[jws]

Extract CO2 and H2 from seawater, react to form hydrocarbons of varying lengths, then refine. Presumably all powered by the nuclear reactors.

initial studies predict that jet fuel from seawater would cost in the range of $3 to $6 per gallon to produce

[ChuckMcM]

That is exactly why its such a big deal. Current jet fuel costs over $8/gal delivered. It costs so much because even if it comes out of the refinery at San Diego at $2/gal it has to be loaded into an oiler [1] and then driven out to sea where the carrier task group is.

If you're on a nuclear powered aircraft carrier you have plenty of electricity so this is a pretty huge win.

Of course an alternative way to make this feasible for the fleet would be to build a nuclear powered oiler. It could process seawater into jet fuel as it cruised along with the fleet and transfer fuel as needed, but to this day fuel transfer at sea is one of the more dangerous things they do.

[1] http://en.wikipedia.org/wiki/Replenishment_oiler

[jnw2]

http://en.wikipedia.org/wiki/USS_Gerald_R._Ford_(CVN-78) notes that ``Unfortunately the power limitations for the Nimitz class make the installation of the recently developed [Electromagnetic Aircraft Launch System] impossible.'', which seems to indicate that existing nuclear powered aircraft carriers don't always have large amounts of electricity to spare. However, more electricity will be available on future aircraft carriers.

[ChuckMcM]

If you look at the power requirements for the EMALs system you will see why a Nimitz class carrier can't power it. Not only is it a crapload of power, its needed all at once. The JP4 from Seawater project can run at much lower powers and for long periods of time.

[jrabone]

And in fact, here is another illustration of just how hard it is to replace conventional energy storage systems with electricity. High pressure steam stores an enormous amount of energy. EMALs effectively uses 4 flywheels as rotational energy stores, suggesting battery / supercap technology just isn't viable. It does have an efficiency advantage over steam though.

[jnw2]

I bet batteries don't tend to like going from full to empty in the time it takes to launch a plane.

I wouldn't be surprised if later in the Ford class's life, we do see supercapacitors taking over.

[ChuckMcM]

Batteries operate by the principle of ion formation. The chemical process is exothermic with respect to the transfer of electrons from the cathode to the anode. So the more charge that is moved the hotter the batteries get. This is often the limiting factor for charge conversion.

Capacitors on the other hand simply store charge using electrostatic field attraction, the only barrier to their current flow are the i2r heat generated in the conductive paths (a superconducting supercapacitor for example could dump all of its charge instantly without any problems, if such a thing existed, its manufacturer would be worth more than Apple :-)

Flywheels store energy mechanically as angular momentum, they have good energy density, and can return it quickly by being attached to a generator, but are generally hard to deal with in systems with an external acceleration because their tendency to precess if that acceleration results in a rotation that is perpendicular to the flywheel. The proposed carrier ones I've seen are shown as being on gimbals for that reason.

[jrabone]

No, I expect they'd need to be specially designed for it, with a number of compromises (gas venting/replenishment) along the way.

Battery technologies tend to have a limiting internal resistance that determines the maximum discharge rate, although in many cases the maximum SAFE discharge rate is much lower - traditional lead acid will allow you draw so much current that the plates buckle and the acid boils...

It's all down to the chemistry, and every technology has different characteristics and weaknesses - for example, any secondary cell involving nickel or zinc has to deal with the tendency of these metals to grow dendrites when plating out of solution (ie. the recharge case) - this is what bursts a regular AA cell if you try to recharge it using DC. There are simple workarounds, and although the regular dry cell design is not optimal for recharging it can be done. It also causes the memory effect in NiCd cells, and explains why they can sometimes be recovered with a large pulse of charging current (local melting of the dendrites).

[jnw2]

http://en.wikipedia.org/wiki/A1B_reactor indicates that there's 300 MW per reactor on the Ford class, and two reactors, so maybe 600 MW total, although I'm not sure if that's the output of the steam powered electrical generators, or if it's the theoretical amount of energy in the steam coming out of the reactor.

http://en.wikipedia.org/wiki/Miles_per_gallon_gasoline_equiv... says the EPA figures 33.7 kwH is the same as a gallon of gasoline, and there's enough slop in estimating how much power a carrier will have left over for making jet fuel that the error in pretending that jet fuel is the same amount of energy per gallon as gasoline is probably noise.

Other commenters are saying that synthetic fuel is going to take 2-4 times as much energy as the synthetic fuel stores, so let's assume roughly 100 kwH to make a gallon of jet fuel.

That suggests that 600 MW total power might be able to make as much as 6000 gallons per hour if people are happy to leave the carrier drifting with no lights and all its defensive equipment turned off. If the carrier is carrying 75+ planes, that suggests it can make less than 100 gallons an hour per plane. The Google Search summary of http://www.google.com/url?q=http://wiki.answers.com/Q/What_i... says a Gulfstream III consumes 568 gallons per hour. A supersonic fighter jet probably consumes somewhat more, and that leaves me wondering if a Ford class reactor is going to be able to produce enough jet fuel for an active fleet of fighter jets. Certainly, the planes don't fly 24 hours a day, but this estimate suggests that the carrier's reactors might not even have enough left over power to make enough jet fuel to have the average plane on board flying one hour out of 24.

[pdonis]

> 600 MW total, although I'm not sure if that's the output of the steam powered electrical generators, or if it's the theoretical amount of energy in the steam coming out of the reactor

It's the latter. Most of that power goes to moving the ship, not making electricity.

[danmaz74]

But the launch system has to work reliably at any moment, especially when the ship is in full operation at a time of crisis. On the other hand, this process could work at off-peak times, of which I think there is plenty on a carrier too.

[pdonis]

> existing nuclear powered aircraft carriers don't always have large amounts of electricity to spare

The limitation isn't the nuclear reactors, it's the electrical generators, which are only sized to make a small fraction of the total power the reactors are capable of. Most of the reactor power is for moving the ship, not making electricity.

[Gravityloss]

We can look at it this way too: assume an oiler has maybe 10,000 t of oil and takes ten days to travel: 1E7 kg with energy density of 1E7 J/kg, in 1E6 seconds means an average power supplied by one oiler to be in the order of 100 megawatts. Or 10 kg/second. If that synfuel generation rate can be sustained, then the oiler is not needed.

The Nimitz class carriers have two 100 MW reactors: http://en.wikipedia.org/wiki/A4W_reactor

Of course, there's efficiencies, probably the oilers don't always go full speed, there's different distances etc etc...

If we assume 1% efficiency and one dedicated reactor, then we get 0.1 kg/second, 8 tons per day. You could load about two Hornets' internal fuel tanks with that.

In the sea you could probably also try other things than nuclear reactors, like farm algae and harvest it to produce biofuels (biofuel has already been tested in a B-52), or put solar or wind plants out in the ocean where there's space. No energy storage problems if the fuel is generated in situ.

[Mvandenbergh]

Given the refining steps you'd need after making the hydrocarbon feedstock and the dangers inherent in that process, I'm sure that they'd do this on a separate ship.

[001sky]

An alternative way to make this feasible for the fleet would be to build a nuclear powered oiler

--Interesting Idea, depending on the incremental weight, complexity and volatility of the Carrier system.

[Sukotto]

That's a great deal.

Jet Fuel (Kerosene) closed at $3.135/gallon today[1]. And that doesn't include the cost of transporting it from the Gulf Coast to where your Navy needs it.

[1] Sep 28, 2012: http://www.eia.gov/dnav/pet/pet_pri_spt_s1_d.htm

[ChuckMcM]

To be fair you have to subtract off Federal taxes which the government doesn't pay for the fuel it buys which brings it down closer to $2/gal.

[dalke]

That quoted price was the spot price. It doesn't include Federal or other taxes.

Let's suppose that it did include taxes. Federal tax for jet fuel for non-commercial-aviation use is 21.9¢/gal so even if the quoted price of $3.135/gal included federal tax, the without-tax price would still be $2.916/gal, which is a lot closer to $3/gal than $2/gal.

(Gas for commercial aviation use is also subject to the federal transportation tax and harder for me to figure out.)

[fpp]

A bit of history on the work of the NRL on modified Fischer-Tropsch processes / Hydrogenation:

From Wikipedia on Fischer-Tropsch: ( http://en.wikipedia.org/wiki/Fischer–Tropsch_process )

Carbon dioxide reuse

In 2009, chemists working for the U.S. Navy investigated a modified Fischer–Tropsch process for generating fuels. When hydrogen was combined with the carbon dioxide over a cobalt-based catalyst, the reaction produced mostly methane gas. However, the use of an iron-based catalyst reduced methane production to 30 per cent with the rest being predominantly short-chain, unsaturated hydrocarbons [27] The introduction of ceria to the catalyst's support, functioning as a reverse water gas shift catalyst, furthermore increased the yield of the reaction. [28]. The short chain hydrocarbons were successfully upgraded to liquid fuels over solid acid catalysts, such as zeolites.

[A patent application and a more in-detail research paper describing the process(es) is referenced there.]

Overall this looks very interesting as a military application (independence from other sources, logistics).

You will find more articles from 2009+ on this topic by searching for "Fischer-Tropsch seawater".