Hey all, I liked all the interesting ideas bouncing around in this thread, and I borrowed what I could as I launched into my own retort project. I have been making charcoal with a really inefficient retort, and I think I was burning almost as much wood as I was putting into the barrel. I did not really produce very much smoke with my setup, although it hardly matters where I am. Once I get up and running I am going to take some good measurements: Pounds of wood into the retort, pounds of wood burned to get the process going, and pounds of charcoal. Anyhow, on to the build:
I really like the look of the Hookway system, but I think Bruce is onto something with the horizontal arrangement for ease of unloading. It is nice to be able to just shovel the charcoal out when it is done. I envy that section of stainless pipe you found, btw. What I was able to find locally was a section of 6"x 5" steel box section with 3/16" walls. I welded one end closed, then cut out a hole for the chimney, and the gas inlet. Here is a picture of the firebox:
I saw in the video of the Hookway retort that he had used a short section of pipe leading down into his firebox, but when the wind shifted, it would allow the smoke to billow out the end. I decided to do this as well, but put a bit of an angle on it, so that the gas would be directed as a jet in towards the chimney, and over the hot coals.
I used a chimney cap that bolts down to tapped holes in the little tabs in the firebox - 3/16" material was hard to weld, but it was great for tapping holes to bolt things on. I also made a flange for the door, since I wanted to be able to feed the fire and load from the same side. I welded on some captive bolts, and put some stove gasket on it, so that the door can be cinched tight, hopefully making a good seal
Here it is assembled, with the door clamped and bolted on.
I added the threaded floor flange, which will have a 90" fitting, and a lid to allow steam to escape at startup. The chimney pipe in the back I sealed with more stove gasket after I took this picture, and I also made a simple little steel cap that fits snuggly over the opening to the firebox to seal the system during cool down.
The next step is to devise a way to insulate it - I have 2 ideas, one is to take the paper off some extra fiberglass insulation i have laying around and attach it with chicken wire, the other is to build a dry-laid box out of cinder blocks, prop it up inside, and fill all the space around it with perlite (which I also have a large quantity of just laying around).
I am really excited to get this thing fired up, and would like to hear any ideas or comments. I am not sure if the thick walls of my firebox are going to be a problem (it was the thinnest material available in that size). I worry that it might be inefficient as a heat-exchanger, and that too much heat might go up the chimney. Any thoughts?