Fueling a Charchoal Kiln from a Gasifier

Hello Guys,

I know that you asked me to send whatever sketch that I have for your review but I believe in quality and has found someone to do the drawings for me properly especially so one can appreciate the dimensions .

I will be using the actual size that I intend to start operations with.

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Hello Ava Zim,
Have you seen the portable Exeter Charcoal Retort? Here is a YouTube video posted last month (Feb. 2017). If you are in the U.S., there is a distributor. In the video, the people making charcoal say that charcoal from this Exeter is better than charcoal from the Ring Kiln that they had been using.

Where are you located? What will you use to fill the retort? What is the intended use of the charcoal you will produce?
Looking forward to your drawings. There was someone wanting to buy an Exeter Retort who had a “go fund me” or similar scheme and was hoping to come up with $5000 to have the unit delivered so he could convert scrap wood from the dump into bagged charcoal, which doesn’t sound too bad for a stainless steel unit mounted on a trailer and delivered to the site.


Ok Guys after a few weeks of self tutoring in FreeCAD, I have some screenshots of the Charcoal Kiln that I have designed and will be building. Your criticisms, enhancements will be welcomed.

I have watched countless videos on how to make charcoal. So many designs. Every one of them needed a ridiculous amount of heat, under it and all around it.
I was then ready to make my own. I stayed small and used a 15 gallon oil drum. It needed fire on all sides of it and still took 3-4 hours. Most of the wood converted to charcoal, but not always. After a few times of lighting this up, the metal really took a lot of abuse.
My point? What I see you designed looks expensive. What do you plan to make this out of to endure multiple firings? How long will it take to heat up the center of this to make sure that turns into charcoal too? maybe smaller individual compartments where the heat can get to all sides?
I’m not sure where you live, because if visible smoke is an issue, I see why you want it contained. If not not, Don M. and Gary G. have systems I like for burning outside in bigger batches.


Bill Schiller,

Smokelessness is an important feature of this design. Another, is the ability to use Waste Oil, Wood, or any fuel for that matter.

Regarding the heat. This design will be able to generate alot of heat most of which will be transferred to the Charcoal Box. That is because the inner walls of the furnace and area around the charcoal box will be lined with 2" of furnace plaster to keep in the heat.

Regarding the toll on the metal of choice. Well the furnace plaster will be protecting most of the metal (5mm sheet metal). The Charcoal Box would be changed to stainless steel over time but we will start with the same 5mm sheet metal.

What are your views?

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What is really required is heat. In my design, we believe that we will be making maximum use of the heat generated by the three combustion chambers by lining most of the heat surfaces with furnace plaster. In addition the height of the device is 4’ while the width is 6’.

I am however, reviewing your idea of creating more compartments in the Charcoal box to allow heat to navigate the load much quicker. I am NOW thinking of three 4’ x 3’ x 4’ charcoal boxes with one combustion chamber directly under each with spaces between the boxes to allow for more heat navigation and transfer.

My opinion is, if you haven’t made charcoal before, build one of the proven methods done with barrels so you get an understanding of what I’m talking about. It’s a cost effective way to apply your theories to. Or build a small version of what you have here. A lot of moisture from the wood will need to go somewhere as it is cooking.
You could spend a year on here applying theories with the members of this group and get no where. Or, you can build something smaller and learn with real experience. I’m an advocate of the latter.


Sorry, with regard to the moisture (water and wood oil) I forgot to place a pipe at the bottom of the charcoal box to leak them out to an external air tight container. Actually I had it on my paper draft drawings. Thanks for reminding me.
I appreciate your view about starting small. Actually, this is a small version of the size that we really want to build. The final version may well be three times the size of this one. We have access to alot of waste oil and waste oil can produce enormous amounts of heat.

My guess is it’ll take a quite a bit of work to build a stationary gasifier that will sustain an adequate flare for 6+ hours.

Good point Bill, this has been my concern if I am every going to be fueling it by wood. I have realized that I will have to use LPG while I get to reload and wait for the gasifiers to get back to the point of producing gas. The fact is that we may not be using wood at all to fuel it as we have access to quite a large supply of waste oil.

The other problem I see here is you need a lot of heat, a lot. You have fuel lines in the same area as all this heat with no protection before they get to the burners.

Thanks Bill, I will enclose them in furnace platter which should insulate them from the heat of the furnace. You would note that the LPG line is entering the combustion chambers from under the furnace.

The oil ducts are deliberately exposed to the heat to allow for freer flow as well as a level of gasification which should aid the cleaner burning of the waste oil. But I will cover the Producer gas intake with furnace plaster. I will do the same for the air and LPG lines under the furnace.

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Hello Ava,
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.


Hi Ray,
Pls disregard the private message. I did not see your comment yet.

Thanks for the comment. I will use that pattern to load the wood to ensure heat is going through the entire stock. I plan to use wood not exceeding 3" in diameter.

I am thinking of splitting the Charcoal box in two to allow for more navigation of heat from my furnace.
Furnace plaster is same as furnace brick.


Thanks for the comment about the door. I will have to use a thicker steel for it. Good observation. Would thicker steel prevent the warping?

I would add some bolts through the interior of the oven, and then put big wing nuts on the outside to hold the metal of the door tightly closed. (Tack weld the heads of the bolts on the inside.) Here is a screenshot of the Exeter video above: You can see the tabs holding the gasketed door all around. Use the metal you have on hand for the first prototype. I have hauled plenty of burned out barrel carcasses to the scrapyard. When steel is glowing red hot, it is going to scale (i.e. big scabs of rust will form and fall off.) and eventually get so thin it will have to be replaced. However, your fire brick or furnace plaster will really help. If there is an air leak, extremely high temperatures will result, and bad things could happen. (Beside burning up the precious charcoal.)

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Please tell me, how long does the Exeter Retort take to cook up a batch? I can’t seem to find that information anywhere. Do you know?

Thanks Ray,

Your suggestion for securing the charcoal box is good. That should prevent the sagging given the width of the door. I also thinking of changing the orientation of the hinges from left side to bottom side. What do you think?