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trpnbils

Biochar stove question

trpnbils
9 years ago

I've been using the Toucan TLUD (1 gallon) design for awhile now and wanted something bigger, so I started from scratch using a 20 gallon galvanized trash can as my burner. For the "crown" section I used an inverted 3 gallon galvanized livestock water dish with a 3" hole in the center and an 8"x2' chimney. There are about 50 or so half-inch holes in the bottom of the garbage can, and a dozen or so in the crown.

I did two burns today and the first burned out after the top 6" charred, and the second one burned REAL SLOW, but eventually did get to the bottom, although it wasn't an even burn and I still had some raw wood left. I'm chalking that up to poor choice in fuel. Not all of it was the same diameter...it ranged from chunks of bark to 4" or so diameter by 2' length logs. In general, I got little ash and more char from the second burn than I've gotten from all of my runs with the 1 gallon TLUD combined, but it was a SLOW burn and it was VERY smokey. Several times I thought it was going to go out. I never did get the "rocket effect" of flames coming out of the chimney like I did with the small version.

I know smoke can indicate too much air or not enough air, and I'm inclined to believe that this is not enough air. With the lack of large flame, slow burn time, and smoke, does that sound right? If so, would it make more sense to put more ventilation holes in the bottom of the trash can, in the crown area, or both?

UPDATE:

Okay - second run of the stove, and the results were worse with smaller fuel. I filled it with finger-diameter sticks from top to bottom, lit it up, and it burned great on one side (maybe too fast, even) but didn't burn evenly so the whole other side was basically untouched. The whole thing was REALLY smokey this time, but I have an observation:

It burns great without the crown part or chimney (so it's essentially a campfire in a garbage can), but as soon as I put the crown on (with or without the chimney) it would totally kill it. If I took the chimney off and lifted the crown part up an inch or so, it burst back into flames with no problem. To me, this indicates not enough air flow.... should I enlarge the hole in the top of the crown area? The whole top of the crown is about 15" wide, and the hole is approximately 3" in diameter. The other holes in the sides of the crown (10 of them) are 1/2" in diameter. Maybe more of them? Looking at the Toucan TLUD design, the crown is very open for its size and mine is not.

Thoughts?

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