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I just ran across this thought-provoking eye-popping post on Brave New Climate  by Dr. John Morgan, a chemical engineer.

One thing the ocean has plenty of is hydrogen, which is bound up in water molecules. But did you also know that there is 140 times more carbon in a liter of seawater than in a liter of air? Hydrogen and carbon can be combined chemically to form hydrocarbons, otherwise known as liquid fuels.

So I guess it's no surprise that the US Navy is interested in manufacturing synthetic jet fuel from seawater. What's surprising is that it could be done at a cost comparable to fossil fuel. And that nobody's heard about it yet.

When we burn fossil fuels we release CO2 into the air, but not all of what we release stays there. A large fraction ends up in the sea, because the ocean and atmosphere exchange CO2 freely. In the air, CO2 causes climate change; in the ocean, CO2 forms carbonate and bicarbonate ions, which cause ocean acidification. Both of these are very bad things.

Because there is so much carbon in seawater, it's easier (and cheaper) to remove carbon from the ocean than from the air, and the effect on climate is about the same, since the air and ocean exchange CO2 so freely: lowering carbon in the ocean would also draw down CO2 in the air.

Chemistry

A paper from the Naval Research Lab (Willauer et. al. 2010) outlines the process. Seawater is broken into hydrogen and oxygen through electrolysis; the oxygen is vented off and the hydrogen is retained. At the same time, CO2 is captured from a much larger volume of seawater. The CO2 is converted to carbon monoxide at first, then to hydrocarbons through the Fischer-Tropsch process. Chemically it looks like this:

34 H2O → 34 H2 + 17 O2 (Electrolysis)

11 CO2 + 11 H2 → 11 CO + 11 H2O (Reverse water gas shift)

11 CO + 23 H2 → C11H24 + 11 H2O (Fischer-Tropsch)

Combined, the process sums to:

11 CO2 + 12 H2O → C11H24 + 17 O2

That C11H24 you get at the end is the jet fuel.

Extracting CO2 from seawater turns out to be surprisingly easy, using a new method called bipolar membrane electrodialysis. Eisman et. al. (2012) have described BPMED and shown it can be done efficiently and fairly cheaply.

Cost

The Navy is interested in manufacturing jet fuel at remote locations, either remote islands or at sea. Electricity (mostly for the electrolysis step) is the main energy input and therefore the key cost driver. The NRL report envisions two types of electricity production to drive this process. For remote islands, they are looking at OTEC (Ocean-Thermal Electric Conversion), which generates power from the difference in temperature between the surface of the sea and the depths. For at-sea synfuel manufacturing, they are looking at existing Navy nuclear power plants, such as those currently found on submarines and aircraft carriers.

OTEC is not a mature technology, as there are no existing powerplants of this type anywhere in the world. Accordingly cost estimates for OTEC vary widely, and Willauer uses estimates ranging from $900 million to $1.5 billion for a 200 MW OTEC plant. Under these scenarios, the final cost of jet fuel would range from $5.78 to $8.70 per gallon, according to Willauer.

Although these costs are higher than current jet fuel prices, Willauer points out that generating fuel on site eliminates all transportation and storage costs for the fuel, which are considerable; therefore, even at these prices, on-site manufacturing of jet fuel might be cost-effective. Further, the cost of jet fuel has risen about fivefold since the turn of the century, and if those increases were to continue, synthetic jetfuel could quickly become the cheaper option.

For at-sea applications, Willauer assumes current Navy nuclear power plant capital costs of $1200/kW (which would be $240 million for a 200 MW reactor) in a ship costing $650 million. Under that scenario, fuel cost would be $5.74 per gallon, according to Willauer.

But Morgan points out that by beaching the reactor, that $650 million for the ship could be saved. Zeroing out the cost of the ship would result in synthetic jet fuel from seawater costing $3.00 per gallon, according to Morgan's spreadsheet. (Note that Morgan is a bit more conservative about process energy usage than Willauer, so the total fuel output from the 200 MWe input is different in the spreadsheet than in Willauer's paper.) That's about what jet fuel from fossil has cost on the open market for the past 2 years.

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Comment Preferences

  •  This sounds promising! (5+ / 0-)

    The Department of Defense has been testing a lot of alternative fuels under its current commander-in-chief. The Navy's is called the “Green Ship” initiative. The Army's is "Net Zero", for energy, water and waste. The Air Force aims to get half of its domestic jet fuel from alternative energies by 2016.

    Cheers to Dr. Morgan and to you for taking the time to write this interesting and hopeful diary!

    PS

    Could we get some of that electricity from concentrated solar so there's no risk of nuclear pollution? Please?

    "Let each unique song be sung and the spell of differentiation be broken" - Winter Rabbit

    by cotterperson on Fri Jan 18, 2013 at 04:13:39 PM PST

  •  Maybe (5+ / 0-)
    OTEC is not a mature technology, as there are no existing powerplants of this type anywhere in the world. Accordingly cost estimates for OTEC vary widely, and Willauer uses estimates ranging from $900 million to $1.5 billion for a 200 MW OTEC plant.

    we could divert the subsidies we give big oil to build some of these plants.....

    BTW, here's an interesting site that says taxpayers subsidize big oil as much as 52 billion a year. I never thought about how much we spend just to protect their tankers in the Persian Gulf....

    http://priceofoil.org/...

    "If fighting for a more equal and equitable distribution of the wealth of this country is socialistic, I stand guilty of being a socialist." Walter Reuther

    by fugwb on Fri Jan 18, 2013 at 04:32:03 PM PST

  •  Not clear why this is true (2+ / 0-)
    Recommended by:
    walkshills, Lujane
    it's easier (and cheaper) to remove carbon from the ocean than from the air,
    PV=kT.
    It should be quite possible to separate liquid CO2 from the air just by cooling it to the right temperature.  And doing that is a simple mechanical process.  Compress it, cool it, expand it again.  T will vary in an easily controllable manner, and you can set it for maximum liquid CO2.

    Hydrogen electrolysis is very energy intensive.  You're actually breaking bonds there.

    -7.75 -4.67

    "Freedom's just another word for nothing left to lose."

    There are no Christians in foxholes.

    by Odysseus on Fri Jan 18, 2013 at 05:02:31 PM PST

    •  You're confusing two different processes (5+ / 0-)

      Hydrogen electrolysis is required to get hydrogen, regardless of the method used to get carbon.

      Cooling air to get CO2 is certainly possible, but at just 390 ppmv, you need a LOT of air to get a tiny amount of CO2. The biploar membrane method runs electric current through acidified seawater, and CO2 bubbles up on its own. No cooling required.

      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 06:07:41 PM PST

      [ Parent ]

  •  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 ]

  •  No ones heard of? (2+ / 0-)
    Recommended by:
    FarWestGirl, Lujane

    Just what were the Germans doing in WW2?

    What got a patent in 1914?

    http://en.wikipedia.org/...

    Using hydrogen and carbon to make liquid fuels is old news. And God Damned if we need to stop using liquid fuels.

    FDR 9-23-33, "If we cannot do this one way, we will do it another way. But do it we will.

    by Roger Fox on Fri Jan 18, 2013 at 07:04:59 PM PST

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