iain wrote:
Right, I'm writing up the nuclear fueller idea for the Navy.
I made my own estimate for C(NH2)4, and it's not encouraging. I observe that methylamine (H3C-NH2) is CH4 with a H replaced with a NH2. The heat of combustion, all products returned to 25 C, goes from 890.8 to 1085.6 kJ/mol, an increase of 194.8 kJ/mol.
Taking a wild leap, I note that if I do that substitution 3 more times, I get C(NH2)4, and 1670 kJ/mol.
But the basic problem is that nitrogen just sucks for power density compared to carbon. 194.8 kJ/mol added for an increase of 15 g/mol is about 13 MJ/kg. Compare the equivalent substitution of H for CH3: 669.9 kJ/mol added for an increase of 14 g/mol, or 47.8 kJ/kg.
The Navy burns quite a bit more JP-5 than fuel oil. The gain of not having a fuel logistics tail is probably worth cutting the energy density in the ship's fuel store by a factor of 2. But I doubt it's worth cutting the plane's energy density by 2.
So, the problem is getting carbon. Getting it from the atmosphere involves gigantic air handling equipment. If my fueller has 1 GW(e) of reactor onboard, and attempts to make 400 MW of fuel, and that fuel is something like 50 MJ/kgC, then it needs 8 kg/sec of carbon. 385 ppmV of CO2 in the atmosphere is 160 mg/m^3. So, if we can get 90% of that CO2, we'd need to process air at 55,000 m^3/sec. That's a terrible problem.
A Supply-class fast combat support ship is 230 meters long, 33 meters wide, and has a draft of 12 meters. Imagine a similarly-sized nuclear fueller with nearly the entire superstructure consisting of a forced-draft cooling tower. The tower has intakes on each side of the ship, 15 meters tall and 250 meters long. Air flows through this tower at 7.4 meters per second (16 miles per hour). All of this sits on top of a chemical factory and PWR reactor set and blasts through the water at practically any speed it wants, because preposterous amounts of electrical power are available for the screws.
It would be really great to find a different way to get carbon.
Tow a net to capture microscopic calcified marine life, sea weed and the like detritus … and floating garbage mostly plastic of which there are giga-tones floating in the upper layers of water.
Your ship floats in a garage pile of almost unlimited scope and dimensions. You might as well utilize it.
The drag performance of this catchment net could be optimized by integrating into a water jet propulsion system… think jet sky.
A sortie of such a ship will do wonders for the purity of the oceans.