Kinks in the pipeline: A survey of downstream alternative jet fuels challenges

We often hear about how biofuels and other alternative fuels will be needed to decarbonize the aviation sector in the long-run. How easy or difficult will this be to achieve? There are already some examples of alternative jet fuel (AJF) use, although it is currently a very short list. On a high level, the challenges facing widespread use of AJF involve two steps between production and when it is pumped into an aircraft wing: blending and transporting. Let’s look at these processes one by one and identify the potential challenges in each.

Blending. Pure AJF has to be blended with conventional jet fuel to be considered a “drop-in fuel”. Most types of AJF that are certified by the standard-setting body ASTM may be blended at levels up to 50% with conventional jet fuel, with the exception of AJF isoparaffins (see table below). The ASTM certification process for HEFA+, among other types, is ongoing. Currently, HEFA+ testing for approval is being performed at 15% blending rate, a much lower rate than most ASTM-approved AJF types.

ASTM-approved AJF production pathways and their maximum blend levels
Pathway Max Blend
Fischer-Tropsch Synthetic Paraffinic Kerosene (FT-SPK) 50%
Hydroproccessed Esters and Fatty Acids Synthetic Paraffinic Kerosene (HEFA-SPK)  50%
Hydroprocessed Fermented Sugar-Synthetic Isoparaffins (HFS-SIP)  10%
Fischer-Tropsch Synthetic Paraffinic Kerosene plus Aromatics (FT-SPK/A)  50%
Alcohol to Jet Synthetic Paraffinic Kerosene (ATJ-SPK) from isobutanol and ethanol 50%

Who blends AJF with conventional fuel, and where? Most biofuel producers do not produce conventional jet fuel, so separate blending units are needed at some point. From a logistical standpoint it may make sense to build a blending facility at airports where AJF and conventional fuels would end up meeting anyways. However, IATA guidelines state that blending has to be done outside of airport premises.

AltAir Fuels, the only AJF producer in the US that operates on a commercial scale, currently mixes and tests their blended, final product at their facility in Paramount, CA. The tests are conducted to ensure that their blended fuel meets drop-in fuel criteria before delivery to the airport. Which takes us to the second logistical step:

Transportation. Currently, under an agreement with United airlines, AJF from AltAir is transported via tanker trucks from their facility to Los Angeles International Airport (LAX)’s fuel farm. Before making regular fuel farm deliveries, AltAir delivered their product directly to United aircraft at the gate via tanker trucks for a two-week trial period. Trial deliveries were requested by other airlines operating from the airport to demonstrate that the fuel was safe to use, before those airlines would accept blended fuel from the fuel farm. This demonstration period, and perhaps other similar “educational efforts” may be required at other airports to encourage widespread AJF use.

In AltAir-United’s case, the airport took a backseat role, which seems to be the norm as airlines take more initiative than airports in buying AJF. However, a few airports have taken the lead in introducing AJF into their operations, including Seattle-Tacoma Airport and Geneva Airport. Seattle-Tacoma Airport has partnered with 13 airlines to work towards to goal to have “10 percent of sustainable jet fuel to be produced locally from sustainable sources within 10 years, increasing to 50 percent by 2050.” In contrast, Geneva Airport is partnering directly with an AJF producer. This type of collaboration is not the first: Oslo airport in Norway was the first airport to directly provide AJF into its fuel farm beginning in January 2016.

The AJF brought to Oslo Airport and LAX Airport is transported via tanker trucks from the AJF producer’s facilities. It’s unlikely that this mode of fuel transport will change anytime soon. Despite having been around for much longer and produced in much higher quantity than AJF, biofuels for road transport are carried the same way, with the addition of rail and barges. Outside Brazil, biofuels are generally not transported in pipelines due to compatibility concerns. It is likely, then, that AJF will be transported this way for the foreseeable future. It may be slightly more expensive than transporting by pipeline, but it definitely works.

So, all in all, there are kinks to straighten out for AJF producers and consumers. But these sound more like pebbles compared to boulders of challenges found in the upstream production of advanced, low-carbon AJF pathways.

Alternative fuels
Aviation Fuels