Nice job on the drawing. That is a large project, with a tremendous amount of heat involved! What exactly is this “furnace plaster”? Is it firebrick like is used in ceramic kilns? Or are you considering a flexible ceramic fiber product that is sprayed with a coating? (When I first saw your drawing, one of my reactions was that the door was going to warp big time.) What kind and shape of wood are you planning to bake? How large are the pieces, and will there be some way for the heat to reach into all of the material? For example, you could stack them like the people at Jack Daniels Whiskey do…in a criss-cross overlapping pattern, shown here:
One time I decided to load my little propane bottle sized retort with charcoal “brands” (wood not fully converted to charcoal) and run it. I found out that packed charcoal is a good insulator. I guess you realize that your material to be converted to charcoal should be very dry. Will there be some waste heat that could be used to dry the material for the next load?
Where are you located? Looking forward to the next report.