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Navy Looking Into Ships That Run on Seawater

Forget the environmental pluses, the tactical advantages of such a propulsion system would be mind-blowing for the U.S. Navy.

Last month, a national-security commission advised Congress to fund shipbuilding and increase the U.S. naval presence in the Asia-Pacific region in the next decade to compete with China’s growing fleet. But upping production of petroleum fuel to meet potential future demands is at odds with the Navy’s plans to reduce its dependence on the fossil fuel, the deadlines for which are fast approaching. The Department of the Navy has pledged to cut petroleum use in the service’s commercial fleet in half by 2015, and produce at least 50 percent of its jet fuel using alternative sources by 2020.

The Naval Research Laboratory, a 90-year-old corporate research hub serving the Navy and Marine Corps, is searching for such alternative sources. Led by analytical chemist Heather Willauer, the lab is currently developing technology that sucks up the gases necessary to produce synthetic jet fuel for ships right out of the seawater they tread. If and when it becomes commercially viable, the technology could transform naval operations.

“If they made fuel at sea,” Willauer says, “they wouldn’t be buying it.”

The process begins with a three-chambered cell that receives a stream of seawater in the central compartment. Right now, one of these units sits on the shore of Key West, Fla., at the lab’s Center for Corrosion Science & Engineering facility.

The cell pulls a relatively pure and concentrated source of carbon dioxide from the seawater. This source is usually better than carbon dioxide recovered from flue or stack gases produced by the burning of fossil fuels, Willauer says. Such gases require expensive, energy-intensive hardware to further purify them so they’re safe to use and won’t harm living organisms.

The cell produces hydrogen, which aids in recovering carbon dioxide from seawater. Both processes occur in tandem. The unit captures up to 92 percent of carbon dioxide from the seawater, where it is 140 times higher in concentration than in the air. All the energy supplied to the cell goes into making hydrogen, not into the extraction process, so the recovered carbon dioxide is actually free, Willauer says.

The lab then uses an iron-based catalyst to convert the gases into olefins, a type of reactive chemical compound. The compound can easily undergo further catalytic conversion into a liquid that contains hydrocarbon molecules, which can eventually be transformed into jet fuel.

The entire process costs about $3 to $6 per gallon of jet fuel to produce.  That’s about the current price on the open market.

The current downside, the process chemically creates more carbon in the atmosphere.  Al Gore might be a tad upset about that.

This sounds similar to what NASA wishes to do for a manned mission to Mars.  The first rocket sent to the red planet wouldn’t be the mission capsule, but a fuel station / return ship which would land and turn out rocket fuel by sucking in the Martian atmosphere and chemically converting the needed amount fuel for the return trip to Earth.

Of course, all this is moot if you’re dealing with a nuclear-powered submarine or aircraft carrier.  That’s an entirely different propulsion system.

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  • Unless the laws of thermodynamics have been repealed, this isn’t going to work.