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charcoal burn

Ryan Mooney

Ryan Mooney

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Finally got a chance to fire up the charcoal kiln I built some time back. It was dark by the time we closed it up so will probably have to wait until next weekend to see what's inside (it's at a friends property) which is kind of killing me with anticipation.

Loading it up, you can see the baffle that goes between the front and the wood leaning against it to the left. We used a mix of random shop off-cuts, cherry orchard branch trimmings, some maple scrap, and .. whatever that log we had was (elm I think).
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Fired up, took about 30 minutes to really start to draw good... I think if I'd started with a smaller fire further back in the firebox it would've gone a bit faster maybe..
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Smoking!
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I didn't get a picture of the final smoke, pretty much clear and would light with kind of a roar when a flaming stick was put into it, but the flue is to big to sustain top combustion because the gas was to diffuse.
 
So the fire actually feeds through the barrel?

Any risk of the wood in the barrel actually catching fire, or do you let it cook for a while then shut off all air to the barrel?

The other charcoal makers I've seen are basically starting a fire in a sealed vessel, then closing it up.

I'm not entirely clear on the whole process.
 
Rick Prosser said:
That design is a little different than mine. Is the damper a kind of one-way valve for the firebox?
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In lieu of a better explanation I present this crude drawing, basi1ally the baffle/damper is a deflector to keep the fire from directly entering the main chamber. The theory (yet to be entirely proven on this build..) is that the heat travels over but not so much the flames so it cooks the volatiles out. I think the thing we'll find is that either I sealed the edges of the baffle well enough with mud and it worked pretty well.. or I didn't.

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Brent Dowell said:
So the fire actually feeds through the barrel?
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Yes, but it has to go up and over the baffle so you don't get a LOT of direct flame into the main "cook box" area. Based on observation of the smoke I think it mostly worked pretty well as it went very cleanly and distinctly through the smoke phases (white = all water, yellow/yellow-green = water plus wood vinegar, blue = pyrolysis gasses, clear waves of heat = starting to burn/shut it down!).

Brent Dowell said:
Any risk of the wood in the barrel actually catching fire, or do you let it cook for a while then shut off all air to the barrel?
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Yeah, that's one concern.. Based on my reading if the baffle did it's job we're mostly ok, although some of the stuff near the top/front might be slightly over cooked. I biased against that a little by selectively choosing what size/type of wood I put where with the heavier/bigger stuff top front and the smaller stuff further back. So fingers crossed :)

Brent Dowell said:
The other charcoal makers I've seen are basically starting a fire in a sealed vessel, then closing it up.

I'm not entirely clear on the whole process.
Click to expand...

Well basically you have to cook off the volatile compounds.. then seal it to stop the charcoal from burning up. Separating the "fire" chamber from the charcoal chamber is nominally a bit more efficient as you're not burning the stuff that'll be charcoal. Hopefully more than a bit in our case as we were able to burn small scrap to small to really make decent charcoal for the fire part, and use the bigger more interesting bits in the kiln itself. The amount of wood we burned to fire the thing was actually pretty low although the question of overall efficiency remains.

There are of course a LOT of ways to do this, this happened to be something I could redneck together with $30 worth of parts in an afternoon with an angle grinder and buzz box mig.

My design is more or less based on this one: http://islandblacksmith.ca/2013/03/charcoal-kiln-v-3-0/

Although I buried the kiln which both made the build easier (rock chimney hehe) but also arguably is more efficient. I also sized it down to one barrel as I felt that his full barrerl firebox on the front was likely overkill. IMHO pretty proven by the burn rate I got based on the smoke, once this system starts to draw I think you could just build a fire beside it and it'd pull the flames in, really really strong draw. He undoubtedly had a better baffle build but we'll see how much that mattered.
 

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I see I also neglected to explain the spacers.. basically some heavy chunks of scrap iron to keep the charcoal-to-be off of the bottom of the barrel and improve heatflow/airflow.
 
Great success!

The burn had a yield of around 40lbs of charcoal and we didn't have a huge amount of shrinkage in the kiln.

A few observations
  • Well over half was super hard and "clinked" like glass when pulling it out. This is pretty indicative of good quality charcoal so very happy with that.
  • The hardwood pieces worked better than softwood overall (no surprise) but even the soft wood worked really well for the most part.
  • The smaller pieces of softwood seemed to make better charcoal than the large (up to maybe 1x1" by however long). I believe that this was largely due to moisture content and fact smaller wood dried better during the first part of the burn.
  • I think we could have cut back on the input fire (mostly) and shut down the kiln (less so) a few minutes earlier to improve quality (mostly) and yield a bit more.
  • There was basically zero ash, we had a small scoop shovel full of bit-to-small-to-BBQ that went on the garden but even they were pretty black & hard.
  • The only piece that was really undercooked was a piece of plywood that snuck in (I tried to not have any.. but..)
  • The handful of wormy (might have been ants.. lots of frass/holes anyway) didn't make the best charcoal, somewhat crumbly and more over cooked. Again no surprise but an interesting experiment. Also still very usable and close to as good as some commercial stuff I've bought so still a net win.
  • This is a GREAT way to use up orchard trimmings to small for the wood stove but big enough you feel guilty putting them on the burn pile.

Unearthing the beast.

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A peak inside, looking super good. It's not all ash, it's not brown uncooked wood..

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Some of the cherry tree trimmings from the farm, these look really really good imho.

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A sampling of pieces, most of the stuff looked pretty much like this.

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One of the larger softwood pieces, lots more voids and collapse with these. Still very usable but I think they'd have worked better if they were drier or smaller or both (but mostly drier).
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Brent Dowell said:
Love that red scooper duper you got there.
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I bought it at the farm supply, they sell them for picking up road apples from the horse stall... but I bought it for harvesting walnuts and chestnuts without having the bend over to pick through the grass :) It also worked super well for picking up the "big enough to be interesting" pieces of charcoal.
 
Ryan Mooney said:
I bought it at the farm supply, they sell them for picking up road apples from the horse stall... but I bought it for harvesting walnuts and chestnuts without having the bend over to pick through the grass :) It also worked super well for picking up the "big enough to be interesting" pieces of charcoal.
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The metal ones work great for forking mulch from truck to flower beds, too. I'd worry a bit about the possibility of picking up still hot charcoal bits with your plastic one, though.
 
Jim DeLaney said:
The metal ones work great for forking mulch from truck to flower beds, too. I'd worry a bit about the possibility of picking up still hot charcoal bits with your plastic one, though.
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If it had been within a couple of days, then yeah that would be a concern, but we were 6+ days after the burn so it seemed pretty safe. I also figure that if that's a problem then we're likely to quickly have a bigger one once we bag it :eek:
 
Strongly agree on the drier part. There was some very visible differences between the really dry stuff and pieces that had some retained moisture, the latter being measurably more crumbly. Even the "more wet than it ought to have been" was still reasonably usable but not nearly the same quality. This kiln seemed to do a pretty good job of drying the marginal stuff (not sure how well it would do with actually wet wood .. as we had a pretty wide mix of random bits), but the quality loss was noticeable for sure.
 
Well we tried another one today. Some slightly bigger chunks of 3 year dry oak (nothing over 4" across most 3" or smaller - various lengths).

We're not sure if it's the oak, the more consistently slightly larger sizes of the pieces, the fact the wood had been rained of for four days, the fact it was hovering around freezing out, the 30-40mph wind with sideways rain/occasional sleet.. or some other factor.. but we ran the thing for around 5 hours and it was still blowing wet "smoke" out so was pretty far from done. Tentatively I'm thinking we should have debarked the wet bark off of the wood and things would've gone quicker. So we shut it all down as it was heading on dark and the wind and snow had started to really kick up some plus everyone was kind of freezing. So we'll resume on a perhaps hopefully nicer day. The current theory is that we were still in the "drying out phase" so we ought to basically be able to leave it sealed until then, then just up up the fire box again and fire it up to finish. On the plus side? (tentatively) it looks like my latest score of oak limbs is enough wood for three maybe four more burns!!!

This burn also has a couple medium sized bundles of bones, I'm hopeful that it might hit the magical 500F long enough to char them into bone black for ink pigment.. as sort of another weird side project :cool:
 
So cool. I'm wondering about making maple charcoal. I've got a decent supply of maple firewood laying around now that I'll need to let dry out for a while.
 
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