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Renewable Energy Concept - Stirling Engine Composting

  1. May 28, 2017 #1
    So I've got this crazy idea. To put it simply, to use the heat from anaerobic composting to power hot-air engine, specifically a Stirling Engine.

    Based solely on my own reading, the center of a closed composting heap can reach anywhere from 120-160 degrees without killing the microorganisms required to produce methane. By water cooling the cold side of an engine, a temperature differential of >100F.

    I imagine a gamma configuration with opposed/linear cylinders: hot cylinder down, cold cylinder up out of the heap. Compressed helium as the working gas will increase efficiency. And a properly built Stirling Engine requires a regenerator to further increase efficiency.

    I'm the guy with the ideas, but I don't know how to do the complex gas equations, cylinder computations, electrical computations and etc. required to calculate the dimensions. As well as the necessary torque to run, say, an alternator.

    Trying to upload concept sketches.
    Any help would be much appreciated!

    Attached Files:

  2. jcsd
  3. May 29, 2017 #2


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    Try working out how much power you can extract from a compost heap first. The simplest way would be to push some copper pipe through it and run some water through. You would need to know the flow rate and the temperature of the water going in and out. Leave it going for a few days to check you are measuring the long term rate.

    Power = SHC * flow rate * (Tout - Tin)
    where SHC is the specific heat capacity of water.

    It might be better to use the hot water directly to heat your house/shower. Perhaps see..
  4. May 29, 2017 #3


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    According to Google, compost generates heat at about 275 watts per cubic meter.

    The other thing it generates is methane, which is already done on an industrial scale in landfills and sewage treatment plants. Usually, they just use the reactor heat to keep the waste warm for the microbes to do their jobs. If you cool it, you will at least need to insulate it to keep it warm.
    Last edited: May 29, 2017
  5. May 30, 2017 #4
    Thanks for the replies, y'all. I'll extrapolate and ask a few more things when I can. Thanks again.
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