LPG or LNG engine on a tug boat - will it work?

Discussion in 'Inboards' started by yodani, Nov 10, 2014.

  1. AndySGray
    Joined: Jun 2014
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    Location: Cayman

    AndySGray Senior Member

    Look a little closer - it's a decimal point not a comma...

    a cubic meter of propane gas weighs under 2 kilo
    a cubic meter of air is a little over 1 kilo

    a cubic meter of liquid propane is almost half a ton (493 kilos)

    It boils at minus 42 degees (celcius) unless it is under pressure (the pressure of the propane gas above the liquid stops it boiling) - that is why your propane tank frosts up if you use for a long time - as you take gas away, the pressure reduces, the propane boils and takes heat from the liquid, dropping the temperature and causing the frost.

  2. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    "it's a decimal point not a comma..."
    Yes, I think here is my mistake. I have to ask Gonzo apologize, and I do, gladly.
  3. jmiele3
    Joined: Jan 2012
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    Location: Philippines

    jmiele3 Junior Member

    The biggest problem we have found is the lack of refueling infrastructure at most marinas. We have converted a few of our engines for CNG and LPG. These were converted for the offshore industry and must be intrinsically safe, as Gonzo mentioned. This is why "Do it yourself" types using the aftermarket conversion kits usually found for taxis are usually the ones who run into problems.

    These are some points / issues that we have encountered:

    1. Efficiency is lower. This means that you generally need to install larger tanks than with diesel. Sometimes much larger. Also keep in mind the fact that you can never run the tanks "empty". An extra 20% or so capacity is required for the fuel pressure.

    2. All gas is not created equal. In some regions the quality of LPG / CNG available is poor. Unlike with poor diesel, which results in clogged filters and such, poor gas means lower caloric output and higher consumption. For example, CNG available in Thailand is about 93% of the caloric output of CNG in Sweden.

    3. Refueling time is much longer. A 147 kg cylinder takes approximately 10 minutes. Multiply this by 10 or 15 cylinders. Something to keep in mind with commercial use.

    4. In some countries, fueling time is increased further by limitations on the lines used.

    5. Due to the lack of infrastructure, range becomes an issue. Diesel is everywhere. Gas is not.

    6. Conversion kits must only be used with engines that have modified pistons / cylinder heads.

    7. Depending on the location in the world, payback through fuel savings averages 3 - 4 years for commercial use (naturally, this can vary significantly). All bets are off on recreational use.
  4. yodani
    Joined: Nov 2010
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    Location: Danube Delta

    yodani Senior Member

    Good point John. I think the biggest impediment for this type of engines is infrastructure for refueling. If there would be as wide spread as the diesel the other problems would be minor.
  5. jmiele3
    Joined: Jan 2012
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    Location: Philippines

    jmiele3 Junior Member

    Indeed, Yodani. We are currently involved in a rail project and solving the infrastructure / refueling procedure is the biggest issue (we are designing tender cars for the rail carriages that will be swapped out at the destination, empty for full). The other problems can be solved through design, but procedural and infrastructure issues are far more complicated.

    On the marine projects, one was a crew boat (well-defined route) and the others were operating in harbors, so always close to a fuel supply. A tug in this situation, as long as intrinsically safe and well-ventilated, is certainly feasible if a fuel source is convenient.

    Cost wise, the converted engine adds approximately 30% to the price of diesel, with tank systems at least 100% more expensive than standard diesel tanks.

  6. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    Offshore suply vesels are now being built for gas where they supply fields that have gas. Offshore refuelling is coming.
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