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I wanted to experiment with making charcoal because I live on a large property, and the kiln method seemed to be a good way of making a large amount at once. I made mine from some 55 gallon barrels that would be insulated with a mixture of dirt and straw. I keep the dirt dry by putting a tarp over it.

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The only problem that I have is that it seems to only be making really dry, partially cooked firewood. There is some really nice charcoal that is being produced in the kiln, but it only seems to be on the top. 90% of it is uncooked.

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I figured that there wasn't enough convection going on, so I made a stand from aluminum so there could be airflow under the wood.

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The first batch that I ran is the same wood that I am trying to carbonize for the third batch. This morning after the third batch I opened up the kiln and most of the wood is still brown on the inside. After the first run, the wood was bone dry, so I have no idea why it isn't fully carbonized by now. The air seems to just make a straight line for the chimney on the bottom. It is completely sealed, has sufficient insulation, and I'm keeping a large fire in the combustion chamber. The smoke turns nearly clear and I seal it off. I would say that all three runs combined would amount to 12 hours total, so something is definitely wrong with the kiln's operation. Perhaps I should reduce the size of the chimney's opening so it doesn't have as strong of a draw. Would that allow the air to circulate more? Any ideas?

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Maybe choke down on the chimney after a couple of hours, or figure out a way to change the air flow through it. Looks like a great start.

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To make charcoal in a kiln by direct smolder, you typically want the fire to travel against the draft. This way the wood that has burnt to charcoal will not burn further, as all the oxygen is depleted behind the smoldering fire front.
So to use this design, I would take out the bottom grate, and light the fire at the chimney end. When the fire gets to the intake, you're done. It's probably going to take a long time- when I do a single vertical barrel it takes about 6 hrs.

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This kiln does not operate by directly burning the wood that you want to turn into charcoal. You keep a fire going in a separate section of the kiln, and the heat from the fire travels to the rest of the 2 and a half barrels. The area where the fire is kept is designed to eat up the oxygen before it gets to the hole at the top that connects the two chambers together.

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If I had to guess, I'd say you need to install some sort of baffle to better control the flow of heat through the kiln. Also I wonder if your insulation is efficient. Only other guess is fiddle with the size of your intake and chimney.

I assume you've already seen Dave J's site (islandblacksmith.ca) and followed his links, if not you should check it out.

I would be interested to hear your end results with this and the process you eventually decide on. Personally I have only ever used the reverse draft direct burn method and results are poor at best, would like to try the Japanese kiln at some point.

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I opened up the kiln today, and it seemed like more of the wood had turned into charcoal. What I did differently this time is that I stacked the wood much tighter, but still in a lattice so air could still pass through. It seemed like the new charcoal was still made of smaller widths. I recall that the smoke coming out at the time I sealed it off was a mix of clear and white, so the thicker pieces were probably still in the process of carbonizing. Even if the larger pieces were in the process of carbonizing, I still feel that it was too slow. I think that I should add to the chimney length to increase the draw. I can't increase the size of the combustion chamber, so it makes more sense to force more air in by increasing the draw speed. Opening the air intake holes would only let more oxygen into the charcoal chamber because it would be the same size fire with extra oxygen and nearly the same draw speed. The added draw speed will also make the fire much hotter, travel across faster, and burn faster, so maybe this will compensate for the extra 1.5 barrels added on from the original design.

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This kiln does not operate by directly burning the wood that you want to turn into charcoal. You keep a fire going in a separate section of the kiln, and the heat from the fire travels to the rest of the 2 and a half barrels. The area where the fire is kept is designed to eat up the oxygen before it gets to the hole at the top that connects the two chambers together.

Aahh, I could not see that in the photos. But if you can't get it to work as designed, the smolder can still be your ace in the hole.

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  • 1 month later...

I finally did it! After I put on a longer chimney, I ran it and got the same results as before; low temperatures that only create very brown wood. I then realized that everything needed to change because the kiln runs on a ratio. I opened up the air intake for the combustion chamber, ran it again, and it quickly turned the wood into perfect-looking charcoal! Now all I have to do is create a side-blown charcoal forge and hook up my fuigo.

 

The area I opened up:

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The smokestack:

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And the product!

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