Cone Pit Biochar in 15 minutes

We wondered, before going to the expense of building a steel wok like they use in Japan or at BlueSky or Zanjabil (estimated about $400 in costs to fabricate), what if we build a pit like Josiah Hunt but shape it like a cone kiln and use the type of layering technique that Michael Wittner demonstrated?

That was our experiment, which we are calling Cone Pit method. We dug a cone-shaped pit — 54″ top diameter, 24″ bottom diameter, and 16″ deep. The burn began with a single match and some cardboard boxes, along with a few small, very dry bamboo sticks. Within a few minutes it had grown to fill the bottom of the pit and we quickly started adding more and bigger bamboo to the fire. We watched for signs of it going white — indicating ash formation, and then we would throw on another layer of bamboo.

If we had more bamboo we could have probably made 10 times what we did, but we started with about 12 cubic feet of loosely piled dry bamboo and we used that in the course of the 12 minute burn. Then, with no more fuel, we started quenching at the edges and anywhere we saw white ash, and gradually worked the spray toward the center, ending the process after approximately 15 minutes. We quenched the fire thoroughly, left it out in the overnight rain, and then allowed it to drain into the ground for a full day before collecting and weighing what we had. It was 30 pounds dry weight (13.6 kg), about 7 gallons by volume.
Had to update the May 10 version of this with some missing credits so this is version 2. When we updated we lost 2 likes and 84 viewers from the view tally.

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