Vertical Pit Biochar Method

1. Pits and Trenches are cheap (labor but no cost).
2. Pits and Trenches reflect radiant heat back into the fuel.
3. Pit and Trench fires are easy to get close to and work around.
4. Once squelched, the biochar can be covered with earth and left - no handling.
5. Pit and Trench fired biochar processes with chimneys marry the efficiencies of both top-lit and rocket stove methods. (I am beginning to think that under the right conditions this represents efficiencies that play out on a microscopic level.)
6. Biochar smothers the biochar beneath it.
7. Biochar does not hold or conduct heat when not burning, therefore
8. Once squelched, the biochar is cool to touch, and
9. Squelching the biochar is only needed for the top layer (coals are alive only to a depth of 2 to 4 inches, the biochar under that is already smothered and cooling).
10. Biochar is a good (though burnable) insulator.
11. Earth is a fireproof and a good insulator once dry but also holds heat.

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(My other BioChar videos: https://richardhroth.blogspot.com/2020/01/mediocre-old-man-videos-library-of.html)
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This is a prototype using salvaged materials. I found the pipe at the local Habitat for Humanity's ReStore (https://www.habitat.org/restores) It came as a 3' section of double walled insulated pipe which puts it at an excellent height to put a grill over for cooking. The chimney came with a flange that extended the base diameter to 24". (Very near the diameter of a 55 gallon barrel or barrel lid.) The inner insulated pipe had a diameter of 10" (outside) 9" (inside), and the outer had a diameter of 12", but I have also used a 10 inch chimney pipe (also from the ReStore) in this pit that worked fine as well.
This video is of the 4th time I used this particular pit to make char. The hole is about 2.5' deep and about 14' to 16" diameter with a 45 degree angled trench to the bottom for feeding in the stick fuel. There is no reason why a pit, once full, needs to be emptied. The char in it can be covered with earth and left and another pit dug. I did do this on an open trench burn. (Find video links to open trench and follow up review several months later by clicking on my indexed videos above.)
After 3 to 4 hours of feeding the fire the pit is full to within 4 inches of the top and in this trial produced about 13 gallons of good char. The high flames are not typical of the majority of this burn and is a waste of good heat. I had been burning damp fuel and brush, some green, for the majority of the burn, which - after getting it started - worked well, but ended the burn with some dry 2" and 3" fuel and the high flames that could have been controlled by careful hand feeding.

Note that at the end of the video I squelched the char and within 60 seconds stuck my hand down into the char. The soil, because it holds heat, continued to steam for several minutes. I dug out the char from the pit two days later and under the surface of the char the soil was still warm to touch

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