The oxygen is very much reduced, but not cut off completely.
The early charcoal burners would carefully build a dome shaped densely
packed stack of suitable timber, and fire the core like you would a bonfire.
When it was well alight they would cover the entire dome with cut turf (sod
usa speak?) that had been damped down, leaving just a small hole in the
centre of the top for the steam and smoke. The art was in tending it to
keep the turfs sealing as they dried out, and knowing when to open up and
call it finished.
No doubt there are much more modern processes using steel reaction vessels
nowadays, but some is still made in the old way.
Bromley, Kent, UK
Good description. And some of us have been known to use scrap wood, and
old oil drums as "steel reaction vessels", which of course they _are_....
Whether you're doing the big earth mound or the oil drum method, expect to
lose the occasional batch until you get the hang of just when it's time to
cut off the air, or let it back in. Seal it too soon, and there won't be
enough heat to cook all the wood to charcoal; open it too soon, and you
get a big bonfire instead of a batch of charcoal.
The way I recall using a "steel reaction vessel" is pretty fool-proof -
fill that with the charcoal-to-be and toss it over a fire
(non-charcoal-to-be). You need a vent pipe so the thing won't blow up,
and a lot of what vents (after the water vapor) will burn, so you might
want to run that vent pipe down to the fire area (you might even put a
burner nozzle on it) for efficiency's sake. No need for any oxygen into
the drum at all.
This may not be how others do it, but I've seen it done this way, it
works, and it utterly removes any need for fiddly oxygen control (at the
cost of burning up some wood completely, on purpose). DWYL.
On 14 Oct 2003 01:38:35 GMT, email@example.com (HppynBP) wrote:
Probably not. Charcoal burners never seem to agree on this - some
reckon you need to control temperature, others that it's all about air
It will go out. When burning, a very small amount of air does get in.
Burning wood in a woodstove is a three stage process. Hot wood
releases "producer gas", a mixture of carbon monoxide, methane, steam,
acid vapour and several others. This gas burns in the stove or flue,
which is why woodstoves need to have large baffles to be efficient.
Finally the remaining charcoal (ideally pure carbon and a little inert
wood ash) is burned.
When burning charcoal, only the first process (the pyrolytic
distillation) is wanted. Some of the second (burning the gas) is
permitted, to keep the burn going. This is controlled by restricting
the air (which in turn keeps the temperature down). Keeping the
temperature down stops the final process, that of burning the
charcoal, from getting started. After a good burn, there should be
very little white wood ash formed.
If charcoal starts to burn in the mound, the temperature rises
rapidly. This may then accentuate a split (in an earth covered mound)
and the whole process "runs away". Quick action is needed to cool the
mound right down before allowing it to continue as normal.
Modern charcoal production on fixed sites uses a retort process,
either small portable retorts in an oven, batch tunnels containing
trolleys, or a continuous retort process (depending on the age of the
plant). The wood is sealed from all air supply and the heat is
applied from a separate fire. The gas produced may be used for part of
Die Gotterspammerung - Junkmail of the Gods
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