Airship Hydrogen resupply

[Alex K]

So, in my just-for-fun hard steampunk novel, an Airship gets stranded far from civilization because they have a Helium or Hydrogen leak. They want to replace the lost buoyant gas by newly made Hydrogen, and I was wondering whether that's feasible. So I'll take all of you brave folks through the numbers.

My template for the airship is the LZ104 "Afrika-Schiff", because it isn't too big, yet has a sufficient range for the story and with 50 tons a lot of payload capability to carry all kinds of nonsense relevant for the story.



It has 70 000 m^3 of Hydrogen. I assume that 10% of that are lost in an accident, so 7000 m^3, which is still a lot. The LZ104 would carry 1622 tons of fuel on its mission and was equipped with 5 motors with a whopping 240 horsepower each, corresponding to 180 kilowatts.

Now, my question was, assuming that the crew runs 1 ton of the fuel through one of the motors to generate electricity, how much energy would that be? Assuming perfect efficiency, a ton of petroleum gives you 4100 kWh. A 240 horsepower motor needs to run roughly 24 hours to do convert this amount of oil into energy, so that's realistic.

The question is now, how much Hydrogen do you get from those 4100 kWh of energy? Now, I assume that the crew finds some sort of alcaline material like KOH to pour into the water to do efficient electrolysis, splitting the water into O2 and H2. It turns out that under ideal conditions, one can generate 12 m^3 of H2 from one 1kW. That's good news, because the 4100 kWh would then be enough to make 50000 m^3, i.e. to refill almost the entire airship. This means that if we assume an overall efficiency of like 14% of the overall process of running the motor, making electricity and doing the electrolysis, the ton of oil is enough to replenish the missing 7000 m^3 of Hydrogen. That's not too far off the mark to make it realistic.

[Alex K]

p.s. if they lose a ton of fuel the need 1000 m^3 less buoyant volume, too...

[Jackalope]

Assuming perfect efficiency

[Thumpalumpacus]

Can I be the captain? I'll make you my First Officer.

[Minimalist]

Why not just feed the crew beans and have them fart into the gas bag?

[Thumpalumpacus]

That's methane, Min.

Christ, you're getting old.

[Minimalist]

According to this, it ought to work.

https://answers.yahoo.com/question/index...6041410506

If GAS Is Lighter Than AIR, Then Do We GAIN WEIGHT When We FART?

[Gawdzilla Sama]

So, in my just-for-fun hard steampunk novel, an Airship gets stranded far from civilization because they have a Helium or Hydrogen leak. They want to replace the lost buoyant gas by newly made Hydrogen, and I was wondering whether that's feasible. So I'll take all of you brave folks through the numbers.

My template for the airship is the LZ104 "Afrika-Schiff", because it isn't too big, yet has a sufficient range for the story and with 50 tons a lot of payload capability to carry all kinds of nonsense relevant for the story.



It has 70 000 m^3 of Hydrogen. I assume that 10% of that are lost in an accident, so 7000 m^3, which is still a lot. The LZ104 would carry 16 tons of fuel on its mission  and was equipped with 5 motors with a whopping 240 horsepower each, corresponding to 180 kilowatts.

Now, my question was, assuming that the crew runs 1 ton of the fuel through one of the motors to generate electricity, how much energy would that be? Assuming perfect efficiency, a ton of petroleum gives you 4100 kWh. A 240 horsepower motor needs to run roughly 24 hours to do convert this amount of oil into energy, so that's realistic.

The question is now, how much Hydrogen do you get from those 4100 kWh of energy? Now, I assume that the crew finds some sort of alcaline material like KOH to pour into the water to do efficient electrolysis, splitting the water into O2  and H2. It turns out that under ideal conditions, one can generate 12 m^3 of H2 from one 1kW. That's good news, because the 4100 kWh would then be enough to make 50000 m^3, i.e. to refill almost the entire airship. This means that if we assume an overall efficiency of like 14% of the overall process of running the motor, making electricity and doing the electrolysis, the ton of oil is enough to replenish the missing 7000 m^3 of Hydrogen. That's not too far off the mark to make it realistic.

If these maniacs can't help you try over at the Physics Forum. https://www.physicsforums.com/forums

I know I can't help, I'm mathgnostic.

[Gemini]

No obvious problems for a layperson with limited access to information relevant to the scene, if that helps. I have no idea where you would get exact specs on the petroluem-to-electrical-energy-efficiency of a Mayback HSLu engine, but I can't imagine that it would be lower than the value you used in your calculations.

Cool idea for a scene, btw.

[JuliaL]

Where did you find the 12m3/kWH number for electrolysis?
Grabbed from Wikipedia:
"a 100%-efficient electrolyser would consume 39.4 kilowatt-hours per kilogram (142 MJ/kg) of hydrogen,"
https://en.wikipedia.org/wiki/Electrolysis_of_water
This is ~40kWH per 11 cubic meters at STP.
http://www.engineeringtoolbox.com/gas-de...d_158.html

Your 4100kWH would then yield 4100kWH/(40kWH/11m3)=~1200m3.
But your genset is (charitably) 20% efficient, so you are only going to get 240m3.
Sorry


I'll take a different tack.

7000m3 of h2 at STP is going to mass 630kg with a MW of ~2gm/mol this is ~310000mols


You can get H2 from reacting aluminum with water using NaOH.

The following are possible reactions of aluminum with water:
2Al + 6H2O = 2Al(OH)3+ 3H2
2Al + 4H2O = 2AlO(OH) + 3H2
2Al + 3H2O = Al2O3+ 3H2
The first reaction forms the aluminum hydroxide bayerite (Al(OH)3) and hydrogen, the second
reaction forms the aluminum hydroxide boehmite (AlO(OH)) and hydrogen, and the third
reaction forms aluminum oxide and hydrogen.All these reactions are thermodynamically favorable from room temperature past the melting point of aluminum (660oC). All are also highly exothermic.

https://www1.eere.energy.gov/hydrogenand...drogen.pdf

Assume you can come up with the tools & plumbing, the reactions complete & there are no losses.
You'll have to scavenge 310000*2/3 mols of aluminum from your zeppelin (a mass of 5600kg) and make lots of NaOH from wood ash you make burning the hardwood forest you conveniently landed in.

This way you can use the ICE fuel to motor home.
You might include a 'will it make it home' sub-plot out of the fact that the crew had to rip 5.6 metric tons of structure out of "Afrika-Schiff" to generate her lifting gas.
Sacrifice an engine?