Original URL: http://www.theregister.co.uk/2009/08/20/seawater_synthifuel_foolishness/

US Navy aims to make jetfuel from seawater uranium

Vampire-lust tales will rot your brain

By Lewis Page

Posted in Science, 20th August 2009 15:49 GMT

Analysis Coverage of recent US Navy research into producing jet fuel from CO2 and hydrogen has been widely reported under headlines such as "making jet fuel from seawater". The coverage illustrates not only declining modern understanding of science and technology, but also the sad eclipse of proper science fiction by vampire-lust fantasies.

The stories arise from a paper presented at the weekend by Robert Dorner and colleagues at the Naval Research Laboratory. According to the Navy boffins:

The impact CO2 is having on the environment has been thoroughly documented over the last years. Many different technologies have been proposed to reduce its impact on global warming such as geological sequestration. However, an interesting and attractive alternative would be the recycling of the gas into energy-rich molecules.

Dorner and Co have been working on mixing CO2 and hydrogen to produce light hydrocarbons which could then be processed into jet fuel. As jet fuel is rich in energy, doing this uses a lot of energy - and even then, a lot of the CO2 and hydrogen actually turns to methane. Methane can actually be a useful fuel, but not as useful as jetfuel - and as a waste product it's far more damaging to the environment than carbon dioxide, being a hugely more powerful greenhouse gas.

But Dorner and his colleagues have managed to get the amount of methane produced down to 30 per cent or so, using special catalysts. The "sea water" bit comes from the fact that Dorner has also noted that there's a fair bit of CO2 in sea water, plus hydrogen too if you have even more energy to crack water molecules apart.

If you were interested in being green, and had a whole load of energy which you considered green and wanted to make liquid fuel with, you probably wouldn't bother harvesting your CO2 from the sea - you'd get it from coal power stations or other hydrocarbon-burning powerplant exhausts. Such ideas are already commonly touted among researchers.

Enormous amounts of cheap carbon-free power aren't normally to be had, however, which is why such ideas remain mainly notional.

They aren't quite as notional for the US Navy, however. That's because US Navy aircraft carriers have powerful nuclear reactors aboard, potentially able to supply large amounts of energy if the ship wasn't going at full speed and launching planes (the reactors power the catapults as well as the ship's props).

As a result the primary limiting factor on how long a US carrier can keep flying its planes is actually the amount of jet fuel it can carry. The reactor's uranium lasts for years.

Thus it would actually be useful if you could build a plant on a carrier which could scoop CO2 out of the water, crack hydrogen from it too, and combine these to top off the ship's jet-fuel tanks. The carrier would be able to keep dominating airspace without needing to break off and replenish its supplies so often.

That's how Dorner may have presented the ideas to his bosses at the navy lab, perhaps. But when speaking to people concerned primarily about the environment, it's generally seen as silly to start mentioning nuclear power.

But there aren't really any other options for processes like this. Making synthetic liquid hydrocarbon fuels always consumes a lot more energy than you could get by burning the fuel, so it's mostly witless to make them using fossil power. (The US military is interested in making jet fuel using coal, but this is merely because America has a lot of coal mines and potentially not enough oil wells. The Germans who developed such processes originally did so for similar reasons.)

People would have known all this in the old days, because they read proper science fiction

In theory one might make synthi-fuel using renewable power, but that's not really on. Most analysis suggests that even the most extreme renewables plans would struggle to deliver as much energy as civilisation uses now. If the energy requirements of the transport sector increased by many times over - as it would if future transport ran on synthi-fuels made with CO2 - there'd be no hope of success at all.

A renewables-powered future might be possible, but it wouldn't have hydrocarbon synthifuel in it. Synthetic energy-rich fuel only makes any sense in a society which is largely nuclear powered, by fission or fusion.

It makes quite a lot of sense then, however: conceivably more sense than using hydrogen, the other widely-touted energy storage method in that scenario. Sure, hydrogen takes less energy to make, but it's much harder to handle and store with any safety - and its low density makes it difficult to use in many applications like aircraft. Hydrogen-fuelled planes would be mostly fuel tanks. Even hydrogen cars normally need to burn the stuff in fuel cells rather than combustion engines to get useful performance.

People in the old days knew all this. H Beam Piper - a man with high-school education who'd have been just as happy writing detective stories for better money - assumed in his sci-fi tales that the spacegoing Earthmen of the future would make "thermoconcentrate" (eg, "energy-rich" as Dorner puts it) synthi-fuels for use in vehicles not big enough to have onboard nuclear power, as other planets probably couldn't be relied upon to have handy underground reservoirs full of almost ready-made jet juice.

Sci-fi fans used to read writers like Piper: now they mainly read about vampire lust, seemingly.

And nowadays - I'm suggesting these things are linked - when a potential step forward in synthetic fuels is announced, it gets reported under the headline "jet fuel from water". When what you're actually talking about - in practical terms - is making jet fuel using uranium. ®