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View Diary: Seawater + electricity = jet fuel (15 comments)

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  •  An interesting scenario to be sure, but (5+ / 0-)

    (You knew there was a "but" here somewhere, didn't you?) I feel like I have to raise a couple of points.

    The only way this works out, costwise, is to use existing nukes to produce all the electricity for this process. Electrolysis is a notoriously inefficient means of producing H2 (how does one subscript here?), requiring more energy input than the H2 contains as a fuel. Then add the energy requirements for the other two processes. Net = energy sink.

    Subs have no use for jet fuel, so using their nukes for this purpose would undermine their mission, i.e., staying submerged for long periods. They would have to surface frequently to off-load the jet fuel, simultaneously giving away their position. Not to mention the issue of onboard storage in a confined space. If there are any surface ships besides aircraft carriers that are nuke powered, they would also need onboard storage. Theoretically, other ships in a carrier battle group could help supply their carrier.

    This idea does make sense for nuclear carriers, however. One of the main advantages of a nuke on a carrier is that it makes them less dependent on shore based supplies of fuel in hostile areas. The ability to produce their own jet fuel, which they use in prodigious quantities, would further reduce dependence on shore based supplies. Plus they have plenty of cheap electricity on hand.

    This process has the advantage of being carbon-neutral, but the thorny issues of nuclear power would outwiegh that in most cases. Any island where you could get away with building a nuke would be remote indeed, and would likely not see a lot of air traffic - why not just unload some fuel from a passing carrier, and avoid the cost of the nuke completely?

    While this idea makes a lot of sense from military perspective, it only makes sense for nuclear carriers. If somebody can think of another scenario that might pay off, I'd love to hear about it.

    Sorry about all the nit-picking. I had not heard of this process before your diary, but found it quite interesting. If I'm just talking out my ass, please set me straight. Thanks for posting this.

    Trickle-down theory; the less than elegant metaphor that if one feeds the horse enough oats, some will pass through to the road for the sparrows. - J.K. Galbraith

    by Eric Twocents on Fri Jan 18, 2013 at 05:22:05 PM PST

    •  An extended reply. (5+ / 0-)

      Yup, this costs energy. Pretty much everything does. But the idea is to find net-zero carbon sources for transportation fuel, and this process addresses that.

      The idea is NOT to use existing submarine (or any other ship's) nuclear power plants for this process (because they're already dedicated to moving ships) but rather to use existing Navy expertise in nuclear energy to build a dedicated synfuel manufacturing vessel for the specific purpose of supplying jet fuel to a fleet carrier. Since carrier ops use a large amount of fuel daily, the factory ship could simply make as much as needed and transfer it to the carrier as needed, sharply reducing the amount of fuel storage space needed.

      The island bases considered for this process are Hawaii, Guam, and Diego Garcia, all of which are remote, yet get a lot of air traffic.

      Regarding the "thorny issue" of nuclear power, I would simply point out that it's the safest form of energy ever invented, it emits no carbon, and even in its current, overly-expensive PWR form it is cost competitive with fossil. Fourth gen designs could be cheaper than fossil (see: Robert Hargraves' book Thorium: Energy Cheaper Than Coal), which is the only way the climate crisis will ever be solved.

      Oh, and you subscript using HTML tags <sub> and </sub>.

      We are all in the same boat on a stormy sea, and we owe each other a terrible loyalty. -- G.K. Chesterton

      by Keith Pickering on Fri Jan 18, 2013 at 06:22:07 PM PST

      [ Parent ]

    •   Actually, there are some new avenues for (3+ / 0-)
      Recommended by:
      yuriwho, Lujane, PeterHug

      hydrolysis that are much less energy intensive. As well as new desalinization technologies that  also require very low energy input.

      Information is abundant, wisdom is scarce. The Druid

      by FarWestGirl on Fri Jan 18, 2013 at 08:10:00 PM PST

      [ Parent ]

    •  electrolysis inefficient? (0+ / 0-)

      I wasn't aware of that.  Where are the losses? It seems to me the IR drops would be small compared to the voltage needed to separate H from O.

      •  From what I understand, (1+ / 0-)
        Recommended by:
        Tinfoil Hat

        and I am no chemist, is that hydrogen bonds very easily to other atoms - hence little-to-no free hydrogen in the world.

        The rub is the amount of energy input relative to the amount of energy output. Two H2O (Thank you Mr. Pickering.) split through electrolysis (energy in) yield two H2 and one O2. The reverse is obvious, as is the energy out.

        Energy released through combustion (oxidation) is equal to energy required to reverse the process, or less (not a chemist), so at best you have a 1:1 ratio. If you could derive a ratio of even 0.9:1, input to output, everything around you would currently be powered by low-cost hydrogen.

        To make the cheese more binding, there are inefficiencies in any process, so a theoretical ratio of 1:1 might work out in practice to something more like 1:0.9, or worse. There is no free lunch, or chemical equivalent to a perpetual motion machine. Energy output cannot be greater than energy input.

        You lost me on the "IR drops" business.

        Trickle-down theory; the less than elegant metaphor that if one feeds the horse enough oats, some will pass through to the road for the sparrows. - J.K. Galbraith

        by Eric Twocents on Sat Jan 19, 2013 at 02:31:38 PM PST

        [ Parent ]

        •  thanks for explaining yourself (0+ / 0-)

          As it happens I am an electrical engineer.  The process of breaking the O-H bond itself is close to lossless and almost the same energy is released upon recombining, in combustion or a fuel cell. Efficiencies as high as 96% have been reported experimentally although commercial operations are much less efficient.

          Losses are incurred due to the electrical resistance, "R" encountered by the electrolysis current, "I", on the way to breaking that bond. This causes a voltage drop V = I*R known as "IR drop".  That is where the inefficiency comes in.

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