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While doing research on various designs for charcoal retorts both on IFI and elsewhere, I ran across this interesting variation that I wanted to get folks' thoughts on. It's an indirect-method retort, but rather than a double-barrel design with the fire around the outside, it appears to be essentially a 55 gal drum with a rocket stove in the middle, fueled by the wood gasses being piped back in through the fresh air intake. Has anyone here ever seen/tried/used/built anything like this, and would they recommend it? On the face of it, it looks like it wouldn't be terribly complicated to build and wouldn't require quite as much firewood to get up to heat, especially if the outside is well-insulated. Thoughts? Addendum: another video from the same guy shows a similar retort that he build with bricks and clay, not even using a drum.
So, I've been trying for the longest time to make charcoal for a bloom. I figure I need about 150 lbs or so to do around 70 lbs of ore. Been trying a lot of different methods, indirect, semi-direct, and of course, the classic - direct. All attempts have been in a 55 gal drum. First go was indirect. Loaded the drum, carved a hole top and bottom to run a 6 inch stovepipe through, let it stick out the bottom, and put the whole thing over a shallow pit. Lit a fire in the pit and fed fuel down the stovepipe. Had holes in the stovepipe to vent gas. Mixed results. When it worked well, around 30-40 percent charcoal. Biggest mistake, as in all of these was having my chunks of wood too big. Lots of unburnt remnants. Got tired of it and tried putting a 30 gal can inside of same drum, upside down, with the outer drum. Sat on the ground, closing bottom hole. Long stovepipe for a chimney out the top, holes in the side for ventilation. Rarely worked, not enough space between the inner retort and the outer drum. When it did, maybe 25-30 percent, Only really charred where the wood sat on top of the retort. Latest attempts, direct method straight out of bushcraft magazine on youtube, and occaisonal semi-direct. New 55 gal drum with 7 - 2 inch holes in the bottom, place on blocks, start a fire, load with wood, prop open, then take off of blocks and seal after about an hour when smoke changes color. Varying from around 20-40 percent yield. The shorter the burn, the more yield so far. The internet reccomendation was around 3 hrs. Found out I don't end up with anything if I don't seal it after about 45 minutes to an hour. Also, retried indirect method, and elevated the the outer drum so the bottom hole was partially exposed. Worked much better, seemed to get more oxygen. Haven't opened it yet to see results, but much better burning in outer drum. Conclusions? Sealed retort is harder to do, but yields much better charcoal. Smells good, denser, lights easier, better texture, and less fines. Direct method more consistent, but lower yield and less density. Pine is lousy by itself, not dense enough, but if you mix it with hard woods, seems to get better results out of both woods. About 100 lbs right now, and maybe 20, 30 gallons to check on in morning. Advice? Comments?