Interesting design, lots of clever ideas! I haul home chips from the city park to use in my compost pile, and usually pick out several wheelbarrow loads of thin branches, strips of bark, and some long stringy pieces. These all end up in the charcoal making barrel, usually at the very beginning when I am trying to build that char bed on top of the load.
Where do you get those large threaded nipples and caps like what you used for the fuel fill? What size are they?
Do you think those flue heat fins might choke the air flow somewhat, but I guess you are using some forced air coming in at the lower side of the retort.
I once tried an upper sealed retort over my lower barrel, supported by some 1/2" rebar, which got so hot it sagged. Even larger rebar deformed, too. My lower retort finished in the usual 90 minutes, but the upper retort needed 4 hours to make good bell-ringing charcoal, and not torrified wood. I eventually abandoned that plan.
"All that remains is to coat the lower water tank retort with 1 inch of 1 part cement/1 part lime/ 12 parts perlite insulating stucco plaster." Be sure to let us know how you install this plaster, and how well it holds up to the heat. My recent experiments with plaster/perlite/ground glass have been working well, but the mix is cast into a large round oil pan with a center hole, and acts as a cover for my large charcoal making TLUD stove, and a support for the bricks holding the pots. The plaster doesn't have much strength, so the steel pan keeps it from cracking. Also, I store it in the house, out of the rain, when not in use.
I just came in from making another barrel load of charcoal, with never even a whisp of smoke!
I am still using the method Gary Gilmore shows in his videos, and after 248 barrel loads, it works well. Here is a photo of the dirt around the bottom air holes. To dump this, I will remove the steel liners, and tip the barrel over.
It sure does look crude, compared to your system, and that of K. Van Looken.
Can't wait for the next update on your progress.