Ok so here is my very first attempt at building a charcoal retort. This first one uses a 10 Gallon and a 30 gallon metal drum with sealable lids.
Ok the retort vessel that the material you are trying to convert to charcoal must be vented. So what I did here was install a center venting tube in the ten gallon drum. This allows the gas to vent from the top and then down. The Pyrolysis gases produced once the moisture is cooked out is flamable and can be used to provide process heat. This makes this much more efficient. However the water your gross feedstock the more smoke this thing is going to make. So if no smoke is desired you will want to run only seasoned feed stock that is dried bellow 20% MC.
On the 30 gallon barrel that contains the combustion process has two 1 inch tubes installed just bellow the bottom stiffening ring of the barrel. These tubes serve two purposes. One is to support the retort drum inside and to suppoly second stage air to the Pyrolysis gas that is produced. I drilled (5) 3/8 holes spread 1 1/2 inches appart centered in the span of the tubes.
The 30 gallon drum lid I addapted a duct flange to addapt 6 inch stove pipe for the chimney. I added 1 1/2 inch ball valve to feed the primary oxidation process. I am probbably going to add a second one to the opposing side. Then I simply fabbed up a simple door to feed the fire box with a pull latch to secure it.