Biochar reactor using 55 gallon drums

Hello fellow Permies,

I didn't know where to put this post because biochar doesn't have its own topic. Yet, it is here because biogas is created during the pyrolysis process.

Here's the link to DIY 55 gallon biochar reactor using recycled 55 gallon drums:

http://www.highdesertresiliency.com/biochar/

Now you can start some awesome Terra Pretta!

Barrel kilns are good and you can make some really fine ones for about $400 in plumbing, but in my experience the downside is longevity -- that thin steel doesn't hold up long to the heat and corrosive gases. Lately Kelpie Wilson has been experimenting with the cone kiln, cheaper and better for some feedstocks, such as bamboo and wood scraps, less wood cutting required. She has posted videos to her website (along with the WhirlyGirl biochar making kitchen stove) at http://www.greenyourhead.com/. See too my book for permies: The Biochar Solution (2010 New Society).

Even though I have put this video up on other threads, this looks like a good place for another link to it:



I've been using this method for a couple months now, and it is FAR better than the other ways I was cooking biochar. My burns do take longer, about 6 hours to char everything all the way down to the bottom, but then I don't have as big a chimney on the top, just one about the same size as in Brett's link.

One thing that helps burn barrels hold up to the heat and corrosive gases it to bring them in after you are done with a burn. Left outside in the rain, the cycling of fire and water breaks them down in no time.

Thanks for mentioning that Cone Kiln - this is a new design for me, and it looks like it would suit how we tend to work.

Cone Kiln

I've messed around with various configurations of barrels and retorts and found that, almost universally, the yield of char for the time spent is too inconsiderable to make it worth while. Retorts can increase the % conversion of MATERIAL to biochar but that it is at the cost of considerable increase in time and expense of construction. I would rather have a less efficient but also less time consuming way of making it.

The really slow part with drum systems if you are using something like garden prunings is cutting pieces to size so they can fit into the drum tightly - lots of tedious and wrist straining work with secateurs.

For contrast, I've also made lots of biochar using open burn piles that get quenched with water. Rough cut brush just gets piled on top and the layer of char keeps building up. A single fire can process a much greater quanity of material, and produce much more char, in a given afternoon. This Cone kiln looks like a really nice compromise - the speed of using an open fire, but the metal body cuts down on some of the loses so should increase efficiency. The open shape mean you can burn rough cut and longer pieces easily. Overall a nice setup.

Just need to find a metal worker who can make me one!

what's the difference between a cone kiln and just having an open top barrel? or even a pit?

typically, the efficiency yield from this kind of method of char production is low, and smoke/pollution levels would be high.

Open top barrels don't work well because the steep sides restrict airflow so the gases given off cool significantly before they burn near the top of the barrel. The open pitch should give better air supply to the compustion surface so the gases will burn hotter and more completely. The charred material will build up in sucessive layers over time, so in one burn you could in theory end up with a cone totally full of char. In my experience of using drums I get at most 1/3rd of a drums worth for my time - and my time is valuable!

Second, the sloped sides make it nice and easy to toss in longer and more uneven pieces of brush wood/hedge trimmings etc... less processing of the wood makes life a lot easier and quicker.

Michael Cox wrote:The charred material will build up in sucessive layers over time, so in one burn you could in theory end up with a cone totally full of char.

yes, but you could do the same with a barrel, add layers as it burns, rather than all at once. The issue about efficiency is not about a full container of char, it's about how many lbs of charcoal you get from the lbs of wood you put in. With better combustion of the wood, you'll get more ash, less char.

I fail to see the difference between a cone and a pit.

Michael Cox wrote:Second, the sloped sides make it nice and easy to toss in longer and more uneven pieces of brush wood/hedge trimmings etc... less processing of the wood makes life a lot easier and quicker.

Yes, but that's just because of the opening. A larger barrel or a bigger pit would allow the same thing. A bigger container holds bigger pieces of wood.

Abe - I've done the building up of layers in drums. It does work, but it is very smokey as the fresh air cannot get down to the combustion zone. If you cut slits or another air supply into the sides of the drum you end up burning more of the char than you need to.

Regarding the cone vrs a pit in the ground - you may well be right that a pit could do this job. I've not tried it.

As far as efficiency goes - I don't really consider the supply of raw materials my limiting factor but time. I have nearly unlimited supplies of brush and hedge trimmings but cannot afford to spend huge amounts of time processing it. Hence a system that is more time efficient suits me better than one that makes the absolute most char from a given load of material. I have had burn days before using drums where I needed to do four successive batches, taking about 2 hours each to load, burn and process.

With an open fire or with the cone system I could process the whole lot in one go over about 3 hours. 5 hours of my time is worth a lot more than the "lost" biochar.

I have no problems with the design above with incomplete biogas combustion (ie, no smoke). I even used to to burn half dried Christmas tree trimmings, lots of pine resin and pitch. You can look into the barrel through the vents and see the distinct layers. The pyrolysis layer will be smoldering, you can then see the biogas and smoke rising above that, once it reaches the air intakes and chimney it erupts into a flame vortex.

I wanted to take a picture of it but some times you can see a little boundary layer (about 1/2 inch) between the bottom barrel and top intake where the biogas is and hasn't gotten enough oxygen to ignite. Above that 1/2 inch the flames glow orange and continue up the chimney.

The entire system is usually hot enough that I need to stand about 2 to 3 feet from it to be comfortable.