Zero emission synfuel from seawater Feb 6, 2013 11:50:04 GMT 9.5
Post by engineerpoet on Feb 6, 2013 11:50:04 GMT 9.5
That assumes we have been trying to build one. The effort was dropped when ICBMs became accurate enough to be a survivable deterrent.
A B747 at cruise burns fuel at about 200 megawatts. At the 22 kW/l figures I'm seeing for MSR concepts, a 200 MW(t) reactor would not be all that large; 9 cubic meters at a density of 3 would only weigh 27 tons. The performance demands go down as the cruise speed is reduced and the wing aspect ratio increased.
The longest-lived unstable isotope of aluminum heavier than 27 is Al-28, half-life 2.2 minutes. Typical alloying elements, copper and magnesium, are similarly resistant to neutron activation. Pray tell, what's going to be so nasty about this thing? A ground tug with a shadow shield could move it to parking, and mobile shields around the airframe would allow service; in the fuselage, water tanks fore and aft of the reactor(s) could be filled to provide shielding for the rest of the interior when on the ground. The airframe would have hardpoints for support when it was loaded with shielding water.
(the ones trialed in the 60s would only possibly work if the entire thing was unshielded, which would rapidly make the entire airframe far too hot for aircrew to approach even when teh reactors were cold... which makes maintenance rather... interesting)
As long as these things didn't have to ditch (dual reactors and triply-redundant flight systems, maybe?) you could service them just about anywhere. Get a few islands and fly them in monthly for service and fuel changes.
if synthetic fuels are really as expensive as you claim they would be then it would be better just to do the crossing in a 40+ knot nuclear ocean liner.
I'd much rather go to Australia at 400 knots or even 300 knots than 40 knots. Halfway around the world at 300 knots is only 36 hours. You could beam power to an aircraft to get it to altitude if you didn't feel like burning fuel. Rendezvous with the nuclear towplane, catch the towrope using something like a probe-and-drogue system (with electric power supply to power aircraft systems), and you're good for transoceanic legs. Your fuel reserve needs only to get to the nearest emergency landing site with clear weather.
Additionally, SOECs don't have "huge capital costs"... since by the very nature of the high temperature process they don't require that many very expensive materials in the construction of the equipment.
It's not the fuel processing, it's the power to drive it and the reactors to generate it; a system sized to supply our current needs via synthetic fuel plants is going to consume more input power than our current grid. That needs a dedicated power supply (no off-peak rates here). That's the big problem with the Green Freedom idea.
There are substantial losses in conversion, roughly equal cost of CO2 capture to hydrogen generation, and so on. Then you have to carry a full load of fuel for takeoff, climb and the first half of the longest leg, with the associated induced drag and its cost in fuel. A reserve fuel supply for a towed aircraft launched on beamed power need be sufficient only for the second half, descent and landing. And, of course, if everything works right you don't need to burn it; you don't care very much what it costs because it's strictly for emergencies. The rest of your useful load is payload, not fuel.
It is really suprisingly cheap when you can run your equipment ~8-10hrs a day every day on electricity priced at ~1-2 US cents/kWh and stockpile the methanol/syngas for use during the peak periods.
I like the idea from a number of angles, I'm just not sure it makes economic sense when you can use a nuclear energy supply directly. If an SOFC/syngas system works as a battery, it would be a great thing.
Hmmm. There's an idea, make the SOFC bi-directional. You feed it CO2 and H2O to generate a regular surplus of syngas for high-value products, but its main use is as an electrical power buffer on a daily cycle. You size it for the worst-case day/night demand differential.
Converting nuclear power to (heavy, bulky!) chemical energy to be carried long distances loses many of the advantages of nuclear energy right there. Eliminate the middleman, if possible.