest share of process emissions comes from process heat requirements. Washington’s electricity is dominated by hydroelectric production, meaning grid electricity in WA is heavily decarbonized. An electric boiler powered by Washington’s grid electricity costs 28 cents more per gallon than using natural gas, while netting 45 extra cents in incentives. In reducing emissions by almost 7.1 g CO2e per MJ, current incentives means it also costs 18 cents less a gallon to produce.

Implementing carbon capture is also a viable and profitable option. A traditional natural gas process heater with carbon capture reduces process heat emissions by nearly 90%, or 7.75 g CO2e per MJ of fuel. In this case, the MSP is only 16 cents higher than that of the standard HEFA case, but it benefits from over 46 cents more in state and federal incentives. The result is clear: Decarbonizing HEFA’s process heat, whether by grid electricity or carbon capture, could save a HEFA plant up to 29 cents a gallon with Washington’s current incentive structure.

 

Solar for HEFA Process Electricity

The HEFA process doesn’t require much electricity to operate, but it still contributes about half a gram of emissions per MJ of product SAF. A small solar array with a battery could provide a modest benefit to SAF-producing facilities, along with other on-site loads (such as offices). With Washington’s solar capacity, it costs just 2 cents more per gallon to use solar electricity. After incentives, it’s nearly break even. Considering federal tax incentives for installing solar and the potential for lower capital costs in the future, solar could also lead to net savings for a HEFA plant.

Table 1: Decarbonization options for the HEFA production process. Listed is the minimum selling price (MSP) before factoring in credit, along with the MSP after considering federal and state credits.

 

Why Context Matters

Carbon capture has proven to be advantageous for Washington-based HEFA plants. However, not every state offers the same incentives. Nevada, for instance, lacks per-gallon SAF credits, but the state government has invested in SAF production initiatives. Nevada has significantly more readily available solar energy, meaning options that aren’t feasible in Washington or Minnesota could potentially be utilized there. As emphasized in our previous insight, one size does not fit all for SAF, and tools like Sesame allow HEFA projects to identify where decarbonization can enhance project profitability.

 

All results obtained above were generated via Sesame’s software platform. Discover how Sesame Sustainability can transform your emissions and cost modeling processes! Contact us today to learn how Sesame can be leveraged to fit your unique needs. To learn more, visit Sesame Sustainability.