Couple of updates: the hood was sitting right on top of the fire, so I added a short section of heavy pipe (actually a piece of scuba tank) to lift it up a bit. Interesting to note that the fire burned a hole in its front, but not the front of the tuyere: a convincing demonstration that the water-cooled tuyere is working nicely.
I also just added some pieces of 1” thick chimney tile as a sort of “deck” around the outside. This should alleviate problems with the sand getting mixed into the coal.
Also added a deadman switch with safety cover to the blower. It’s just on/off, though, so I’m still using the variac to control the speed.
(Another good find from the industrial surplus place.)