the single most important question for any alternate-fuel ships?

Discussion in 'Boat Design' started by ijason, Jan 28, 2009.

  1. 2farnorth
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    2farnorth Junior Member

    You are exactly right. However if my car breaks down I just get on my cell and call the tow truck. I dont have to know how anything works except the gas fill. Now if I am somewhere between california and hawaii.....I realize it is just my personal preference to be able to fix anything I own not because I am an egomaniac, because I am cheap. I do appreciate a good debate like you guys are engaged in. Maybe I am just jealous because I dont understand the whole water to electricity thing.
     
  2. robherc
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    robherc Designer/Hobbyist

    Hmmmm... maybe I can help a little there with an illustration (verbal):

    Stage 1: Power generation
    Some mechanical means of generating the electricity in the first place (whatever it is, they're all pretty similar to your car's alternator...unless they're solar cells)...check voltages to identify problems here, clean contacts as first step to correct them.

    Stage 2: Electrolysis
    2 Electrodes immersed in water. Hydrogen bubbles form around one, Oxygen bubbles form around the other.
    Check to ensure that bubbles are still forming & rising to the surface to identify problems here. Check voltage & visually inspect for corrosion on the electrodes to find possible failure points. Clean & tighten terminals, and clean corrosion off of electrodes to repair.

    Stage 3: Compression and Storage
    Some form of pumping mechanism (Re: AC compressor in your car) compresses Hydrogen into storage tanks.
    Check tank pressure levels to identify problems here. Check for leaks & check voltages to compressor. Possible repairs may include leak repair, compressor terminal cleaning, or compressor replacement.

    Stage 4: Fuel-Cell
    This thing uses a chemical process (that, honestly, I don't very well understand myself) to combine your compresses Hydrogen and Oxygen and create electricity.
    Check fuel pressures at inlet and electrical voltage output to identify problems here. If something goes wrong with the fuel cell itself (extremely rare), good luck fixing it...you'd have to be an accomplished scientist...lol (kinda like if you throw a piston/rod or crack a cylinder in your diesel/gasoline engine...you're screwed)

    Stage 5: Electric Motor
    I'm not going to insult your intelligence by explaining this...I'm sure you already know ;)


    ...Does that clarify/simplify the whole process a little for you?
     
  3. venomousbird
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    venomousbird Junior Member

    I agree, the technology behind fuel cells, electrolysis, metal hydride storage media, etc seem daunting at first, but operation of them if they are well designed can be made simple. Think about the level of complexity involved in making a PC (let alone the internet) work. But once you get used to how it all works together, and understand the basic function of all components it's not that big of a deal.
     
  4. 2farnorth
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    2farnorth Junior Member

    Now that you put it that way.... Not as bad as I thought. See, I risked looking like an idiot and actually learned something. :) The cold weather up here numbs the brain a bit, and beer doesnt thaw it out very well, though I try and try.
     
  5. robherc
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    robherc Designer/Hobbyist

    2far:
    Glad I could help
     
  6. Tcubed
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    Tcubed Boat Designer

  7. ijason
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    ijason Junior Member

    @2farnorth. rob did a great job of summing up the seemingly complicated process that we've all been jabbering on about. i'd like to ad a bit more to his neatly condensed post.

    i completely understand where you're coming from, of wanting to be able to turn the wrench yourself - and while at sea - to any vital component that fails, so that you can make it back to port, or at least keep pointed in the right direction until help comes. that's almost the same goal as my original question... i want to be able to be self reliant not just if something fails, but for the fuel needs for my ship, entirely.

    i think we've had good observation that sails offer the most traditional and universally available solution for free fuel sailing. but my biggest concern with sails is - as it has been pointed out - they generally require more hands to work them, for a larger boat. and you're limited to the weather, for when and where you go.

    hydrogen seems to be a very logical fuel for a boat. you're surrounded by the stuff, both in the air and the water, and it stores well and packs a bunch of energy. so if we can find the puzzle pieces for a system that can harvest and store it, in volume and time-line that is sufficient, using wind or solar based power, then you end up being able to rely on a simple electric motor to drive your boat.

    all in all, a boat relying on solar/wind powered electrolysis, some type of energy-efficient compression method, and a fuel-cell powering an electric motor is going to be MUCH more mechanically simple than any power cruiser. photo-voltaic cells, hydrolysis equipment, and fuel-cells have no moving parts! electric motors operate much more reliably than IC engine do. the weakest links in the system would be the mechanical rotor - if used - and the compressor for the hydrogen. both of those components are likely to be small enough to be able to easily stow replacements for both!
     
  8. ijason
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    ijason Junior Member

    what about steam engines?

    it was suggested earlier in the thread, the possibility of burning h1/o2 directly in an IC engine, along with an understatement of the difficulties of doing so. but i think it may be a great concept.

    what if you electrolysed h1/o2 from sea-water, compressed the same into tanks for storage, then burned the same - in conjunction with a solar pre-heater - in a boiler to produce steam at pressure?

    this steam could be used in an engine similar to this : http://www.greensteamengine.com/
     
  9. marshmat
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    marshmat Senior Member

    An interesting concept, ijason.

    The problem, just like when burning hydrogen in an IC engine, is the low efficiency of such a process. The Carnot limit for a system driven with 400 deg.C steam is about 57% thermal efficiency, and in practice you can rarely extract more than half that at best. Using solar collectors would give you a bit of extra "free" heat input, but you'd be hard pressed to fit enough of them on a boat to power it this way.

    That's not to say steam turbines don't have a place on a hydrogen-powered ship. A boat wouldn't be using car-like PEMFC modules, it'd be using the constant-load types: solid oxide, molten carbonate, etc. The exhaust steam from these things can be in the ballpark of 800 C- thus, in theory, a steam engine could recover up to about 73% of the energy that's left in the exhaust of the fuel cell. In practice it would be closer to 30-35%. But even so, think about what would happen to your fuel bill if you set up a fuel cell rig that extracts 50% of the chemical energy from the fuel, and then a steam turbine that gets 35% of what's left over. That's about 70% of your fuel bill going into useful energy- so your choice of double the range, or half the fuel costs, compared to burning that hydrogen in an engine.

    Now, granted, such a system would not come with a friendly capital cost.

    Fuel cell durability is not yet up to the standards of the IC engine. However, there is no fundamental reason why this problem cannot be addressed.

    On the motors side, I must admit there is something very appealing about a motor with only one moving part. Well-built electric motors routinely run for 50 years or more with no major repairs.

    The control circuitry can be a bit of a weakness. Right now, controllers are generally sealed boxes that can only be repaired by technicians trained by their designer. They are loaded with solid-state relays and FETs that depend on a microscopic junction layer to control hundreds of amperes (not to mention a couple of really, really big capacitors); when things break, they're not easily fixed. If someone were to come up with a modular, expandable controller that could handle a range of DC motor types, and whose component modules could be easily swapped out by the user if they fail.....
     
  10. ijason
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    ijason Junior Member

    @marsh. do you think you could re-use waste heat from the boiler and steam engine to pre-heat the incoming water? surely a purpose designed boiler would be quite efficient at using its heat to produce steam. or do you mean that a gaseous h1/o2 flame is not a very .... powerful source to try and warm up a big boiler? how many btu's per pound in h1/o2 mix VS propane? is one drastically more than the other?

    i'm entirely unfamiliar with the Carnot limit, but i am fairly certain you wouldn't need steam to be at quite that high (400C) a temperature to run a steam engine similar to the one i linked. the inventor has a system which uses a pressure cooker to produce the steam needed to run an engine. pressure-cookers top out at about 18psi, and their internal temps generally don't exceed 300F, to my recollection.

    the other option is to forgo the electric motor and have your propeller driven directly by the steam engine itself, which may yield better efficiency because you're not making/storing/converting/using energy, but just turning the steam pressure into rotational force.

    of course, another advantage would be that you get pure h2o as a precipitant when you cool the steam to recover its heat. :)
     
  11. robherc
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    robherc Designer/Hobbyist

    @ijason:

    1: Yes, you CAN recycle the heat using one of many types of heat-exchangers, but then you're adding a lot of weight...not the intent here.

    2: In practice, the hotter (ant thus, higher-pressure) a steam turbine is run, the more efficient it can become.

    So, the steam "topping-cycle" fuel cell would still be far more efficient than a direct steam engine heated by H2+O2 combustion (yes, Hydrogen pairs to create molecules...need 2 electrons to fill the S orbit).
     
  12. marshmat
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    marshmat Senior Member

    ijason,

    The Carnot limit is:
    1 - (Tcold / Thot)
    It represents the absolute maximum efficiency of a heat engine of any kind- IC, steam, turbine, whatever.
    Engines working on the Carnot or Stirling cycles can, theoretically, reach this maximum efficiency, but in practice it cannot be done, for a number of reasons. Other cycles- the Otto or Diesel cycles for IC, the Brayton for a gas turbine, etc.- have their own limiting efficiencies, which are always lower than Carnot.

    It's easy to make a boiler that is 90% efficient- heat is the desired output, not mechanical energy. But the engine or turbine that converts the resulting steam into motion, even if it is a "perfect" engine, must always lose a significant amount of that energy, in the form of waste heat.

    Yep, there could be very substantial efficiency improvements with such a system. It'd be bulky, of course, but that's not as big a problem on a ship as it is with a car.

    Don't get me started on the bonding configurations of hydrogen! (Those who have taken a few courses in quantum mechanics will know why it's not a good idea to start talking about that sort of thing! ;) )
     
  13. robherc
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    robherc Designer/Hobbyist

    Actually, you could use a (relatively) very small/light turbine for the topping cycle Matt...you'd just have to run it at higher RPM (which is FAR easier in turbines than in IC engines!).
    Just a note...other than that, I agree with you for the most part. :)
     
  14. venomousbird
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    venomousbird Junior Member

    I wrote a previous thread that didn't get any responses, but I was reading once about an invention that apparently used superheated steam in a ramjet style configuration, with no moving parts. The steam was injected at high pressure into a cavity, and the claim was that it caused some sort of reaction with the surrounding cold water that produced a lot of thrust. I forget the efficiency they were claiming, but remember that it was a lot higher than in any other sort of conventional engine.
     

  15. robherc
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    robherc Designer/Hobbyist

    I guess, in theory, if you superheated the steam enough you could boil the surrounding cold water in a controlled area (expansion nozzle) and create a good deal of thrust that way. I'm really not seeing that being a very high-efficiency method though, as you're wasting a LOT of energy on heating all that water to 100C. Maybe there was some other principle they were counting on?
     
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