Hydrogen as fuel

Discussion in 'General Science' started by Wendy, May 13, 2012.

  1. Wendy

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    Last edited: May 13, 2012
  2. nerdegutta

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    Link doesn't work... :(
     
  3. Wendy

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    Fixed.....
     
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  4. nsaspook

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    The problem with H2 production is it's not really a fuel but a storage technology like a battery. The energy conversion in the redox process even with a platinum catalyst is still less than a lead acid battery. A lost cost catalyst will reduce the starting cost of a module but the basic fact that it's not a primary fuel but only a way to transfer energy remains the same.

    http://www.kvab.be/Downloads/Lezingen/Hydrogen_energycarrier.pdf
     
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  5. Wendy

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    Right now all fuels are a storage medium, if looked on in that light. Fossil fuels are energy from the sun that have been stored for millions of years by nature. How fuels are made is quibbling, where they come from is not as important (other than the politics and climate science) as having the fuel to begin with.

    Hydrogen has a high energy density, much greater than a lead acid, so the comparison is not really valid. It is a true fuel, able to be stored as such and burned in conventional internal combustion engines, or used in fuel cells for electric vehicles. There are many problems that will need to be solved with storage and whatnot, but they are not insurmountable, merely technical. Most important, it is closed cycle, you do not need to burn fossil fuels to use it. It can be made many ways, and is reasonably portable.

    Ideally, if we could make gasoline from atmospheric CO2 and H2O that too would be closed cycle. Making hydrogen would still be part of the process though.

    The reason I pointed out the thread is it is a new process. Nature does the same thing with photosynthesis, using sunlight and water to break the bonds of water to make new chemicals, sugars. This is their fuel.

    I don't know how efficient the process is, if it gets close enough to unity (which it can never achieve) it will become a practical fuel, or a primary ingredient in making one.
     
    Last edited: May 13, 2012
  6. nsaspook

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    I wish it was merely a "technical problem" but almost everyone who has seriously looked at hydrogen as a "fuel" has decided it's thermodynamically inefficient and to just use the power directly as electrical energy for vehicles, etc... as the basic electrical infrastructure is already in place and to spend the 200 billion needed for hydrogen pipelines and storage instead on grid improvements and better batteries.

    http://www.efcf.com/reports/E04.pdf
     
  7. Wendy

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    I've seen that debate, it is not a settled issue as you would state. So far a lot of money is currently being spent by a lot of people that says otherwise.

    The only reason it is inefficient is the creation of it, not the use of it. It takes too much energy to make vs what you get back. It has greater energy density than gasoline when burning per weight. Storing it is a different issue. Again, there are processes that will split H20 that are more efficient, the link I provided is a new method. There are other ways that involve solar and PN junctions, but no direct electric current.

    By making broad declarations, you lock yourself into arguments that are not necessarily correct. I am not talking about thinking outside the box, too many people use that phrase to justify violating physics. I am talking about looking at what is in the box before rejecting it out of hand though. You seem stuck on fuel cells, which is only one application. An ICE can use it just fine as is.

    There is a very good reason it is a rocket fuel, it is that energy density I was mentioning. It is still #1 for those choices, including the hybrid ramjet engines, last I heard.
     
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  8. nsaspook

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    I did say almost everyone.:D But those who believe like I do include Steven Chu, (currently in control of public research funds) Obama's energy secretary. http://www.nobelprize.org/nobel_prizes/physics/laureates/1997/
    http://www.bloomberg.com/news/2011-...ilure-conceded-by-chu-paring-budget-cars.html

    I'm not stuck on fuel cells (or it's use in a ICE with poor efficiency) but currently that is the most efficient practical method of extracting the stored energy from the hydrogen carrier to generate electrical power and heat. I'm all for research (with private money) but the fundamental physics of hydrogen (poor round-trip efficiency) make it IMO a loser for energy storage, unless as Chu says four miracles happen.

    http://www.technologyreview.com/business/22651/page2/
     
  9. Wendy

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    Again, this is possibly subject to change. The end product, H2, is a fine fuel. I am not basing my opinions on anyone else, I formed them myself. The article I referred to did not mention efficiences, which was a flaw, but did state it was more effiecient. As with solar cells, slow incremental improvements could turn things around over time.

    As with graphine and other threads, I will use this one to document the slow incremental improvements, if there are any.
     
  10. THE_RB

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    Hydrogen is a good fuel it releases a lot of energy and can do it quite fast and at high temperatures. It is also good being an element it does not degrade over time and go off (or change characteristics) as many hydrocarbon fuels tend to do.

    However it is not easy to store with current technology being very bulky and requiring more energy for compression prior to storage. Hopefully some of the new work on storing hydrogen in metal substrates or other forms will be good, but I personally think the big breakthough will come with some discovery of how to turn the hydrogen into a liquid fuel like gasoline which can be transported, handled and used with the same ease.

    I really see that as the future vehicle energy system; renewable energy (solar etc) used to generate the hydrogen, then the hydrogen converted to a liquid fuel, then cars being fairly similar to what we already have (internal combustion) with some hybrid electric capability.
     
  11. DerStrom8

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    I've seen HHO generators get put on cars to boost gas mileage (it works in tandem with the gasoline), but I can't imagine it's all that efficient. It'll drain the battery that much faster (to create hydrogen from water), so you'd probably actually lose more money than you save, with that method anyway. I'm curious what technologies might pop up in the near future to make electrolysis (or other hydrogen-isolating method) more efficient.
     
  12. nsaspook

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    Most texts quote a maximum possible conversion efficiency of about 65% using electrolysis with pure water. (Bonding potential 1.23/1.90 Electrolysis potential)

    Burning the H2 production in a ICE will get you about 58% theoretical efficiency of that 65% or a 83% theoretical efficiency of that 65% for a fuel cell.

    That's without losses for compression and transport.
     
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  13. Wendy

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    Catalysts tend to be outside the rules, other than they still have to follow the rules of thermodynamics, and electrolysis is only one way of going about the goal. The photo type PN junctions used for hydrogen/oxygen separation are not electrolysis in the classic sense, and even if they are fairly inefficient sunlight is free.

    I think I mentioned I wished they had better numbers for efficiency. Maybe in the future...

    HHO generators, as proposed by their advocates, are a major violation of the rules of thermodynamics. By running lean the engine is getting greater fuel economy at the expense of the engine itself. The piper will be paid, one way or another.

    Add to the fact that any increase is not that great, I think I would put my money in better engineered cars.
     
  14. shortbus

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  15. t06afre

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    Actually it is done now. As one example biodiesel using vegetable oil. The plant will do the process you describe. Using the sun as energy source. Will this save the earth. Not very likely. I just mentioned it as an example.
     
  16. THE_RB

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    Slightly off topic but it's generally accepted that good farming land is best utilised for food growing, and energy harvesting from the sun etc is more effieiently done in areas of very high insolation and very poor soils etc (deserts) harvested directly with equipment and not needing to grow things as an intermediary step.

    Fortunately electricity is even easier to distribute than crops. ;)
     
  17. WBahn

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    It's a bit interesting that hydrogen is always touted at having (roughly) three times the energy density as gasoline, but it is seldom emphasized that this is on a per unit mass basis. However, especially for transportation purposes, while mass energy density is important, so is volumetric energy density. Even in liquid form, the volumetric energy density of hydrogen is about an order of magnitude less than gasoline. So, while the hydrogen in that tank in your little Mini Cooper will only weigh a third what the equivalent gasoline would weigh, it will take up ten times the space and require a tank that is a good fraction of the size of the entire car. If you go the route of using metal hydrides, you can get decent volumetric energy densities, but the mass energy density becomes worse than gasoline. Plus, they can require thousands of psi to get them to uptake the hydrogen and moderately high tempuratures to get them to release it (though I would think the latter wouldn't be a huge problem as you could hopefully use the waste heat of the engine).

    Also, my understanding is that hydrogen-powered internal combustion engines still have some serious materials properties issues such as crystallization of the combustion chambers. I haven't heard (or looked) for what the present status of this is for quite some time, so perhaps they have licked that problem using ceramic parts or some other approach.
     
  18. THE_RB

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    Yeah it's not an ideal fuel for internal combustion engines due to the fast burn times, high heats and reducing effects. But it's a great fuel for other things (like producing heat in general, or welding processes).

    I'm really hoping someone will find a way to make hydrogen into a stable liquid fuel, to make like a "synthetic gasoline". Ideally the liquid fuel would have addressed the problems with use in combustion engines. And may even be blendable then to extend real gasoline reserves.
     
  19. massive

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  20. THE_RB

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    Thanks for the link. :)

    From their technology page;
    [​IMG]
    http://airfuelsynthesis.com/technology.html

    It looks like they are using renewable energy and standard electrolysis to make H2, then renewable energy to extract the CO2 from air, then another process (that does not consume energy?) to convert H2 + CO2 into a hydrocarbon fuel.

    Are there any chemists here who could discuss that? And if the principles could be adapted to a low cost home setup?
     
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