Okay, so I did another burn today in my second attempt to make biochar. I used the same system as before, but with only pine (to get the fire started) and oak, no brush.
It seemed to work better, and definitely produced less smoke and more heat. I could see smoke coming out from under the lid of the inner trash can and getting burned in the fire. Most of the initial charge of wood was used up after about 45 minutes, and I only added a little more oak.
I think the biggest problem is with the size of the barrels — I can’t fit enough wood in between them to make a fire that is long-lasting and hot enough (although I haven’t observed the results of today’s burn yet). I need either a larger outer barrel or a smaller inner barrel, or both. I don’t want to have to be standing around for hours feeding the fire one kindling-sized piece at a time.
Other things to do to improve this system: make more holes in the bottom of the large can, insulate the large can.
Other ideas: make a masonry enclosure for cooking/biochar production; make a rocket stove/biochar production system, perhaps based on that 10-gallon trash can.
Update: The results were, if anything, worse than the first time. I’m just not getting enough heat into the feedstock.
Ending and Beginning 
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