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  #1  
Old 09-30-2002, 03:49 PM
LilShieste LilShieste is offline
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Hydrogen fuel-cell vehicles

I just finished reading an article in the latest Scientific American about how hydrogen fuel-cell cars will be the next best thing since petroleum internal combustion engines.

My question is this: Isn't Hydrogen an extremely reactive element? (I mean, in the Periodic Table it's on the opposite end from the Noble Gases, so...) Am I just missing something about how we can store Hydrogen safely? Or did SA just not feel like addressing that particular issue?

Note: I feel my question here belongs in GQ, but I could easily see this making it's way into an IMHO thread or something.

LilShieste
  #2  
Old 09-30-2002, 03:57 PM
AndrewL AndrewL is offline
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Hydrogen will burn in the prescence of oxygen, but needs an ignition source - it won't burn spontaneously on its own. Hydrogen won't normally react with the walls of the tank or any other part of the fuel cell system. It takes the prescence of the platinum catalysts in the fuel cell to make it react at room temperature with anything normally present in the car.. It's really not any more dangerous than gasoline to store.
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Old 09-30-2002, 04:11 PM
Hail Ants Hail Ants is offline
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Another thing that makes it a little more dangerous in terms of using it in cars is that, unlike gasoline, hydrogen has to be stored in high pressure gas bottles (like scuba tanks). In a way though, this makes it safer because these high pressure tanks are a lot stronger than regular automobile gasoline tanks.
  #4  
Old 09-30-2002, 04:20 PM
Padeye Padeye is offline
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Try to keep things in perspective. Gasoline is far more dangerous than many alternative fuels but we're used to it and don't give it a second thought. Break open a gasoline tank and you have a flammable fuel that stick to everything... like people. A flammable gas burns but quickly dissipates. Also don't use the Hindenberg as an example of how hydrogen burns. All the visible flame was from the dope covered fabric covering the ship.

Lots of big problems to overcome with hydrogen as a energy carrier but safety is as much public relations as technical.
  #5  
Old 09-30-2002, 04:23 PM
Colophon Colophon is offline
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In a previous incarnation, about two years ago, I wrote an article on fuel-cell vehicles - it's available online <url=http://www.chemsoc.org/chembytes/ezine/2000/kingston_jun00.htm>here</url>. (Dang, there goes my anonymity )

I touched on the storage problem in the box towards the end. There are ways to adsorb hydrogen onto metal alloys or carbon nanotubes, which is safer than carrying liquid H2 around and also avoids the need for refrigeration and/or insulation.
  #6  
Old 09-30-2002, 04:43 PM
Colophon Colophon is offline
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Doh - didn't catch it in time. Fixed link here.
  #7  
Old 09-30-2002, 05:36 PM
rowrrbazzle rowrrbazzle is offline
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I know that hydrogen isn't reactive, unlike lithium or fluorine. My question is: Why? You could consider that it needs another electron to complete a shell, like fluorine. Or you could regard it as "wanting to" donate that electron, like lithium. I think this is really what the OP was getting at, and I'd welcome any insight. Completely ignorant speculation: do those two tendencies cancel out somehow?

I also know hydrogen usually exists as a molecule, H2. Lithium and fluorine don't, AFAIK. Is this why hydrogen is not as reactive as lithium and fluorine? Is monatomic hydrogen extremely reactive (I would guess yes).
  #8  
Old 09-30-2002, 08:14 PM
Sam Stone Sam Stone is offline
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If you think that hydrogen is safer than gasoline, ask yourself this: Would you like to be in an underground parking garage with a car that has a leaky hydrogen tank?

Also, doesn't hydrogen heat up when it is released? I seem to recall that a jet of hydrogen leaking from a tank will spontaneously heat up to the point where it can even ignite itself. But maybe I'm wrong about that.

Then there's the pressure vessel itself. I don't want to be in a car with a 3000psi hydrogen tank. I've seen what happens when SCUBA tanks rupture, and that's carrying a lousy 72 cu ft. of gas.

Hydrogen has a much lower power density than gasoline, which means you have to carry a lot more of it by weight to have the same range. A 20 gallon gas tank weighs about 130 lbs or so, if memory serves. How big a tank do you need to have, under what kind of pressure, to get the same amount of hydrogen into it?

Then there' the question of where the energy comes from. A lot of people who think hydrogen power is a solution to *energy needs doesn't understand that we can't mine for hydrogen - we have to create it. And creating hydrogen takes energy - more energy than you get back out. So hydrogen should be thought of more as an energy storage technology - not an energy source.

A Canadian engineering company has estimated that it would take 174 CANDU nuclear power plants to generate enough electricity. Until you can get the environmental lobby to agree to build 174 nuclear plants, or an equivalent number of coal or natural gas generators, you can't generate the hydrogen in the first place.

Another point is that we still need to refine crude oil to get other byproducts we need. Right now, the price of plastics, kerosene (Jet fuel), and other petroleum byproducts are artificially low because the demand for gasoline outstrips the demand for these byproducts. If you get rid of gasoline use, the price of other petroleum products will rise.

So what's the primary benefit of hydrogen? Lack of pollution. The power can be generated far away from population centers, and then consumed in a 'clean' way. In the meantime, the power generation can be nuclear with no emissions, or even if it's coal or natural gas it can be produced cleaner than in cars, because a big power plant can put heavy, complex scrubbers in place that are impractical for a car.

The problem with that, however, is that it's a solution for a problem that is fading away rapidly. Modern cars have very low emissions. Some of the newest gasoline powered cars actually qualify as zero-emission vehicles because they are so clean. So clean, in fact, that some of them emit cleaner gases at the tailpipe than they suck in through the intake.

I think the future for cars is hybrid gas/electric, with the duty cycle of the gasoline engine gradually getting smaller as electric motors and battery technology improve. There's a place for hydrogen fuel cells as well, but I'm not sure it'll be in cars.
  #9  
Old 09-30-2002, 08:16 PM
Sam Stone Sam Stone is offline
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I should clarify - The Canadian company estimated 174 CANDU reactors to create enough energy to produce enough hydrogen to replace gasoline usage in vehicles in the USA.
  #10  
Old 09-30-2002, 09:32 PM
scr4 scr4 is offline
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Quote:
Originally posted by Sam Stone
Would you like to be in an underground parking garage with a car that has a leaky hydrogen tank?
How is it worse than a leaky gasoline tank?

Quote:
Also, doesn't hydrogen heat up when it is released?
No, gas cools when it expands. Canned air feels cool, doesn't it?

Quote:
Modern cars have very low emissions. Some of the newest gasoline powered cars actually qualify as zero-emission vehicles
You can never eliminate CO2 emissions if you stick with gasoline.

I'm not convinced those 174 reactors will be a problem. I'm sure the American public will go for it if the price of oil climbs high enough. Admittedly that's a big "if".
  #11  
Old 09-30-2002, 11:41 PM
Sam Stone Sam Stone is offline
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Hydrogen is an explosive gas. Gasoline mostly stays liquid. Big difference.

As for hydrogen heating when it is expanded, this is what I was thinking of:

Quote:
The gas may be either heated or cooled by the expansion, depending upon the initial temperature and the particular gas. For most gases at room temperature, expansion results in cooling, as anyone who has used an aerosol can or operated a carbon dioxide fire extinguisher has experienced. Compressed air initially at 273 K, for example, will drop about 1/4 K for each atmosphere drop in pressure, while carbon dioxide will drop 11/2 K for each atmosphere drop in pressure. The temperature below which an expansion produces cooling is called the inversion temperature; it is high for most gases, but for hydrogen, it is about 193 K. Hydrogen, therefore, must be cooled below this temperature before it is expanded.
Cite: http://www.hq.nasa.gov/office/pao/Hi...404/app-a1.htm

The 174 CANDU plan is actually quite brilliant. They are put in a protected ring near Yucca mountain. CANDU reactors can burn high-level waste from other reactors, so they could act as a further reprocessing facility for waste from other reactors. Water is piped from Lake Mead or other large body, and turned into Hydrogen through electrolysis. The byproduct of that is heavy water, and by happy coincidence CANDU reactors use heavy water as a coolant and moderator. So the overall fuel cycle cost goes down. Hydrogen is then pumped by pipeline from there to the power companies which could either sell it to power vehicles or burn it themselves for city generators and heavy industry.

Pretty cool concept. Doesn't have a snowball's chance in hell, because it would be politically unacceptable.
  #12  
Old 10-01-2002, 12:41 AM
Sam Stone Sam Stone is offline
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Hydrogen is an explosive gas. Gasoline mostly stays liquid. Big difference.

As for hydrogen heating when it is expanded, this is what I was thinking of:

Quote:
The gas may be either heated or cooled by the expansion, depending upon the initial temperature and the particular gas. For most gases at room temperature, expansion results in cooling, as anyone who has used an aerosol can or operated a carbon dioxide fire extinguisher has experienced. Compressed air initially at 273 K, for example, will drop about 1/4 K for each atmosphere drop in pressure, while carbon dioxide will drop 11/2 K for each atmosphere drop in pressure. The temperature below which an expansion produces cooling is called the inversion temperature; it is high for most gases, but for hydrogen, it is about 193 K. Hydrogen, therefore, must be cooled below this temperature before it is expanded.
Cite: http://www.hq.nasa.gov/office/pao/Hi...404/app-a1.htm

The 174 CANDU plan is actually quite brilliant. They are put in a protected ring near Yucca mountain. CANDU reactors can burn high-level waste from other reactors, so they could act as a further reprocessing facility for waste from other reactors. Water is piped from Lake Mead or other large body, and turned into Hydrogen through electrolysis. The byproduct of that is heavy water, and by happy coincidence CANDU reactors use heavy water as a coolant and moderator. So the overall fuel cycle cost goes down. Hydrogen is then pumped by pipeline from there to the power companies which could either sell it to power vehicles or burn it themselves for city generators and heavy industry.

Pretty cool concept. Doesn't have a snowball's chance in hell, because it would be politically unacceptable.
  #13  
Old 10-01-2002, 01:34 AM
Sam Stone Sam Stone is offline
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Hydrogen is an explosive gas. Gasoline mostly stays liquid. Big difference.

As for hydrogen heating when it is expanded, this is what I was thinking of:

Quote:
The gas may be either heated or cooled by the expansion, depending upon the initial temperature and the particular gas. For most gases at room temperature, expansion results in cooling, as anyone who has used an aerosol can or operated a carbon dioxide fire extinguisher has experienced. Compressed air initially at 273 K, for example, will drop about 1/4 K for each atmosphere drop in pressure, while carbon dioxide will drop 11/2 K for each atmosphere drop in pressure. The temperature below which an expansion produces cooling is called the inversion temperature; it is high for most gases, but for hydrogen, it is about 193 K. Hydrogen, therefore, must be cooled below this temperature before it is expanded.
Cite: http://www.hq.nasa.gov/office/pao/Hi...404/app-a1.htm

The 174 CANDU plan is actually quite brilliant. They are put in a protected ring near Yucca mountain. CANDU reactors can burn high-level waste from other reactors, so they could act as a further reprocessing facility for waste from other reactors. Water is piped from Lake Mead or other large body, and turned into Hydrogen through electrolysis. The byproduct of that is heavy water, and by happy coincidence CANDU reactors use heavy water as a coolant and moderator. So the overall fuel cycle cost goes down. Hydrogen is then pumped by pipeline from there to the power companies which could either sell it to power vehicles or burn it themselves for city generators and heavy industry.

Pretty cool concept. Doesn't have a snowball's chance in hell, because it would be politically unacceptable.
  #14  
Old 10-01-2002, 01:52 AM
Snugglebear Snugglebear is offline
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There has been a discussion of fuel cell cars in this thread that also deals with the danger of hydrogen explosions.
  #15  
Old 10-01-2002, 02:27 AM
Wikkit Wikkit is offline
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Quote:
Originally posted by scr4
How is it worse than a leaky gasoline tank?
The flammable range of Hydrogen is something like 4.1%-74%1 in air by volume. That huge range means that pretty much any concentration of it in air is explosive. Gasoline is only 1.4%-4.6%2. Add to that the already mentioned fact that Hydrogen is a gas at room temp, whereas gasoline is a liquid. Hydrogen is also odorless, so you're not going to know you're about to blow yourself up with that cigarette.

Then there's Hydrogen's ability to leak through metal tanks and weaken metals, crygenics vs. high pressures, and so on. It looks like the only safe way to do it is to store it in another chemical, as another dangerous gas, acetylene, is stored.


1 C. Borusbay and T. Nejat Veziroglu, “Hydrogen as a Fuel for Spark Ignition Engines,” Alternative Energy Sources VIII, Volume 2, Research and Development (New York: Hemisphere
Publishing Corporation, 1989), pp. 559-560.
2 “Alcohols: A Technical Assessment of Their Application as Motor Fuels,” API Publication No. 4261, July 1976.
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Old 10-01-2002, 09:02 AM
Mac Guffin Mac Guffin is offline
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Sam, also keep this in mind when comparing a gasoline leak and a hydrogen leak.

Gasoline vapor is heavier than air. It tends to sink and pool into low lying areas. Gasoline may be a liquid, but it vaporizes easily. Hydrogen, otoh, is lighter than air. It will tend to rise, and escape into the atmosphere, thus diluting it and rendering it harmless. The chances of a low layer of gasoline vapor finding an ignition source, say a spark or pilot light, would be much greater than that of the rapidly rising and dissapating hydrogen vapor.

By the time a high pressure Hydrogen tank reached the "inversion" temperature, most of the explosive gas would have risen away from the potential heat source. Whereas the next time someone drove a car with a backfire into the clinging gasoline vapor.....Boom!
  #17  
Old 10-01-2002, 01:02 PM
Mr. Miskatonic Mr. Miskatonic is offline
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I didn't have much to add, I just feel that everyone should buy one of these to play with.
  #18  
Old 10-01-2002, 03:36 PM
Jdeforrest Jdeforrest is offline
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A bunch of PSU students apparently solved some of these problems:

Link
__________________
"The greatest trick the devil ever pulled was convincing the world he didn't exist." - The Usual Suspects
  #19  
Old 10-01-2002, 06:36 PM
Strainger Strainger is offline
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One thing I notice in Jdefforest's link:
Quote:
For a fuel cell to work, the hydrogen must be ultra pure.
is in direct conflict with what I've found here:
Quote:
As long as there is a constant source of fuel – usually natural gas for the hydrogen and air for the oxygen – fuel cells will generate electricity.
(my bold)

From what I've been told by the Power Systems group where I work (they're heavily involved with the development of fuel cell technology), the second quote is more accurate. (Not only is natural gas less explosive, I believe it's also cheaper.) I'll ask them about it though. My original answer was going to be "they use natural gas instead of pure hydrogen" until I read the article about the PSU students.
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