Next time I am free I am going to pick up an old open top drum and cut it down so it fits like a cover on my fire pit wash machine drum.
I have thought about this a while.
After I am done with my fire for the sake of watching stuff burn I could stoke up the pit and smother it out with the drum.
It would not make charcoal, but I could cook a lot of the moister and impurities out of scrap.
I think they call this torrified wood.
Torrified fuel has some advantages like abnormally low moister content, it does not rot and insects do not like it,
If you made a simplified down draft gasifier for primarily burning charcoal it might also be able to handle a mixture of low grade charcoal and torrified wood without creating tar and moister.
Just a thought
Here is a wiki link that talks about Torrefaction.
Its claimed that you only lose about 10% of the energy stored in the fuel.
The down side to this is you are going to have left over pyrolysis products blowing out the sides of the drum
Since no one is around to observe the fire you can not safely light them and walk away ( fire haz )
Once these escape into the air you have odors that some people down wind find objectionable
Then there are the tars and condensate that will run down the inside of the drum.
These are not toxic waste but they are not good for the ground water and soil.
Ideally there should be a way to make a tar flare to burn these things, but then I come back to the issue of what to do about the fire I intended to smother out.
So the solution would seem to be some sort of collection system to capture the tar/wood vinegar and condensate.
Now I have a waste product to dispose of though since I have no use for this.
Oh ya the link