Charcoal

Tom,

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.

Andrew Mawson Bromley, Kent, UK

Yes there are more modern methods of making charcoal, this webpage has a nice way of doing it

Probably not. Charcoal burners never seem to agree on this - some reckon you need to control temperature, others that it's all about air supply

fire just go out and all

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 this.

-- Die Gotterspammerung - Junkmail of the Gods

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.

Conrad Hodson

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.