The US navy has been investigating the production of fuel from seawater using electricity from ship’s nuclear power systems for a number of years.  This process would allow aircraft carrier task forces to stay at sea longer without depending on vulnerable fuel tankers to keep the planes flying.  The navy has now announced that they have successfully used the fuel from their pilot plant to fly a plane with an internal combustion engine.  (Well, OK a model mustang.)

The process used involves electrolysis of sea water to produce CO2 and hydrogen followed by a catalytic reaction to produce hydrocarbons.   There is nothing radically new here.  Hydrogen has been produced commercially using electrolysis for a long time.  There are also well established commercially available processes for converting mixtures of hydrogen and nitrogen or hydrogen and CO2 into a range of useful chemicals and fuels.  My guess is that most of the effort taken by the US navy has been focused on developing a process that could fit into a small part of an aircraft carrier.

The potential of these types of development go well beyond the needs of the US navy.  Think about it: Unless there is an amazing breakthrough, renewable power plus batteries are not going to be able to deliver 100% renewable transport.  Renewable power + batteries is not going be suitable for long distant flights, travel in the Australian outback or long distance sea travel.  There is a need for energy intensive transportable fuels to cover these needs.

Bio-fuels are not the answer.  Diversion of land to the production of bio-fuels is already causing starvation of people in some countries as well as damage to the environment.  (Think jungle clearing for palm oil production.)  In addition, the production of bio-fuels is vulnerable to climate change and pests as well as posing potential problems if the organisms used escape into the wild.  What is needed are low impact renewable fuels produced by inorganic processes such as the US Navy process mentioned above.

The easiest low impact renewable fuel to produce is liquid ammonia.  It is easy to produce because all it needs is water, nitrogen from the air.  It may be practical to locate both power source and fuel production close to where it is needed thus doing away with the need to transport fossil fuel based fuels all the way from well to consumer.  Ammonia can be used as a transport fuel in internal combustion engines and gas turbines with only minor engine modifications. (It needs about 5% biodiesel in the mix for diesel engines.) Ammonia used as a fuel can be stored and handled in a similar way to LPG.  However, ammonia has lower energy densities compared with conventional fossil fuels. (43% by weight compared with Jet A fuel.)  This is a serious disadvantage if we are talking about air transport.

It is worth noting that most of the ammonia produced today is made from dirty hydrogen produced from natural gas.  The major use of ammonia is nitrogenous fertilizers.  Cleaning up the production of nitrogenous fertilizer and other nitrogenous compounds is a bonus that comes with replacing dirty hydrogen with renewable hydrogen.

In the short term cleaner hydrocarbons could be produced using waste CO2 from sources such as steel and cement production.  In the longer term the main source of CO2 would have to be the ocean.  Keep in mind that renewable hydrogen + CO2 can be used to clean up the petrochemical industry as well as transport fuel.


  1. Good to see you again, John D. I know the oceans are vast and deep but what are the chances of having a runaway demand for fuel based on seawater?

    Manned strike and interceptor aircraft are heading towards extinction – not just yet though – so the hydrocarbon fuel demands of missiles and unmanned aircraft are only a fraction of those of manned ones and, in some cases, they may not need hydrocarbon fuels at all.

    Also, aircraft carriers, as such, will have less and less strategic value in future – though I think there will always be a demand for capital ships, by nations that can afford them, as prestige and intimidation vessels. These are large multipurpose ships that are sometimes called “a portable war” – ships of this type will still need some of the traditional liquid hydrocarbon fuels for helicopters, armoured vehicles and the like.

  2. Graham: You are right about changing strategic needs. However, for a country that is trying to project naval influence well beyond its borders, nuclear powered ships have obvious advantages, including the possibility of being a floating fuel factory.

    this US navy link gives more details including

    The predicted cost of jet fuel using these technologies is in the range of $3-$6 per gallon, and with sufficient funding and partnerships, this approach could be commercially viable within the next seven to ten years. Pursuing remote land-based options would be the first step towards a future sea-based solution.

    The real purpose of this post was to talk about low impact renewable fuels. To my mind they have to be part of any credible plan for 100% renewable transport plan. Ditto any 100% renewable nitrogenous chemical and petrochemical plan.
    To my mind we might be better off if some of the effort going into bio-fuels was diverted to non bio-fuels produced from renewable electricity.

  3. Non-biofuels sounds good – so long as making them doesn’t stuff up the oceans or the atmosphere.

    Have just taken a look at the Solar impulse site – and thought about where that could lead. In terms of dominating the air: supersonic aircraft chewing up huge amounts of liquid hydrocarbons may not always be the best way of doing that. In terms of airborne scientific platforms, the next generation of Solar Impulse aircraft might be as close as we’ll ever get to a flying perpetual motion machine. Then there’s the possibility of hybrid solar powered dirigibles kept aloft by hydrogen,

    Gee, it’s all happening. What a great time to be alive. :-).

  4. Meant to post this a while ago, John, but misplaced the link:

    I can’t say it looks all that feasible 😉 As I’m reading it, to produce enough fuel for a single F22 would require processing something like 250,000 m³ of seawater.

    The ammonia stuff is interesting. I like the idea of farmers being able to produce their own fertiliser from their wind turbine…

    But as far as ammonia as a transport fuel goes, all I can think is ACID RAIN!!

    Not sure how the public would warm to that.

  5. Interesting link Nick. $US6/gallon is roughly $aus/litre of $1.50. It is also worth noting that the calculation puts a price on power that doesn’t reflect the negligible cost of producing power from an existing nuclear power plant (Or surplus renewable power.)

  6. Nick: Burning ammonia will produce nitrogen oxides but i couldn’t easily find any details. I seem to recall that the catalytic converter in car exhausts broke down the nitrogen oxides to reduce LA smog so they may be able to deal with ammonia as a fuel
    In terms of 250,000m3 sounding a lot it would not seem much in terms of industrial pumping. I would imagine that the electrolytic cells that the salt water has to flow through would be low down in the air craft carrier. The high volume is all about producing the CO2 required to produce jet fuel.
    Ammonia production would need a fraction of this because only 1.35 kg of water will produce all the hydrogen needed to make one kg of ammonia.
    Looking at the quoted cost the increase cost per litre could be offset by better fuel efficiency.

  7. Nick: If you take a typical car that travels less than 20,000 km per year and assume the 5 litres per 100 km that many cars run at a one dollar per litre price increase costs $1000/yr ($19/week) – Hardly a show stopper if we are determined to do something about emissions and hunger.

  8. In terms of 250,000m3 sounding a lot it would not seem much in terms of industrial pumping. I would imagine that the electrolytic cells that the salt water has to flow through would be low down in the air craft carrier. The high volume is all about producing the CO2 required to produce jet fuel.

    John, the issue isn’t the pumping of 250,000 m³ of seawater per day. It’s the processing of 250,000 m³ of seawater per day.

    Hadera desal plant in Israel is one of the largest in the world:

    It can process 525,000 m³ of seawater per day. It also has a footprint of 1000m x 150m, which is at least 3 times larger than the largest supercarriers…

    But – synthesising jetfuel from seawater is far more complicated than desalination…

    Not surprising, since it hasn’t been achieved yet at any scale larger than 3 or 4 millilitres of ‘theoretical fuel’ produced per hour. Theoretical, because that hour is only the time it takes to extract the CO₂ and H₂, not the additional time it takes to actually produce jetfuel from them.


    Note that the process requires 1/5th as much seawater again per day just to supply the electrolytes…

    So scale up to 10 fighter planes instead of 1, and you’d need a desalination plant the size and scale of Hadera to produce potable quality water *just to supply the electrolytes*.

    Can you see why this makes no sense?

    Scale up to the 70-100 planes you’d find on a nuclear-powered supercarrier, and you’d need 7-10 desalination plants the size and scale of Hadera *just to supply the electrolytes*.

    Those costs were definitely not included in the feasibility study I linked to earlier.

    And, remember, that’s quite aside from the 25,000,000,000 litres of seawater you’d need to pump in and out per day to extract enough CO2 to fuel 70-100 planes.


    Three-way catalytic converters (TWC) have the additional advantage of controlling the emission of nitrogen oxides (NOx), in particular nitrous oxide, a greenhouse gas over three hundred times more potent than carbon dioxide,[15] a precursor to acid rain and currently the most ozone-depleting substance.[16] Technological improvements including three-way catalytic converters have led to motor vehicle nitrous oxide emissions in the US falling to 8.2% of anthropogenic nitrous oxide emissions in 2008, from a high of 17.77% in 1998.

    I assume the reduction in NOx could potentially be improved a lot if you weren’t having to worry about dealing with carbon monoxide as well. You’d have to hope so, because ammonia-fueled transport would increase NOx emissions one-hundred-fold!

  10. Nick: I cant see the size of a desalination plant having any relationship at all to the size of a jet fuel plant.
    I would also assume that the US navy cost study is not absurd. It should be relatively easy to to scale up the electrolysis part and the post electrolysis part is well established commercial practice.
    Unfortunately I have no feel for the size etc, of these plants and how well they would fit into an aircraft carrier.
    I would assume that the aircraft carrier would carry large reserves of jet fuel. This means that the plant would be far smaller than what would be required when the air craft carrier was fighting a pitched battle.

  11. “Nick: I cant see the size of a desalination plant having any relationship at all to the size of a jet fuel plant.”

    John, sorry if I wasn’t clear.

    1) A jetfuel plant such as the navy is researching requires a huge volume of *clean* water to supply the anolytes and catholytes with.

    2) The only way to remotely source a huge volume of clean water on an aircraft carrier is also from seawater.

    3) Hence, the researchers’ model jetfuel plant necessarily contains a desalination stage (see Figures 3 and 5 in the report linked to above. Note that it’s by far the largest physical component on the skid)

    4) Scale that desalination stage up to the amount of fuel required for just 10 fighter planes, and you quickly exceed the size and scale of the largest desalination plants in the world.

  12. I will need to read the fine print but I would have thought that there is no need for desalination of the sea water. There may be a need to to clean the water to remove mud and other gunk as well as killing organisms that would grow in pipes etc..
    The flow diagram suggests that hydrogen and CO2 production would be separate.

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