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Alternative Fuels for the Military, but only if the Price Is Right

As a means of ensuring long-term fuel supply security, the U.S. military is actively pursuing development of petroleum-alternative jet fuels from domestic resources. In addition to being “drop-in-compatible” with and less carbon-intensive than their petroleum-derived counterparts, they must be cost-competitive.

The U.S. Congress has been debating over whether to allow funding for production of renewable biofuels for use by the military. Last year, the U.S. Navy spent approximately $26 per gallon to acquire renewably derived jet fuel for testing by jet aircraft. While it can probably be agreed that $26 per gallon is unsustainable, “first-off” technologies are almost always considerably more expensive than their proverbial “nth plant” versions, which benefit from process optimization, engineering, and manufacturing improvements generated as commercialization progresses and market penetration increases.

Recently, the Energy & Environmental Research Center (EERC) at the University of North Dakota produced a specification-compliant jet fuel by combining blendstocks made from coal and biomass. The EERC has already developed a technology to produce 100% renewable jet fuel from vegetable oil, but a better near-term solution may be an approach that combines fossil and renewable resources.

Production of the coal blendstock utilized an Accelergy Corporation microcatalytic direct coal liquefaction (DCL) technology to convert coal to raw liquids, which were then upgraded via hydroprocessing. Because DCL leverages the fuel chemistry of coal, DCL liquids typically require less hydrogen consumption and are less carbon-intensive than other coal-derived liquids that require more extensive processing. The biomass blendstock was a 100% renewable jet fuel product made from canola oil using the EERC’s integrated hydrotreating and isomerization technology. The fuel produced from these blendstocks was evaluated by the U.S. Air Force Research Laboratory (AFRL) at Wright–Patterson Air Force Base and found to comply with AFRL alternative jet fuel preliminary screening criteria.

In addition to energy density, freeze point, and flash point, another critical performance parameter for synthetic (as well as petroleum-derived) jet fuel is thermal stability. By exceeding the thermal stability standard for U.S. military jet fuel, the coal–biomass-derived fuel was demonstrated to burn cleanly, which means it will not leave performance- and safety-degrading deposits on important turbine engine parts.

The new fuel is part of a long-term EERC effort to broaden the resource base for fuel production beyond petroleum in alignment with the military need for energy security. Enhanced operability, energy security, and reducing aviation’s impact on the environment are drivers toward the use of renewable and nonpetroleum sources for producing jet fuel.

New technologies such as coal–biomass liquefaction reduce the environmental footprint of the fuel, limit land use competition between food and fuel production, and draw on the vast coal reserves in the United States. Such fuel processing allows the United States to continue to tap existing infrastructure while integrating a greenhouse gas-neutral biomass feedstock.

In summary, an advanced direct liquefaction process shows promise for producing alternative fuels. Liquefaction-derived fuel comprises essentially the same chemical composition as petroleum fuels and integrates well with all aspects of petroleum fuel utilization, including production, distribution, storage, and combustion in ground, aerial, and marine vehicles. With the technology showing great viability, work continues to lower the cost well below $26 per gallon.

By Chris J. Zygarlicke, Deputy Associate Director for Research, Energy & Environmental Research Center (EERC)