he author, Gary Gilmore, explains how he designed a charcoal retort from steel drums. This is a smoke free design also the flare could be put to use.
Charcoal by Gary Gilmore video 1
First make the retort by adding air holes to the bottom of a steel drum.
Then make the afterburner by turning another steel drum into a tube.
Then start loading the wood (no more than 20% moisture) tightly packed into the retort. (This contains a great description of wood as nature's battery).
Charcoal by Gary Gilmore video 2
Once you have the wood packed in the retort, build a small fire on the top. (There is a nice description of a top lit retort system). Once the small top fire has caught, ad the afterburner (the tube) to the top of the retort.