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Catalytic scrubber for H2 airships

safety boy rides again
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Hydrogen airships are better than airplanes in many ways: cleaner, quieter, more scenic and interesting, more resistant to volcanic ash, and arguably safer. Although airplanes crash and burn and kill everyone aboard on a regular basis, people are desensitized to it. Yet, even mention hydrogen airships and people freak out: ZOMG ZOMG we're all gonna die!

Anyway... on to the idea. The biggest safety issue with H2 airships is the mixing-in of oxygen with the lifting gas. Oxygen can get into the envelope through leaks or by osmosis, eventually reaching a mix ratio that is explosive. So, I propose that one safety feature of modern airships would be a pump or fan that continually circulates the lift gas through a catalytic converter, consuming whatever oxygen has found it's way into the mix. The catalyst would have temperature alarms to warn of excessive oxygen levels, and would be enclosed by spark arresters to avoid flashback.

afinehowdoyoudo, May 19 2010

helium shortage http://www.usatoday...-12-02-Helium_N.htm
[afinehowdoyoudo, May 19 2010]

Steam Balloon Steam_20balloon
Steam Surrounded by air (without hydrogen) [goldbb, May 25 2010]

[link]






       Yes, helium: a rare, expensive and non-renewable resource. A dead-end until fusion reactors become practical..
afinehowdoyoudo, May 19 2010
  

       Sure 21, just nip over to the Sun and grab a few megatons of helium for us. It s true, there is UP TO 7%, in certain deposits of natural gas, purified at substantial cost, and when it escapes, its gone.. unless you grab your skyhook and catch it.
afinehowdoyoudo, May 19 2010
  

       Is the mixing in of oxygen the biggest problem? The Hindenburg did not explode; it burned.   

       My personal problem with airships is the slowth.
bungston, May 19 2010
  

       Well, the Hindenberg burned mostly because of the skin being made of extremely flammable material. If that obvious failure mode is remedied, the next big risk to consider is the formation of an explosive mix inside the blimp. That would happen on long-shot odds due to leaks or malfunction, or more slowly and deterministically from diffusion (osmosis) through the skin. The consequences of an exploding hydrogen/oxygen mix are much more severe than of burning a bubble of pure hydrogen. Much much much   

       Being slow (the German zeppelins traveled at about 75 mph) could be seen as an advantage for low-altitude sightseeing travelers, or as part of the business model for cargo haulage, or as a trade-off for lower fuel consumption and environmental impact. I don't expect that airships would ever replace airplanes, but there is (should be) a place for them in the mix of transportation options. Hydrogen airships are good because the lift gas is the most sustainable choice, and could be part of a hydrogen fuel infrastructure. Wouldn't it be nice if? *shrugs resignedly*
afinehowdoyoudo, May 19 2010
  

       How stable is oxygen in a hydrogen environment? Or hydrogen in an oxygen environment? My understanding of the latter is that the H2 spontaneously oxidizes. I wonder if this would prevent O2 buildup?   

       One might facilitate this by having superheated coils hanging around in the hydrogen. This would be lighter than blowers and scrubbers. The red hot coil would catalyze the formation of H20 from any small amount of O2 in the vicinity. Plus if large enough the coil would cause the airship to glow awesomely at night.   

       Also, instead of a resigned shrug I suggest you bang your monitor with your shoe, typing H2! H2! with the other hand.
bungston, May 19 2010
  

       [afinehowdoyoudo], Mythbusters tested that one, and though they found that the skin of the Hindenburg did contribute to the rapid burning of the zeppelin, it was by no means "mostly" responsible.   

       Anyway, this idea is only any good assuming no breach of the hydrogen cells. If the hydrogen leaks into the outside atmosphere, no catalytic converter in the world will help you. It's a nice safety feature, but basically worthless in the event of a serious crash.   

       Along the lines of those defending the flammability of hydrogen, many people also forget that jet airplanes are full of jet fuel, which is also highly flammable. I too agree that the fear of hydrogen blimps and zeppelins is overblown, but this idea isn't a cure-all either.
5th Earth, May 23 2010
  

       // until fusion reactors become practical.. //   

       We have a brochure that may interest you ...   

       // just nip over to the Sun and grab a few megatons of helium for us //   

       We accept all major credit and charge cards. We can do it for you wholesale.   

       Oxygen in the lift gas isn't a great problem; and in WW1, the British thought that the Zeppelins pumped their oxygen-poor engine exhausts into the envelope to quench any risk of ignition due to tracer-type machine gun projectiles (this was later shown to be completely erroneous).   

       DELAG, the joint-stock transport company set up partly by Zeppelin, was extremely sucessful, carryig thousands of passengers without a single casualty.   

       Hydrogen-filled airships are safe and practical, barring sabotage or deliberate attack. It's the Hindenburg which has left an undeserved legacy of distrust in the technology.
8th of 7, May 23 2010
  

       Perhaps a layered balloon approach?   

       A hydrogen balloon, surrounded by a steam balloon, surrounded by a hot air balloon.
goldbb, May 23 2010
  

       A bromine balloon layer would help with leak detection.
bungston, May 24 2010
  

       Would that be because leaks in the bromine layer would happen long before the vehicle operator becomes lax in looking out for them?
goldbb, May 24 2010
  

       Well, *obviously* a bromine balloon layer would help with bromine leak detection.
It's damnably hard to detect bromine leaks if there isn't any bromine.
mouseposture, May 24 2010
  

       //Is the mixing in of oxygen the biggest problem?//   

       If oxygen is getting in, far more hydrogen is getting out, as the diffusion rate of hydrogen through most materials is an order or two greater than air. So this idea might work better for other gases, such as for methane in coal mines.
ldischler, May 25 2010
  

       The speed issue is the main problem with airships - not necessarily because of the leisure element (I'd love to see cruise-liners in an airship format for example) but due to prevailing weather conditions. If for example you want to travel East at a maximum ground-speed of 75mph, but the wind happens to be blowing west at 80mph (which, at altitude is not unlikely) it's just not commercially viable to have your timetables very literally at the mercy of the weather.   

       Solve the speed problem, and you'll usher in a new era of air-travel. I quite like the "tacking" approach used by ships sailing against the wind, translating that technique into an airship-viable model would be tricky though.
zen_tom, May 25 2010
  

       // translating that technique into an airship-viable model would be tricky though //   

       Actually, it would be impossible.   

       "Tacking" requires the interaction of the wind force on the sails with the opposing force applied by the hull of the ship/keelboard and the rudder.   

       The ship is "in" the water and the air simultaneously.   

       Land yachts are the same; they rely on friction between the wheels and the ground.   

       Any aircraft, decoupled from a solid surface, has no such fixed medium to exert force against; it has only the air it is in, and the power of its engines, if any. Gliders progress by gaining height using thermals, then trading that height for speed (= motion over ground).
8th of 7, May 25 2010
  

       //shortage is caused not by rarity of the gas, but by extraction plants not running at full capacity //   

       I think the point is that helium is expensive to distill, and will always be expensive to distill. That makes it relatively rare in pure form.   

       Further, I think you know this and that you are just being a rump scrumper for the hell of it.
nomocrow, May 25 2010
  

       Why a steam layer? If we want a light vapour, then lithium could be a winner. Much lighter than water vapour.
saedi, May 25 2010
  

       Or... Make the atmosphere heavier. Large amounts of SF6 would do the trick. Then we could use air that doesn't have SF6 in it to fill airships. Nothing would burn and they could life several times as much.   

       Replacing all the nitrogen in the atmosphere with a heavy gas like SF6 would give everyone super deep voices by lowering the speed of sound. It would bring musical instruments back into the hearing range of old people. While also making normal aero-lift more efficient.   

       Win, win, win..!
saedi, May 25 2010
  

       //Why a steam layer?//   

       Firstly, at any given temperature above 100C, steam is less dense than air, thus it provides better lift than hot air.   

       Secondly, while we can expect a hot air layer to contain a certain amount of oxygen, the steam would start out as liquid water, and thus not have any significant initial quantity of oxygen in it... any oxygen in the steam would have had to leak or diffuse inwards from the surrounding hot air.   

       Third, if the catalytic scrubber were placed within the steam layer, any resulting water would be exactly where we want it to be.   

       As ldischler said, hydrogen will diffuse outwards faster than other gasses will diffuse inwards; hydrogen getting into the air in the outer balloon is more of a concern than oxygen getting into the hydrogen envelope. Furthermore, according to Wikipedia, "Hydrogen gas forms explosive mixtures with air in the concentration range 4-74% (volume per cent of hydrogen in air)." Thus, it takes a lot of air (26%) sneaking in to form an explosive mix, compared to a little hydrogen (4%) sneaking out.   

       //lithium could be a winner//   

       Ignoring the cost, using lithium would create more hazards than it prevents... for example, someone might steal the balloon for making meth.
goldbb, May 25 2010
  

       //Tacking//   

       // translating that technique into an airship-viable model would be tricky though //   

       //Actually, it would be impossible. //   

       Impossible yes, but if the shape of the zepplin could morph so that one side flattened while the other side remained a half teardrop then a head wind could be used to controll drift to one side or the other by the camber creating lower air pressure on one side of the craft than the other no?
hmmm, suddenly dimpling one side would have the same effect without it having to morph.
  

       /suddenly dimpling one side would have the same effect without it having to morph/   

       cool idea
bungston, May 25 2010
  

       Hydrogen in air may ignite at 4%, but the flame speed is so slow that it cannot propagate downwards (the flame rises as it's warm). So when it hits the top of whatever it's in, it goes out. This stops being a problem at about 5.5%. Where if you're lucky, it doesn't go out. From there to about 6.5%, the flame moves slowly and does not get too hot. You can have a large plastic bag of it and light it and the bag does not burst. Above 6.5% it rapidly gets more violent. From 7.5% on, it shreds the bag or test chamber and makes customers jump and doors blow open.   

       Really don't like using hydrogen mixtures for fuel systems testing... DO-160F specifies these mixtures.   

       For interest, Hydrogen 6%, Oxygen 12%, Argon 82% mixes are usually used which is particularly fun when the Argon bottle runs out.   

       So, at low concentrations, the problem is variable. From a strange and gentle additional heat source to a bomb...
saedi, May 26 2010
  

       //you are just being a rump scrumper // [+]
coprocephalous, May 26 2010
  

       Why argon? Why not nitrogen? Nothing against argon, which has a sweet name. But I have to think it is spendy.
bungston, May 26 2010
  

       The reason lays in it's very low heat capacity. This makes it more sensitive for a less energetic reaction. However, it also lowers the breakdown voltage of the mixture, making sparking more likely. These positives really don't seem to out weigh the negatives in my book though.
saedi, May 27 2010
  

       really it's not that dangerous just to use hydrogen and modern measuring, containment and fire proofing practices.   

       For this idea you could also use a sacrificial electrode. Create an arc between a metal or substances that oxidizes rapidly in the presence of oxygen or nitrogen, but not in the presence of hydrogen.   

       We use sacrificial electrodes of chromium or titanium in inert atmosphere chambers for welding. If you strike an arc on titanium it will rapidly oxidize eating up the remaining moles worth of oxygen relatively easily. Thus getting you to the below 1PPM tolerances for some types of welding.
metarinka, May 28 2010
  

       /substances that oxidizes rapidly in the presence of oxygen or nitrogen, but not in the presence of hydrogen. /   

       Like hydrogen! Except for the nitrogen part.
bungston, May 28 2010
  

       /If you strike an arc on titanium it will rapidly oxidize eating up the remaining moles worth of oxygen relatively easily/   

       I like this, especially for eating up moles of oxygen inside a hydrogen balloon. I like it at some distance.
bungston, May 28 2010
  

       One of the first man-carrying balloons attempted to combine the advantages of hot-air and hydrogen balloons, by stacking one on top of the other. The hot-air balloon, with its burner, was underneath.   

       On its maiden flight, it exhibited a characteristic failure mode.   

       Now, for extra credit: why did it fail in this manner?
(The obvious answer is not the correct one.)
mouseposture, May 29 2010
  

       The hydrogen warmed up and escaped it's envelope. Hilarity ensued when it encountered the flame or a portion thereof from the hot-air part.
FlyingToaster, May 30 2010
  

       [FT], I said the obvious answer is not the correct one.
  

       There was a rope actuating the release valve, at the top, running to the crew compartment (i.e. basket) at the bottom. As the intrepid French aeronaut tugged, the rope rubbed against the silk balloon. Static electricity built up, and a spark ignited the hydrogen.
  

       If that seemed to you like the more obvious answer, then you have a *very* interesting mind.
mouseposture, May 30 2010
  

       That woulda been my next guess.   

       This idea is very similar to catalytic caps that they put on batteries to keep the H2 down.
FlyingToaster, May 30 2010
  
      
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