Figured out a useful hydrogen fuel cell application

Discussion in 'Hydrogen fuel cell vehicles' started by bwilson4web, Nov 13, 2018.

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  1. bwilson4web

    bwilson4web Well-Known Member Subscriber

    Every year some family in Dixie will bring their portable generator inside for heat and light. The next day, they are dead from carbon monoxide. But a 1-2 kW, fuel cell generator would solve the problem:
    • light enough, 20-30 lbs, to roll or be carried in the house
    • hydride filled, low pressure tank, -10-15 lbs loaded
      • rechargeable at the local hydrogen supply
      • hydride storage may help purify the commercial hydrogen
    Bob Wilson
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  3. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    "Rechargeable at the local hydrogen supply"

    I guess you're talking about the sort of company that sells canisters of compressed gases. It's not like there are a lot of public H2 fueling stations nationwide. Outside California, those are pretty much limited to a couple of dozen fueling stations used to supply private fleets of H2-powered FCEVs.

    Hydride storage is an interesting solution, but it takes heat (and energy) to get the hydride to release the absorbed H2 gas. Therefore, that makes burning (well, oxidizing) H2 in a fuel cell even <i>more</i> energy inefficient than it already is.

  4. bwilson4web

    bwilson4web Well-Known Member Subscriber

    Many welding supply stores have hydrogen for specialized metals. Living in Huntsville AL, home to NASA Marshall Space Flight Center, we have a lot of rocket scientists.

    I figured the waste heat would be enough but I need to do a thermodynamic analysis. However, this may be a case where home electrolysis may work. Recharging the hydride is not time critical.

    Bob Wilson
  5. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    I don't know that much about using hydride for H2 storage; just a few articles I've read.

    Based on the limited amount I've read, it does seem that home generation of H2 might be more practical if you're using hydride storage. If my understanding is correct, that allows use of fairly low pressure, which would eliminate the need for expensive high-pressure pumps, as well as significantly reducing the lost energy from compression and loss during storage.

    Good point about recharging the hydride not being time-critical for use in a space heater. As I understand it, the slow absorption rate is what makes hydride storage a non-starter for FCEVs.

    Using kerosene (or gasoline) heaters for home heating also represents a serious safety hazard, again due to carbon monoxide emissions. So I'd be interested to see any thermodynamic analysis you'd care to perform.

    What I don't understand is why you'd want to use a fuel cell for the purpose. Is the idea to use H2 to generate electricity in a fuel cell, and use that electricity to power an electric heater? If so, that would be massively less energy-efficient than using electricity directly from the wall for the purpose.

    It might make sense to use that inside a car, where you can't just plug into the wall. But there, I wonder how much room such a unit would occupy, and how much it would weigh. A gasoline or kerosene cabin heater inside a car might represent a significant safety hazard, but at least it doesn't occupy that much space, and such heaters -- and their fuel -- are relatively inexpensive.

    Just now I exercised my Google-fu in looking for a modern replacement for the kerosene/gasoline space heater, but I didn't find anything that looks promising. I do see that modern units can (and should) have detectors for low oxygen level, but that's a completely separate issue from carbon monoxide (CO) buildup. There can be enough CO in the air to kill you even when there is plenty of oxygen present.
    Last edited: Nov 15, 2018
  6. bwilson4web

    bwilson4web Well-Known Member Subscriber

    To simplify the math, a 1 kW, fuel cell, 'generator' would have about 200-400 W waste heat. This means it needs ~ 1.2-1.4 kW of hydrogen. The thermodynamic analysis is how much heat is needed to release enough hydrogen for 1.2-1.4 kW of fuel cell output both electric, 1 kW, and hydride tank heating, 200-400 W heating. These are just my foggy memory of the actual energy flows. But I think you can see the direction I'm headed.

    What is less appreciated, a membrane fuel cell also makes an excellent (or should) electrolysis cell. So feeding grid power, slowly, with appropriate pressure management should recharge a hydride storage container. So in standby mode, it can be brought to ready for a 24-48 hour, heat and electricity source. It would also scale but that also includes weight and cost.

    Bob Wilson
    Last edited: Nov 15, 2018
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  8. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    Well of course, when it comes to a space heater, the "waste heat" is just as good for its purpose as heat deliberately generated! :) As has been pointed out, an electric heater is as close to 100% efficient to be indistinguishable from it, for all practical purposes.

    From an economic and practical viewpoint, the problem with inefficiency will come only with generating and storing the H2, not with any inefficiency in oxidizing it in a fuel cell. If the fuel cell is actually located inside the space you're trying to heat, then any heat generated by that fuel cell isn't wasted.

  9. bwilson4web

    bwilson4web Well-Known Member Subscriber

    They'll need a water catch pan (or dog water pan,) but otherwise, hazard free compared to the usual gas generators.

    Bob Wilson

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