Renewable Energy Concept - Stirling Engine Composting

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SUMMARY

The discussion centers on utilizing heat generated from anaerobic composting to power a Stirling Engine, specifically in a gamma configuration with opposed/linear cylinders. The compost heap can reach temperatures between 120-160 degrees Fahrenheit, allowing for a temperature differential exceeding 100°F when water cooling is applied. The use of compressed helium as the working gas is proposed to enhance efficiency, alongside the necessity of a regenerator in the Stirling Engine design. Participants emphasize the importance of calculating power extraction from compost, suggesting a method involving copper pipes to measure water temperature changes and flow rates.

PREREQUISITES
  • Understanding of Stirling Engine mechanics and configurations
  • Knowledge of anaerobic composting processes and temperature dynamics
  • Familiarity with thermodynamics, specifically specific heat capacity (SHC)
  • Basic principles of power generation and electrical computations
NEXT STEPS
  • Research the design and efficiency of gamma Stirling Engines
  • Learn about anaerobic composting and its heat generation capabilities
  • Investigate methods for measuring water temperature and flow rates in compost systems
  • Explore the use of methane as a renewable energy source in composting
USEFUL FOR

This discussion is beneficial for renewable energy enthusiasts, engineers interested in thermodynamic systems, and individuals exploring innovative composting techniques for energy generation.

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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!
 

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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..
https://www.hindawi.com/journals/ijce/2010/627930/
 
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:
Thanks for the replies, y'all. I'll extrapolate and ask a few more things when I can. Thanks again.
 

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