Thursday, November 12, 2009

Heat from Composting Biomass

I've been collecting material on the idea of extracting heat from compost piles and adding it to this section...

At first, this was a "that's kind of interesting" idea to me, but it has become more and more of a "that might really work" sort of idea.

Basically these schemes (there are several shown) start with a carefully constructed, large pile of biomass.  The biomass heats up as it goes through the composting process.  Pipes running through the pile pick up heat which can be used for domestic water heating and/or space heating.  Some schemes simultaneously collect bio-gas, which can be used for cooking fuel or even running a vehicle or generator.

Marc's compost furnace under construction.

A lot of work was done on this in the 70's by Jean Pain in France.  The section has some good descriptions of Pain's work, including two newly added videos (thanks to Curbie for these).

Marc's compost furnace work is very interesting, and includes some results from his first winter of operation.

The MB-Soft work in this area is interesting, if a little hard to decipher.

The New Alchemy papers are also quite good.

The attraction of this approach to me is that it holds the promise of a carbon neutral way of generating useful amounts of heat over long periods of time.  Some of the Pain piles are said to have been still generating useful heat after 18 months.  It is quite a bit of work to build one of the structured compost piles and set up the heat extraction plumbing, but then you may be able to get useful heating from the pile for an entire heating season.
The efficiency is claimed to be of the same order as burning the biomass -- maybe even a little better.  In many cases, the biomass can be material that would just be left to rot in place.

Does anyone have more useful information on this area?
Any thoughts on how useful and idea this might be?



  1. Hi Gary,
    I've seen this idea a couple of times before. One important detail is that Jean Pain's setup does capture the bio-gas. If you don't any CO-2 reduction is probably going to be offset by the bio-gas, as it is much more potent as a GHG.
    By burning the bio-gas it's converted back into CO-2.
    What was really funny is the type of car Jean Pain used (Citro├źn 2-CV) to run on bio-gas. :-)
    Just my 2-cents,

  2. Hi Dimitry,
    Had not thought about the biogas emissions and how strong a GHG methane etc. are. But, would the same amount of biomass decaying in the field also emit the biogas? -- or not?
    Do you (or anyone) know of a good reference on composting chemistry, and what the products are as a function of the conditions under which the composting occurs?
    The field right next door to us was cut and baled earlier in the year. The small square bales are still just sitting in the field (now under more than a foot of snow). I am guessing that they could be mine for very little money -- wonder what kind of a compost heat generator they would make?
    Need to learn a lot more about this subject.

  3. Gary,
    I would be willing to bet any farmers/ranchers that have hay sitting like that would be more than willing to give it to you for you picking it up. They have to do it before the next growing season, and it isn't worth anything to them, despite all the money it took to make it. I see a lot over here in Washington, and even when I lived in Idaho that would go to waste. They put it into piles and burn it. There is the waste. Just think, if you had time to mosey around the area, you may find enough fuel to run one of these for free.


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