initial studies predict that jet fuel from seawater would cost in the range of $3 to $6 per gallon to produce
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.
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.
--Interesting Idea, depending on the incremental weight, complexity and volatility of the Carrier system.
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
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".
This is why electric vehicles won't work. I'll copy in most of a comment I made a few days back.
Let's say tomorrow some grad student gets fusion going at a very low price. The best way to use this to power cars would be to use it to create a fuel with a high energy density. If you had 'free energy' you'd extract C02 from the atmosphere and turn it into a hydrocarbon.
For more info look at:
http://en.wikipedia.org/wiki/Energy_density
and this interview with Nobel Prize winning Physicist Robert Laughlin
http://www.econtalk.org/archives/2010/08/laughlin_on_the.htm....
the key quote is: "The ones that are technically trained get it right away: hydrocarbons, which we burned today have the greatest energy density possible of all fuels. Things that have carbon in them. Will people fly airplanes? Usually people say yes for the same reasons. Well, how are you going to make the airplanes fly? Battery. Batteries are pretty heavy. Oh--you can't have airplanes unless you have hydrocarbon fuels. You could in theory do it with hydrogen, but it's highly dangerous, noxious fuel. Quantum-mechanically, we know the energy content of those fuels is optimal. There will never be anything that beats them." A massive breakthrough in energy density for batteries might be possible but it's unlikely. Huge resources have been put into improving batteries and while they have improved it's not been enough to get near the energy density of hydrocarbons.
Electrolysing water to make H2 and extracting CO2 from the environment, and then synthesizing hydrocarbons from them, is extremely energy inefficient.
Sure, theoretically, it can be done, and maybe one day it could even be done efficiently. But Tesla is making battery-electric cars that work today.
The military does not care about efficiency because they have nuclear reactors on their ships and their goal is to not to have to transport liquid fuel.
Tesla's cars are wildly price inefficient because they cost $100K. For 10K you can get a decent car that has 4 times the range. http://en.wikipedia.org/wiki/Tesla_Roadster
How many gallons of fuel can you get for 90K?
They are nice toys for rich people. Perhaps there is a market for that. Good luck to them.
But for mass transit unless you can get the price of the batteries to plummet it just does not work.
I agree that we will need carbon-based fuels for jet engines, but as for cars, the physics and economics are by no means as favorable as you represent.
That is incorrect. If the fusion source is compact, and can produce a lot of instantaneous electrical power, and is quick to throttle up and down, then a "Back to the Future"-style Mr. Fusion would be the best way to power cars.
Energy density isn't the only factor. There's also a question of infrastructure. Electrical distribution has few moving parts, while extracting C02 from the atmosphere to make fuel and distributing the fuel has many more mechanical parts. A fusion plant which could produce 50 kW, weighed 2 tons, and could be installed in the back yard of a home would mean that a house could be off the grid and still have power left over to charge the car, while using intermediate hydrocarbon storage would mean trips to fill the car, or heating oil, or cooking gas.
So while I completely agree that airplanes will not be powered by batteries, I don't think that energy density is the only factor to consider in the economics equation.
There's also safety to consider.
Cars, on the other hand, experience a combination of aerodynamic and powertrain drag and rolling resistance, of which only (mostly?) the rolling resistance depends on mass. The typical coefficient of rolling resistance is about 10x better than the typical L/D ratio for aircraft (if I believe Wikipedia). Hence, road vehicles are 10x less sensitive to energy density than aircraft.
So a statement that electric vehicles won't work is nonsense, without considering how sensitive the different vehicles are to fuel mass.
(*) Technically fossilised solar energy of course.
It is also effectively win-win. If such a thing becomes possible the costs in much of production will cut very drastically and the potential of things now open would be just incredible. So much of expense is due to energy constraints.
Electric engines run at 92% efficiency. Car engines run at ~15%. So energy density need not reach equivalence.
That physicist is wrong too (Nobel prizes don't mean you aren't wrong - it just means people listen to you more) - jet engines on planes require oxygen to work - hence capped at ~10 km altitude with massive drag causing ineffecient travel.
10 years till battery tech reaches complete parity for lowest denominator cars, and 7 years before we start to see hyper sonic electric passenger jets being tested way up in the upper atmosphere (no oxygen needed, go as high and fast as you want - London - LA in a few hours - space views - cheap power).
Gasoline has an energy density of 132 MJ/US gal, or say 1500 MJ on a full small tank. Modern engines hit 30% thermal efficiency, but then there are drive train losses etc, so I'll give you the 15% as an absolute worst case, AND give you a 100% efficient electric motor / drive train. Therefore your car needs to provide 225 MJ of stored energy for parity.
The best commercially-available Li-ion battery has an energy density of around 245 Wh/kg, or ~ 880 kJ/kg. Therefore you need at least 255kg of conventional batteries for motive energy parity (ie. not counting heat/AC/light etc.). The equivalent in gasoline (0.77 kg/l), weighs 35 kg.
You are asking for nearly a ten-fold increase in usable energy density in battery technology in ten years, at price-parity with gasoline, and with the charging infrastructure to support it. I don't think it's going to happen - assuming lithium-air batteries ARE commercialised on that time scale, the cost of charging that kind of energy in reasonable time, safely, is going to be the real problem here. Every gas station is going to need its own nuclear power plant!
Personally, I read about similar methods, for synthesizing carbon based fuels, many times before. Most of them were private founded but rather small scale. I can't judge if there was a significant science or engineering breakthrough. So, I suspect the only thing that might have changed, is that a clever guy convinced the military this would be a huge strategic advantage.
The ironic thing is, the US could instead focus on producing all their fuel at home to end the dependency on oil from the middle east. Then, they would have an even bigger strategic advantage and wouldn't need as much military investment. Anyway, we might end up with synthetic carbon based fuel with all its advantages - and probably the military can keep their carriers.
Can someone who knows about this stuff comment on whether the energy required to extract the H2 from the water, is more than the energy contained in the chemical bonds of the H2 itself? (assume both sides of the comparison contain equal number of molecules)
I suspect it is.. otherwise they are potentially sitting on a much more important innovation, than mere jet fuel.
2H2 + O2 = 2H2O + energy
The energy is on the right because the reaction is exothermic.
The opposite reaction must be endothermic and must have the same amount of energy on the left:
2H2O + energy = 2H2 + O2
Otherwise, energy isn't conserved.
Because nothing is 100% efficient, there's also energy lost to inefficiencies. So the answer to your question is that yes, you need more energy to make the second reaction happen than is stored in the chemical bond.
I don't get why everyone finds this great since it takes a very long time for carbon in the atmosphere to get trapped in seawater.
CO2 in atmosphere -> CO2 in water -> Ocean acidification[1] -> Change in ocean ecosystem
The oceans absorb OC2 from the atmosphere, which you could argue is good, but it is not without consequences. Putting CO2 in the water moves the problem from having it in the atmosphere elsewhere, but it's still a problem. In some ways then, this can be seen as a good thing, because it is undoing the effects that increased CO2 in the atmosphere has on the oceans. Obviously though, I doubt that its effects would be at all noticeable.
The wiki article already linked has a chapter called 'Possible Impact'.
