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The Physics of the Hydrogen Economy
Spy der Mann writes "A Physics Today article entitled The Hydrogen Economy explores the possibility of using hydrogen as an energy source. The article explores the current methods, limitations, and the need for more research. For those wanting to point out the Hindenburg incident, the article doesn't talk about gaseous hydrogen only, but also about hydrogen fuel cells. My favorite quote: 'The natural world began forming its own hydrogen economy 3 billion years ago, when it developed photosynthesis to convert CO2, water, and sunlight into hydrogen and oxygen'. Interesting read for eco-fans."
A friend and coworker was describing a scene he witnessed at a plant that liquifies gasses. You figure out which one.
One of his coworkers was pushing a metal cart loaded with a test rig down an aisle. About halfway down there was a huge *whump* that echoed down the hall and the entire front half of the cart was in flames. The man wasn't seriously injured, even being so close to a tremendous fire.
A H2 pipeline had ruptured (H2 embrittlement I think he said) and was spewing a steady stream of the material in a jet across the walkway. Somehow it had caught fire and, since H2 burns colorless no one saw it.
Had that cart not been there.... ouch.
Is it just me, or should there be a distinction between "energy source" and "fuel?" If you burn gasoline, hydrogen is still the component providing the energy. So talking about using pure hydrogen versus hydrogen bound up with carbon (and other atoms) is a difference in fuel makeup than the energy source.
Or so it seems to me...
The Spoon
Updated 6/28/2011
Biodiesel, anyway you look at it, is indirect solar energy.(The same could be said for fossil fuels, but it's billions of years of built up solar energy) Moreover, if demand increases, the components will become more sparse and expensive.
IIRC, there was an article a while ago about how someone was making biodiesel for something like $0.30 a gallon, but he was getting all kinds of used resturaunt fat for free- and it wouldn't be free for very long if it becomes an ingredient in widely used fuel.
Moreover, for the part of it that is directly plant based, we already use tremendous amounts of water to make the food we eat, and adding all the farms required to make any substantial amount of biodiesel would use up an incredible amount of water.
As far as I can tell, biodiesel is a novel and sometimes cheap form of fuel for a few hobbyists. Given what's needed to make biodiesel, however, I don't see how it could ever approach being even 1% of the fuel we use nationwide.
Alcohol, Tobacco and Firearms should be the name of a store, not a government agency.
Hydrogen is a Boondoggle. The energy density is so low, that we might as well use batteries if we're going to power vehicles with it. (It may be good for stationary purposes.) If we really wanted to, we could convert all US vehicles to diesel, and run them all with Algae-Derived Biodiesel using sewage as a feedstock. Because of the greater efficiency of algae, supplying all of our vehicular needs is actually feasible.
This would alleviate both the global warming problem and our dependence on Middle-Eastern petroleum. The technology is available now, and because of the high energy density, no sacrifices on the part of automotive consumers are required in terms of range and performance. (We may need to invest in research into better catalytic converters and turbocharging technology.)
regarding this comment about biodiesel: ... ...
"I don't see how it could ever approach being even 1% of the fuel we use nationwide."
don't forget the algae potential. per this UNH study http://www.unh.edu/p2/biodiesel/article_alge.html about10 million acres would be required for our usage, which is ~1/40th of our current crop farming space.
1. Huge vast amounts of Free Energy, courtesy of plate tectonics.
2. They are completely surrounded by all the water they could ever want.
All you have to do is drill down to the heat, use it to boil water to spin turbines, which then make electricity to crack the water to make the hydrogen. Done.
You heard it hear first. The amount of energy under Iceland and the Big Island is *insane*. Another good place to drill for heat would be the supervolcano at Yellowstone. Use the electricity generated there and you can pump in the water from most anywhere and crack it into H2. Also: by draining off some of the heat from the supervolcano, we might be able to prevent (or slow) the eventual eruption of that sucker.
Problem solved. Next?
HW
Shoes for Industry. Shoes for the Dead.
All of these discussions on novel means of energy production are well and good -- hydrogen, wind, solar, and several other approaches are quite promising. What seems invariably to be forgotten is that entropy, chiefly in the form of waste heat, is a limiting factor.
The executive summary version of this fact is that if the entire population of the earth were consuming energy at the same rate as Americans, the atmosphere would be incandescent with waste heat.
The obvious consequence of this -- and something which rarely receives any exposure on Slashdot unless it involves white LEDs -- is that producing more energy is not a viable long term goal; only conserving energy is. Even were this not the case, the current growth rates for energy consumption would lead to the exhaustion of even uranium for fission in a relatively small number of generations.
Arguably, the worst thing that could happent to the human race would be the practical availability of an effectively unlimited source of power like fusion. If fusion power proved to be anywhere near as cheap as its proponents claim it would be, all economic incentive to reduce consumption (and therefore waste heat production) would be eliminated. While it would be theoretically possible to offset some of this by moving production offplanet, the economic barriers would be steep. Considering the reluctance of our species to deal with the current manmade environmental effects of industry, there is little reason to be optimistic.
Alternative energy proponents all too often sound as if they were discussing perpetual motion machines. It is not possible to escape the Second Law of Thermodynamics. Some machines are more efficient than others, to be sure, but there is a theoretical limit and it is not a generous one. Beyond that limit, which is seldom even approached, all you can do is shuffle the wastage around; you cannot eliminate it.
This is not something anyone likes to hear, and I suspect that is why it is so universally overlooked. There is a utopian vision shared by technologists and science fiction devotees (and I count myself in both camps) in which technology will someday give us everything we want. Unfortunately, "everything we want" violates the laws of thermodynamics, and those laws appear unlikely to be repealed.
Proud member of the Weirdo-American community.
the skin was tested to be more flammable than another design that was adopted for the rest of the fleet.
References on this point are not decisive. What is decisive is when you ignite a sample and see how slowly it burns.
Some dozens of other hydrogen filled airships burned catastrophically without benefit of this supposed legendary unique covering material. Even discounting those due to military action, a large proportion of all hydrogen filled airships burned catastrophically, while no helium filled airship ever burned catastrophically.
I'm afraid I've lost a lot of respect for RMI over the past five years. They know the truth about the energy resources situation, but their publications promote soothing, pernicious lies. Organizations that say "We have an energy crisis coming, and the only solution is radical efficiency combined with lifestyle change combined with shrinking the global economy to achieve a gradual Powerdown" get neither grant money nor political support. Organizations that say "We have an energy crisis coming, but our technical fixes will allow the status quo to continue" get both grants and political support. RMI has chosen to say the latter, even though they ought to know better. By promoting a 'technofix' approach and claiming it can solve the impending energy crisis (it can not), they do us all a grave dis-service. If one carefully examines the numbers regarding viable future energy use, the realworld choices become quite clear. The single biggest step our species MUST take, that hardly anyone is even willing to discuss, is removing cars from cities. I personally believe that any city which has not converted to a mostly carfree model by about 2020 will cease to function as a city. About 30% of the global energy budget is spent on moving big chunks of steel and small people around our cities. See http://www.carfree.com for a detailed and attractive explanation of why carfree cities would inprove urban quality of life while using drastically less energy. I hope we eventually all realize that it's how we should have done things in the first place.
First I want to thank you--that is a useful table!
(How do you prevent slashdot from sticking random spaces into the link?)
But please look at the right column!
in terms of _gravimetric_ density, hydrogen (in any form) beats every other entry handily. 39,000 Watt-hours/kilogram, versus just over a third of that for propane, and only 12,200 for gasoline. Gasoline wins on this table hands down for _volumetric_ efficiency, but you'd be hard put to show from that that carbon bond strength has anything to do with it at all. I think it is a simple matter of the material density. Unfortunately I don't know the chemical formula of propane, but a typical gasoline molecule is made up of roughly 2 hydrogens for every carbon, or maybe a bit less. A benzene ring has 6 and 6 but it is a closed system; to form the more complex hydrocarbons there clearly can be few double bonds involved and lots of hydrogen.
Let's just assume that gasoline is 1.5 hydrogens per carbon, and that how they are bonded to each other doesn't matter much--in the end it all burns to water and CO2. OK? Carbon weighs 12 AMU, plus 1.5 hydrogens gets us 13.5 versus 2 for a hydrogen molecule. Let's multiply the hydrocarbon by 4: we get a segment that weighs 54 with 4 carbons and 6 hydrogens, that consumes 11 oxygen atoms to yield 3 waters and 4 CO2 molecules. This fuel weighed 27 times one hydrogen so we burn 27 kg of it to get 329400 Wh/kg or 8.446 times the heat of burning 1 kg of hydrogen. Now subtract 3 from that output ratio, representing three water molecules, to get 5.446 and divide that by 4; the formation of 1 CO2 by these assumptions releases as much heat as 1.36 water molecules forming. Not a dramatic difference and I rather think that hydrocarbons have more hydrogen than that. Note that propane is more punchy on a mass basis and is a simpler, lighter, more hydrogen-intense molecule. If the hydrogen ratio was as low as 1:1 which I think is impossible for something as volatile as gasoline, forming CO2 would be worth 1.533 water-formations--still pretty lame when you consider that there are 2 oxygen atoms in the reaction! If the ratio is more like 2 H to 1 C, then the output ratio drops to 1.19. Hydrogen-oxygen bonds actually seem pretty strong!
For cars or boats or trains, perhaps this doesn't signify all that much; volumetric density matters a lot. But for aircraft, where saving weight is the name of the game, hydrogen fuel delivers tremendous advantages. Even though the fuel must be stored in very bulky tanks that will cause extra drag and increase structural weight, the savings in fuel weight would be so great that the wings (a major source of drag area!) would be much smaller. If anyone here cared I could go on about how the advantages for airships would be even more decisive.
It is very overblown then to claim that "hydrogen as a fuel is not backed up by the laws of physics." Where weight is important, it is three times better than any other chemical storage medium. This is why it is used in rockets of course. (Higher specific impulse too--but that is also a funtion of its very low mass and high _mass_ energy density!)
Evidently there is not all that much energy in the double bonds of carbon as you think.