Questions about brick chimney “tin man” style retort

Happy New Year Permie Biochar enthusiasts!

I tried a simple flame cap burn in a 55 gallon drum on its side with a panel cut out of it. Not real happy with the results. A lot of partially burnt wood, not fully pyrolyzed. I think my very damp climate makes it difficult to get the wood dry enough for this method to achieve the heat it needs. And also some user error, as this was my first time with this method. And a few other cons I won’t go into.

Anyway, I’d prefer a kiln retort like a tin man. However, I don’t have a ready source of 55 or 30 gallon drums to replace as they break down from oxidation. I want something more permanent.

I will have a craftsman here make an inner retort drum of stainless steel, so it lasts a lot longer. And build my outer chamber with fire bricks, for better insulation.

Two questions.

The common tin man uses a 30 gallon inside a 55 gallon drum. I don’t have a 30 gallon to measure, but online sources say the standard size is about 46cm diameter by 70-75cm height. Based on a standard 55gal, that only leaves about 5cm between the inner and outer drum and about 15 cm on top of the inner drum to squeeze in the wood fuel to fire up this process.

Seems a bit scant to me to achieve temps of 550ºF+ for pyrolysis.

I can have my retort fabricated to any size, and also build the outer brick kiln to any size.

Is there an optimum size, or space between the inner and outer drums, to get a sufficient but efficient burn?

And how many holes are recommended for the bottom of inner drum? I’ve seen suggestions of five 1/2” holes in the 30gallon. Would more holes of smaller diameter, say seven to ten 3/8” allow a more balanced release of pyrolysis gases, less chance of bursts, but still prevent oxygen from entering?

Thanks for your input.

I think removing a barrel from inside of a brick chimney would be a pain in the butt.
This design would be easier to unload:

https://www.google.com/amp/s/www.instructables.com/How-to-Make-some-Charcoal/%3famp_page=true

As built, they use cement board.
I am not sure how durable that proved to be.
Your bricks  should be fine.

Something that is close to your initial idea is this :
https://youtu.be/NrTaISI9fm4?si=vf3I2S0aCyq87OjY

William Bronson wrote:I think removing a barrel from inside of a brick chimney would be a pain in the butt.
This design would be easier to unload:

https://www.google.com/amp/s/www.instructables.com/How-to-Make-some-Charcoal/%3famp_page=true

As built, they use cement board.
I am not sure how durable that proved to be.
Your bricks  should be fine.

Something that is close to your initial idea is this :
https://youtu.be/NrTaISI9fm4?si=vf3I2S0aCyq87OjY

Thanks. Not really interested in the first method. For my climate I think the fully enclosed kiln would work better.

I based my idea on the method in the video you shared. The video is 8 years old. They haven’t responded to questions, which is why I asked here. That brick chimney design has a lot more space between the brick outer oven and inner retort bucket for filling in fuel, than does a 55/30 gallon tin man. It seems excessive. I’m trying to find a happy medium. With some input from people who have used these types of retorts.

I’m not going to be using a 30 gallon steel drum, but a custom made stainless inner retort. I can have handles fastened to the upper sides, or one on top. I don’t think it will be too difficult lifting it out when it’s finished and cooled. As long as I have sufficient space between the inner retort and the brick chimney.

The first video wouldn't load for me.

I agree with William about how much extra work it would be to continually move bricks each time. I originally planned to do that, but then I switched when I saw this video and realized that it would work much better for me:

https://duckduckgo.com/?t=ffab&q=Warmheart+biochar&atb=v401-1&iax=videos&ia=videos&iai=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DYIbGkmt1VdE

I've been making biochar this style for 6? years without any wear on the barrel and other materials.  I also live in a rainy climate, so I don't even make biochar between Thanksgiving and say, St. Patrick's Day.  Days are too short, cold, and wet here.  

The retort is great if your priority is to be able to leave it and let it go out by itself. That isn't my priority.   My problem was that it didn't make enough biochar for my needs in my garden.  

I got a 55 gallon barrel free on Craig's list and put the other stuff together by myself from Restore for about $10.

John S
PDX OR

John Suavecito wrote:I agree with William about how much extra work it would be to continually move bricks each time…

The retort is great if your priority is to be able to leave it and let it go out by itself. That isn't my priority.   My problem was that it didn't make enough biochar for my needs in my garden.

Thanks John.

I’m not planning on moving the bricks. They will be a permanent structure making up the outer “drum” of the kiln. The stainless drum will be placed inside. Then a metal lid and chimney on top. Only have to remove the chimney and lid and lift the inner drum out. I expect the inner drum to be less than 8kg, empty, maybe double that when full of processed biochar.

My rainy season is most the year. So I want to be able to fill the retort and outer kiln with material and light it up, when I have a couple hour dry window. Then it doesn’t matter if it starts raining while it’s going.

This is a really interesting project! I don't have enough room at my place to have done this, but it might work great for you and others.  I hope you take pictures so others can try this design or develop their own version.  I look forward to seeing it.

John S
PDX OR

John Suavecito wrote:I hope you take pictures so others can try this design or develop their own version.  I look forward to seeing it.

I will try to take photos while building it. And depending on how it turns out, maybe a video with description and a burn, incorporating those photos.