Hydrogen vs Gasoline

[Xeriar]

Water vapour does have a small greenhouse effect, but considering how much there already is in the atmosphere and how much more efficient CO2 is as a greenhouse gas, I don't think that we'd have to worry on that score.

I thought a molecule of h20 holds 120 times the heat a molecule of CO2 does?

 

[shecky]

I used to do that hydrogen baloon explosion for my museum outreach program. It was impressive. It was more impressive if you added Oxygen (bad adding some of your breath) to the mixture in the baloon.

Yikes! That sounds kinda scary.

I always wondered if one could make one of those hydrogen balloons explode by rubbing if on one's hair, like kids do to generate static electricity.

 

[pgwenthold]

Interesting notes on hydrogen (and other) energy sources here. One aspect I rarely hear about is hydrogen embrittlement which would seem a serious problem in any containment system.



What conditions would one find hydrogen at a filling station? Gas? Liquid?

The only demonstration i ever saw was many years ago, when a hydrogen filled balloon was ignited from several feet away. The explosion was rather dramatic. I wonder how a comparable amount of gasoline (vapor, I figure) would perform?

Pure hydrogen burns fairly duddily, as does pure oxygen. Sure, they burn, but it is more or less a burn. Moreover, this is in the gaseous state, where combustion is most efficient. I wouldn't be excessively concerned with liquid hydrogen. Liquid oxygen is really dangerous, but that is because of its reactivity with organic materials.

A mixture of hydrogen and oxygen, however, is a different story. The concussion of the oxygen/hydrogen explosion will bring down ceiling tiles.

Fortunately, hydrogen will diffuse fairly quickly through the atmosphere, such that any leak will not lead to significant concentration.

Ultimately, I wouldn't think a tank of liquid H2 would be any more dangerous than gasoline.

 

[pgwenthold]

Water vapour does have a small greenhouse effect,

While your ultimate point was valid, I should note that this is far understating the case. Water vapor has a _huge_ greenhouse effect.

 

[DaveW]

Pure hydrogen burns fairly duddily, as does pure oxygen. Sure, they burn, but it is more or less a burn. Moreover, this is in the gaseous state, where combustion is most efficient. I wouldn't be excessively concerned with liquid hydrogen. Liquid oxygen is really dangerous, but that is because of its reactivity with organic materials.

[snip]

Ultimately, I wouldn't think a tank of liquid H2 would be any more dangerous than gasoline.

Except that to stay in the liquid form, both hydrogen and oxygen have to remain pressurized. If a leak occured, the leaking hydrogen would flash to gaseous form quickly. Also, a pressurized tank has more dangers inherently than a non-pressurized tank (lots of stored energy in the form of pressure!)

 

[Ladewig]

I'm not a scientist, so please forgive the question.

Aren't the fumes from gasoline more dangerous to people living next to filling stations more dangerous than the possibility of gasoline or hydrogen exploding in those conditions?

 

[anor277]

@dave,
While I agree that a pressurized cylinder has inherent dangers whatever the gas (gas cylinders are one of the most dangerousthings you can use in a lab for instance), O2 (and dihydrogen?) do not have to be pressurized (i.e. more than 1 atm) to remain a liquid, they just have to be cold.

 

[pgwenthold]

@dave,
While I agree that a pressurized cylinder has inherent dangers whatever the gas (gas cylinders are one of the most dangerousthings you can use in a lab for instance), O2 (and dihydrogen?) do not have to be pressurized (i.e. more than 1 atm) to remain a liquid, they just have to be cold.

It's a lot easier to keep the stuff at room temperature and high pressures than to maintain a temperature of 2 K at atmospheric pressue.

The work required to maintain a temperature cold enough to keep it condensed at atmospheric pressure would probably require more energy than what you get from the hydrogen in the end.

 

[DaveW]

@dave,
While I agree that a pressurized cylinder has inherent dangers whatever the gas (gas cylinders are one of the most dangerousthings you can use in a lab for instance), O2 (and dihydrogen?) do not have to be pressurized (i.e. more than 1 atm) to remain a liquid, they just have to be cold.

True, but you can alleviate the temperature requirement (which could be a large load) by opting for higher pressure instead. I'm not sure what temperature/pressure requirement the "hydrogen economy" is shooting for, though.

--edit: What pgwenthold said, while I was typing

 

[pgwenthold]

And to expound the point, it is a heck of a lot easier to prevent particle transfer (even for something like H2) than it is to prevent heat transfer, which is what you have to do to keep it cold. A vacuum thermos is only so good, especially at the kind of temperatures we are talking here.

In fact, things that need to be run at liquid helium temperatures (superconducting magnets, for example) have a liquid nitrogen jacket around the dewar to minimize the heat transfer. Since liquid H2 is basically the same as liquid helium, you would have to do the same thing. So you have a tank of liquid H2 surrounded by a dewar inside a dewar of LN2.

Now, LN2 has a decent advantage in that the heat capacity is much higher than that for the small stuff, so it can stick around but even in the best of circumstances you'd be refilling the liquid nitrogen every day. Even at a bulk price of $1 a gallon, you need so much that this would get very costly.

Pressurize it and make life easier.

 

[SGT]

I
Do the protestors have a legitimate fear or do are they just thinking hydrogen=Hindenberg=BAD?

...a NASA scientist at Cape Canaveral has found proof that neither the hydrogen in the hull nor a bomb was to blame, but the fabric of the Hindenburg's outer skin and a new protective coating. A single spark of static electricity was enough to make it burn like dry leaves. The "infallible" German engineers had designed a flying bomb just waiting to explode.

See the whole story at:
http://www.vidicom-tv.com/tohiburg.htm

 

[jj]

Liquid oxygen is really dangerous, but that is because of its reactivity with organic materials.

Henh, not just.

Back in the '70's, I think (it's been a while) in Youngstown, Ohio, a full semi-truck of LOX was t-boned by a train consisting of a diesel that had just fueled that was pulling tank cars, at least the first two of which were fuel of some sort.

I have no idea if there is anything on that accident on the net. I suppose I should look.

Nope. It was pre-internet. Great mess it was, too.