Experimenting with small scale production of biochar

I live in a residential area of a city and cannot have a burn pile. I also noticed that some people were interested in how to make small amounts of char in their fireplaces. I see that heating the material without oxygen is the key to getting biochar... Hence my experiment.

I bought 4 #10 cans, opened them half way and froze the contents (tomato sauce) in gallon ziplock bags. I then filled each can with a different experimental ingredient: filbert nut shells, bamboo, small branches, cut to length, and banana leaves (shoved in as tight as I could get them).

I closed up the lids so that gases could escape (and ignite), but no oxygen could get in.

I put the cans on my fire which was making a regular batch of biochar.

When the cans stopped smoking/burning they were done and I removed them from the heat and sealed the top with a 3"x12" board until cool.

Some observations:
Getting the bamboo and the sticks into the right length was somewhat labor intensive.
Doing the same with the Filbert shells was easy-peasy.
Stuffing banana leaves in the cans was in between the two, but fairly quick and easy.

All 4 ingredients made very good biochar.
The easiest to pulverize was the banana leaves.

I have repeated the experiment with cut to size waste lumber, split fairly small. Also worked well.

The only question unanswered was how long do the cans last??? My first can just broke a hole in the bottom after 5 uses (But red hot each time).

I use an old BBQ to make my biochar in the city. I put the cans on top of the fire.

Jon Sousa wrote:The only question unanswered was how long do the cans last??? My first can just broke a hole in the bottom after 5 uses (But red hot each time).

You might try sourcing a small cast iron pot with a lid, which should last you a good long while.

Here's a picture of my old BBQ cooking the cans and making a regular batch of biochar.
I remove pieces as they become biochar and add more pieces as needed until the cans are cooked.

Man, that bamboo look like it would be great to draw with! I wonder what the texture is like. The overall results of all your different materials look really consistent.
The pizza places around me are always putting out large bags of #10 sauce cans for recycling, so if anyone wants to try this w/o buying the cans, that's a good place to look.
I also saw someone use stainless steel hotel pans inside a wood stove for this purpose - the lids are heavy enough to limit oxygen but loose enough to allow the material to burn. I think they were using vine or orchard trimmings.

Abe Coley wrote:

Jon Sousa wrote:The only question unanswered was how long do the cans last??? My first can just broke a hole in the bottom after 5 uses (But red hot each time).

You might try sourcing a small cast iron pot with a lid, which should last you a good long while.

Another thought I had was cutting a 3-4" hole in the top of an old propane tank and use that. (Fear not, I have recycled them before. After emptying and removing the valve by unscrewing, I fill with water and then start my cutting with it still full of water.)

Great experiment. Thanks for posting!

A niggling note: I notice that the big tomato cans have a liner to prevent corrosion. Possibly some sort of BP-x material.

Personally I would give them an initial burn and scrub with sand, or spread the first char in non-food areas. Though perhaps that's over-cautious.

I like what you did here. Never thought about using #10 cans. I have a ton of unshelled pecans, perhaps that is their final disposition.

Here is my burn barrel, I can produce a lot more in it, but the challenge becomes grinding it into "more" usable sizes.

Anyway thanks for sharing.

I use a 55 gallon barrel. I've used it, tens of times per year, for years and it's still going strong. I decided not to do this small scale biochar because I have a standard suburban yard and I"m already 60, and it would be past my death date when I got enough biochar into the soil. They are just too small.

John S
PDX OR

John,

I am fortunate to have plenty of gas grills, I could probably do something like you did with the cans and one of the burners, but of course breaking the pieces up small enough for my large burn barrel is enough work. I am not quite 60 and I haven't been doing this 10 years yet, but I am convinced biochar and compost are efforts worth undertaking, hope I have another 60 years to determine if it is worth it.

John Suavecito wrote:I use a 55 gallon barrel. I've used it, tens of times per year, for years and it's still going strong. I decided not to do this small scale biochar because I have a standard suburban yard and I"m already 60, and it would be past my death date when I got enough biochar into the soil. They are just too small.John S
PDX OR

Yeah, I get that. I'm into big volume, because I have to deal with mass volumes of material. My 55 gal kiln is the last resort -- it's just so much labour to stuff everything in there.

Still, it would be interesting to gather specimens of "perfectly made char" in sealed vessels as I burn in the barrels and trenches of my high volume "pretty good char." I confess that I chafe at fiddling with tiny bits of wood and packing them tight -- any thoughts on what the wood I might choose to do that with, for best efficiency? And should it be dry or green going into the big kiln? Green  wood is way easier to snip to length using sharp hand pruners or loppers.

The stuffs I burn tend to be light weight but bulky. I find it easier to do a top-lit open pile than using a container. It only takes minutes to burn and the char is good for making potting mix.

Douglas Alpenstock wrote:
Still, it would be interesting to gather specimens of "perfectly made char" in sealed vessels as I burn in the barrels and trenches of my high volume "pretty good char." I confess that I chafe at fiddling with tiny bits of wood and packing them tight -- any thoughts on what the wood I might choose to do that with, for best efficiency? And should it be dry or green going into the big kiln? Green  wood is way easier to snip to length using sharp hand pruners or loppers.

Yes, I have noticed that too, Douglas.  I cut the wood to the right length while it's green so that it will fit into my system.  Then I put it into a pile based on when I cut it.  Then I know if it is brown and dried.  I burn it when it has been dried, several months later.  I will often put the wood I'm about to burn under an eave, especially if the forecast looks like it might rain before I burn it.  I think dried wood makes less smoke and more char.

John S
PDX OR