KitemanSA wrote:Joseph Chikva wrote:KitemanSA wrote: So you are telling me you know the reaction NH3 + NOx = N2 + H20 is endothermic?
I know that it does not matter is that reaction exo or end if you execute that reaction in exhaust system. Because even that will be exo, that from exhaust pipe will not make more work, but simply will heat up an environment.
Well DUHH!!!
Reading through this thread I noticed this argument went on (and on) for several pages and never got answered.
NH3 + NO = N2 + H20
Balance it
4NH3 + 6NO = 5N2 + 6H2O
Enthalpy of Formation for each from
http://en.wikipedia.org/wiki/List_of_st ... _formation
N2 = 0
NH3 = -27
NO - 80 (Highest of the common oxides i.e. most likely to be endothermic)
H2O = -237
Total of the reactants
-27 * 4 + 80 * 6 = 384
Total of the products
0*5 + -237 *6 = -1422
This reaction is exothermic.
On the issue of size of hydrogen production equipment, I can only offer the observation that a home electrolysis set up is small and rather high rate. Assuming constant current and that we care only about the amount of hydrogen, the weight in ,moles of hydrogen would be equal to the current times the time divided by Faraday's Constant i.e. A*T/(96,485) That's 96 thousand. To produce 1 mole per hour, you'd need 96,485/3600 or approximately 27 amps continuously for one hour. Assuming 110 volts, that's a bit less than 3kw to produce 1 mole of hydrogen.
1 mole of hydrogen weighs about 1kg. In producing it you will produce 1/2 mole of oxygen. The input is 1 mole of water, roughly 9 kg. Water has a volume of about 1 liter per kg (Salt water is a bit more) so let's assume a volume of at least 20 times that so that we don't have to deal with our electrolyte falling out of solution due to volume changes. A single 0.15 inch wire is capable of carrying that current and the whole apparatus will fit in a single cubic meter, exclusive of whatever you use to compress and refrigerate the hydrogen. If you're using the Haber-Bosch process you don't need to cool the hydrogen.
http://www.usni.org/magazines/proceedin ... ndence-oil
This article gives the Navy's oil usage at 33 thousand gallons every ten minutes. That's 198 thousand gallons per hour
This
http://www.energybulletin.net/stories/2 ... nd-figures
says that 75% of the Navy's fuel is used for vehicles. Let's replace that number with ammonia. Ammonia has roughly 1/3 the energy density of diesel and there are about 3.8 liters in a gallon.
Putting all of that together suggests we need to produce 1.7 million liters of ammonia per hour to run the entire Navy. Liquid ammonia weighs about 0.68 kg per liter. One mole of ammonia weighs 17 kg. We need roughly 68 thousand moles of ammonia per hour.
To produce one mole of ammonia takes one mole of N2 and 3 moles of H2 so we need 204 thousand moles of hydrogen per hour. Let's make the assumptions that all of the fuel we are replacing is used by ships or ship based aircraft and that all six fleets use an equal amount of fuel. So we need 34,000 cubic meters of hydrogen production per fleet.
Assuming that 1/8 of the ship's overall volume can be devoted to hydrogen production, that would be around 18,750 cubic meters per ship. So two ships per fleet.
Issues
If I didn't source it, it's probably inaccurate. At least a bit.
Ships volume was calculated from wiki, using waterline dimensions and I didn't attempt to calculate how much of that is superstructure. These ships have more than 1/8 of their volume available for mission, don't they?
Capturing nitrogen from the atmosphere should be compact but you'll need to remove the water vapor (probably) and oxygen. Removing oxygen is easy but what do you burn? You don't want to have to cool that volume of air (1.9 million liters) to a temperature where nitrogen is liquid just to heat it back up again. It's too much to burn. Zeolite, SPA are possible. This
http://humanresearchroadmap.nasa.gov/tasks/?i=801
suggests that a machine producing 4 liters of oxygen would weigh about 8 pounds and consume 106 watts of power. That means it also produces 15 liters of nitrogen per minute. for 1.9 million liters per hour we'd need 36 (
No, 2112) of them, consuming about 4 (
No, 232) kw and weighing less than 400 pounds (
No, less than 17,000 pounds) . That's not what I was expecting.
Edit: Originally, I used a rate of 15 liters per second, not minute. Sorry.
Aircraft range would be a problem. Like 1/3 of current. Needs work.
Storage!!!! Where/how? Replacing diesel with ammonia would be very expensive, I think. Isn't ammonia corrosive to rubber?
Probably other stuff I didn't think of.
Apologies for any errors. Does this sound reasonable?
